# Physics short questions and answers

## Physics short questions and answers

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# Physics short questions and answers

Reflection

• State the laws of reflection of light. [2005 OL]
• The incident ray, the normal at the point of incidence and the reflected ray all lie on the same plane.
• The angle of incidence is equal to the angle of reflection (i = r).

• Describe the image that is formed in a concave mirror when an object is placed inside the focus.

[2003 OL] [2007 OL]
The image is virtual, magnified and upright.

• A concave mirror can produce a real or a virtual image, depending on the position of the object.

Give one difference between a real image and a virtual image. [2004 OL]
A real image can be obtained on a screen; a virtual image cannot.
In a real image the light rays meet; in a virtual image they do not.
A real image is always inverted/ a virtual is erect, a real image is in front / a virtual image is behind.

• Give two uses for a concave mirror. [2004 OL]

Torch, headlights, searchlight, dentist mirror, cosmetic mirror, solar furnace.

Refraction

• What is meant by refraction of light? [2008] [2006][2009 OL][2005 OL][2002 OL]

Refraction is the bending of light as it goes from one medium to another.

• State the laws of refraction of light. [2002][2003 OL]
• The incident ray, the refracted ray and the normal all lie in the same plane.
• Sin i/ Sin r is a constant

• State Snell’s law of refraction. [2008]

The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.

• Define the term total internal reflection. [2003 OL]

Total internal reflection occurs when the angle of incidence in the denser of the two media is greater than the critical angle and light is reflected back into the denser medium.

• Define the term critical angle. [2004 OL][2003 OL]

The critical angle corresponds to the angle of incidence in the denser of two media which causes the angle of refraction to be 900.

• Why is each fibre in an optical fibre cable coated with glass of lower refractive index? [2009]

Because total internal reflection can only occur for rays travelling from a denser to a rarer medium.

• What is meant by the refractive index of a material? [2004 OL]

n = sin i/ sin r,  where i is the angle of incidence and r is the angle of refraction.

• Give two uses of total internal reflection. [2003 OL][2005 OL]

Fibre optics, endoscopes, reflective road signs, telecommunications, binoculars, periscope.

• How is the escape of light from the sides of an optical fibre prevented? [2004 OL]

Total internal reflection occurs due to an outer cladding of lower refractive index.

• An optical fibre has an outer less dense layer of glass. What is the role of this layer of glass? [2004][2009]

Total internal reflection will only occur if the outer medium is of greater density.
It also prevents damage to the surface of the core.

• Give one use for optical fibres. [2004 OL]

Endoscope, telecommunications, binoculars.

• Give two reasons why the telecommunications industry uses optical fibres instead of copper conductors to transmit signals. [2004]

Less interference, boosted less often, cheaper raw material, occupy less space, more information carried in the same space, flexible for inaccessible places, do not corrode, etc.

• Name a material that is used in the manufacture of optical fibres. [2004 OL]

Glass / plastic / sand / silicon
Lenses

• A diverging lens cannot be used as a magnifying glass. Explain why. [2006]

The image is always diminished

• How does the eye bring objects at different distances into focus? [2002]

It can change the shape of the lens which in turn changes the focal length of the lens.

Velocity and acceleration

• Define velocity [2009 OL][2008 OL][2004 OL][2002 OL]

Velocity is the rate of change of displacement with respect to time.

• Define acceleration [2008 OL][2004 OL][2002 OL]

Acceleration is the change in velocity with respect to time

• Explain the term acceleration due to gravity, g. [2006 OL][2003 OL]

It is the acceleration of an object which is in freefall due to the attraction of the earth.

Vectors

• Give the difference between vector quantities and scalar quantities and give one example of each. [2003]

A vector is a quantity which has magnitude and direction. Example: force
A scalar is a quantity which has magnitude only. Example: mass

• Force is a vector quantity. Explain what this means. [2006 OL]

A vector is a quantity which has magnitude and direction.

Force, Mass and Momentum

• Define the Newton, the unit of force. [2008]

The Newton is the force that gives a mass of 1 kg an acceleration of 1 m s-2.

• Define Force [2004] [2008 OL][2006 OL]

A force is something which causes an acceleration.

• Define Momentum [2004][2004 OL]

Momentum = mass × velocity

• State Newton’s Second Law of Motion [2009][2004] [2003][2007 OL]

Force is proportional to the rate of change of momentum.

• State Newton’s Third law of Motion. [2006]

When body A exerts a force on body B, B exerts a force equal in magnitude (and) opposite in direction to A.

• Name two forces acting on a cheetah while it is running. [2004 OL]

Air resistance, gravity, friction

• Why is the astronaut’s weight greater on earth than on the moon? [2006 OL]

Because acceleration due to gravity is greater on the earth (because the mass of the earth is greater than the mass of the moon).

• The earth is surrounded by a layer of air, called its atmosphere.

Explain why the moon does not have an atmosphere. [2006 OL]
Because gravity is less on the moon.

• A powerful rocket is required to leave the surface of the earth.

A less powerful rocket is required to leave the surface of the moon. Explain why. [2008 OL]
The force of gravity is less on moon so less force is needed to escape.

• Using Newton’s first law of motion, explain what would happen to the passengers in a plane if they were not wearing seatbelts while the aircraft was landing.  [2002 OL]

They would continue to move at the greater initial velocity and so would be ‘thrown’ forward.

• Draw a diagram to show the forces acting on the ball when it is at position A. [2006]

Weight (W) downwards; reaction (R) upwards; force to left (due to friction or curled fingers)

• Use a diagram to show the forces acting on the skydiver and explain why he reaches a constant speed. [2003]

Weight acting down.
Air resistance / friction / buoyancy acting up.
Air resistance = weight, therefore resultant force = 0
Therefore acceleration = 0

• What is friction? [2007][2009 OL][2006 OL][2002 OL]

Friction is a force that opposes the relative motion between two surfaces in contact.

• State The Principle of Conservation of Momentum.

[2002][2009 OL][2008 OL][2007 OL][2005 OL][2004 OL]
In any interaction between two objects, the total momentum before the interaction is equal to the total momentum after the collision, provided no external forces act.

• A rocket is launched by expelling gas from its engines.

Use the principle of conservation of momentum to explain why a rocket rises. [2007 OL]
The gas moves down (with a momentum) causing the rocket to move up (in the opposite direction with an equal momentum).

• A spacecraft is approaching a space station at a constant speed. The spacecraft must slow for it to lock onto the space station. In what direction should the gas be expelled? [2002]

Forward (toward the space station).

• Explain how the principle of conservation of momentum is applied to changing the direction in which a spacecraft is travelling. [2002]

As the gas is expelled with a momentum in one direction the rocket moves in the other direction with an equal momentum.

Pressure

• Define pressure. [2006][2009 OL][2007 OL][2005 OL][2002 OL]

Pressure is Force per unit Area.

• Give the unit of pressure. [2002 OL][2005 OL]

The pascal

• Name an instrument used to measure pressure. [2002 OL][2005 OL]

A barometer

• Is pressure a vector quantity or a scalar quantity? Justify your answer. [2006]

It is a scalar quantity because it does not have a direction.

• A balloon rises through the atmosphere while the temperature remains constant.

What will happen to the balloon as it continues to rise? [2007 OL]
It will expand.

• When air is removed from a metal container it collapses. Explain why. [2002 OL]

The pressure outside (due to atmospheric pressure) is greater than the pressure inside.

• The earth is covered with a layer of air called the atmosphere.

What holds this layer of air close to the earth? [2005 OL]
Gravity.

• The type of weather we get depends on the atmospheric pressure.

Describe the kind of weather we get when the atmospheric pressure is high. [2005 OL]
Good weather, dry, clear skies, little wind, settled.

• State Boyle’s law. [2009][2006][2007 OL][2003 OL]

For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume.

• State Archimedes Principle. [2007]

When an object is immersed in a fluid, the upthrust it experiences is equal to the weight of the displaced fluid.

• State the law of flotation. [2008]For a floating object, the weight of the object equals the weight of the fluid displaced.

Gravity

• State Newton’s Law of Gravitation. [2008] [2005] [2004][2008 OL][2003 OL]

Any two objects in the universe are attracted to each other with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them.

• Give two factors which affect the size of the gravitational force between two bodies. [2006 OL]

The mass of the objects and the distance between them.

• What is the relationship between the acceleration due to gravity g and the distance from the centre of the earth? [2003]

g is proportional to 1/d2

• The international space station (ISS) moves in a circular orbit around the equator at a height of 400 km.
• What type of force is required to keep the ISS in orbit?
• What is the direction of this force? [2008]
• Gravity
• Towards the centre of the orbit / inwards / towards the earth

• An astronaut in the ISS appears weightless. Explain why. [2008]

He is in a state of free-fall (the force of gravity cannot be felt).

• Why is the acceleration due to gravity on the moon less than the acceleration due to gravity on the earth?

[2003 OL]
The earth has a greater mass than the moon.

• The earth is covered with a layer of air called the atmosphere.

What holds this layer of air close to the earth? [2005 OL]
Gravity.

• The earth is surrounded by a layer of air, called its atmosphere. Explain why the moon does not have an atmosphere. [2006 OL]

Because gravity is less on the moon.

Moments

• Define the moment of a force. [2006 OL][2003 OL]

The moment of a force is equal to the force multiplied by the distance between the force and the fulcrum.

• Why is it easier to turn a nut using a longer spanner than a shorter one? [2006]

The distance from the fulcrum is greater therefore there is a greater turning effect.

• Explain why the handle on a door is on the opposite side to the hinges of the door. [2003 OL]

In order to maximise the distance between the force and the fulcrum.

• A crane is an example of a lever. Give another example of a lever. [2006 OL]

Crowbar / nailbar / nutcracker / wheelbarrow / tongs / door handle etc.

Work, Energy and Power

• Define energy [2005 OL]

Energy is defined as the ability to do work

• Define work. [2007 OL]

Work is the product of force by displacement

• What is the difference between potential energy and kinetic energy? [2007 OL]

Potential energy is energy a body has due to its position; kinetic energy is energy a body has due to its motion.

• Name one method of producing electricity. [2005 OL]

Solar, wind, wave, tidal, biomass, coal, oil, gas, hydroelectricity, geothermal, nuclear, uranium, turf.

• What type of energy is associated with wind, waves and moving water? [2005 OL]

Renewable energy.

• Which of the following is not a renewable source of energy: wind, nuclear, solar, hydroelectric? [2007 OL]

Nuclear

• Give one disadvantage of non-renewable energy sources. [2005 OL]

They will run out.

• How does the sun produce heat and light? [2005 OL]

Through nuclear reactions.

• State one energy conversion that takes place in an electrical generator. [2003 OL]

Kinetic to electric.

• What energy conversion takes place when a fuel is burnt? [2005 OL]

Chemical to heat.

• What energy conversion takes place in a solar panel? [2004 OL]

Light to electricity, light to heat.

• Why is a fluorescent tube an efficient source of light? [2008]

Most of the (electrical) energy is converted to light (energy)

• Why is a filament light bulb not an efficient source of light? [2007]

Almost all of the energy is given off as heat.

• What is the difference between potential energy and kinetic energy? [2007 OL]

Potential energy is energy a body has due to its position; kinetic energy is energy a body has due to its motion.

• Give one factor on which the potential energy of a body depends. [2005 OL]

Mass, height, acceleration due to gravity (g).

• State the Principle of Conservation of Energy. [2008] [2005]

Energy cannot be created or destroyed; it can only be changed from one form to another.

• Define Power [2006] [2002] [2007 OL]

Power is the rate at which work is done.

• What is the unit of power? [2005 OL][2007 OL]

The watt.

Circular Motion

• Define (i) velocity [2006] and (ii) angular velocity. [2006] [2005]
• Velocity is the rate of change of displacement.
• Angular velocity is the rate of change of angle.

• Define ‘Centripetal Force’ [2005]

Centripetal Force is the force - acting in towards the centre - required to keep an object moving in a circle.

• The moon orbits the earth.

What is the relationship between the period of the moon and the radius of its orbit? [2009]The period squared is proportional to the radius cubed.

• Give an expression for centripetal force. [2004]

• Centripetal force is required to keep the earth moving around the sun. [2004]
• What provides this centripetal force?
• In what direction does this centripetal force act?
• Gravitational pull of the sun.
• Towards the centre.

Simple Harmonic Motion

• State Hooke’s Law. [2009][2007] [2003] [2002]

Hooke’s Law states that when an object is stretched the restoring force F is directly proportional to the displacement provided the elastic limit is not exceeded

• A mass at the end of a spring is an example of a system that obeys Hooke’s Law.

Give two other examples of systems that obey this law. [2002]
Stretched elastic, pendulum, oscillating magnet, springs of car, vibrating tuning fork, object bobbing in water waves, ball in saucer, etc.

• The equation F = – ks, where k is a constant, is an expression for a law that governs the motion of a body.

Name this law and give a statement of it. [2002]
Hooke’s Law states that when an object is stretched the restoring force is directly proportional to the displacement, provided the elastic limit is not exceeded.

• Give the name for this type of motion and describe the motion.

Simple harmonic motion; an object is said to be moving with Simple Harmonic Motion if its acceleration is directly proportional to its distance from a fixed point in its path, and its acceleration is directed towards that point.

Temperature and Thermometers

• What is meant by the temperature of a body? [2009 OL][2008 OL]

The Temperature of an object is a measure of the hotness or coldness of that object.

• What does a thermometer measure? [2005 OL]

Temperature

• What is the unit of temperature? [2008 OL]

The SI unit of temperature is the Kelvin (K)

• What is heat? [2008 OL]

Heat is a form of energy

• What is the difference between heat and temperature? [2003]

Heat is a form of energy.
Temperature is a measure of the hotness of an object.

• To calibrate a thermometer, a thermometric property and two fixed points are needed.

What are the two fixed points on the Celsius scale? [2005 OL]
The melting point and boiling point of water.

• Name two scales that are used to measure temperature. [2009 OL]

Celsius and Kelvin.

• Give the equation that defines temperature on the Celsius scale. [2002]

T (0C) = T(K) – 273

• What is the boiling point of water on the Celsius scale? [2009 OL]

100 °C

• The SI unit is named in honour of Lord Kelvin. What is the temperature of the boiling point of water in kelvin? [2008]

273.15 + 100 = 373.15 K

• The temperature of a body is 300 K. What is its temperature in degrees Celsius? [2003 OL]

300 – 273 = 27 0C.

• The temperature of a body is 34 °C. What is its temperature in kelvin? [2007 OL]

273 + 34 = 307 (K)

• Explain the term thermometric property. [2004] [2003][2005 OL][2004 OL][2002 OL]

A thermometric property is a property which changes measurably with temperature.

• Name the thermometric property used in a mercury thermometer. [2005 OL][2009 OL]

Length (or volume) of the liquid.

• What is the thermometric property of a thermocouple? [2005]

emf

• Name a thermometric property other than emf. [2003][2005 OL][2006 OL][2008 OL]

Length, pressure, volume, resistance, colour

• Name one other type of thermometer and state its thermometric property. [2009 OL]

Thermistor – resistance, Thermocouple – emf, Liquid crystal - colour

• Why is it necessary to have a standard thermometer? [2003][2009][2009 OL]

Different thermometers have different thermometric properties at the same temperature.

Heat and Heat Transfer

• Define specific heat capacity. [2006] [2004][2008 OL][2002 OL]

Specific heat capacity is the heat energy required to raise the temperature of 1 kg of a substance by 1 K

• Define specific latent heat. [2004]

Specific latent heat is the heat energy required to change the state of 1 kg of a substance without a change in temperature.

• What is heat? [2003][2008 OL]

Heat is a form of energy

• [2003 OL][2004 OL][2005 OL][2006 OL][2007 OL][2008 OL][2009]

Name two methods by which heat can be transferred.

• What is meant by conduction? [2004 OL]

Conduction is the movement of heat energy through a substance by the passing on of molecular vibration from molecule to molecule, without any overall movement of the substance.

• What is convection? [2006 OL]

Convection is the transfer of heat through a fluid by means of circulating currents of fluid caused by the heat.

• Why are the pipes in the solar panel usually made from copper? [2004 OL[

It is a good heat conductor.

• What is the effect of increasing the U-value of a structure? [2002 OL]

It means that the heat conductivity of the structure is increased.

• The U-value of a house is a measure of the rate of heat loss to the surroundings.

Give two ways in which the U-value of a house can be reduced. [2004 OL]
Fibreglass in attic, insulation in cavity wall, double glazing, carpets

• In an electric storage heater, bricks with a high specific heat capacity are heated overnight by passing an electric current through a heating coil in the bricks. The bricks are surrounded by insulation.

Why is insulation used to surround the bricks? [2006 OL]
To prevent heat-loss.

• Name a material that could be used as insulation in a storage heater. [2006 OL]

Fibre glass / rockwool / cotton wool.

• What is convection? [2006 OL]

Convection is the transfer of heat through a fluid by means of circulating currents of fluid caused by the heat.

• Why is the heating element of an electric kettle near the bottom? [2002 OL]

Because hot water rises.

• Explain how the storage heater heats the air in a room. [2006 OL]

The heater heats the air which is beside it. This hot air then rises and is replaced by cold air. This process then gets repeated.

• Why does warm water rise to the top of the solar panel? [2004 OL]

The water expands when heated and therefore has a lower density and gets replaced by water which has a higher density (cold water). This is convection.

What is the difference between convection and radiation as a means of heat transfer? [2008]
Convection requires a medium, radiation does not.

• Why are the pipes in the solar panel usually painted black? [2004]

Black is a good absorber of radiation.

• Storage heaters have a large heat capacity. Explain why. [2004]

They are heated only at night  but must release energy slowly during the day.

• Why does the temperature of an athlete reduce when she perspires? [2007]

As the water evaporates it takes heat energy from the body.

Waves and Wave Motion

• Explain what is meant by the frequency of a wave? [2007 OL]

The frequency of a wave is the number of waves passing a fixed point per second.

• What is meant by the amplitude of a wave? [2005 OL]

Amplitude corresponds to the height of the wave.

• Explain the difference between Transverse and Longitudinal waves. [2005][2006 OL]

A Transverse wave is a wave where the direction of vibration is perpendicular to the direction in which the wave travels.
A Longitudinal Wave is a wave where the direction of vibration is parallel to the direction in which the wave travels.

• Explain the term diffraction[2009][2005 OL][2004 OL][2002 OL]

Diffraction is the spreading out of a wave when it passes through a gap or passes by an obstacle.

• Explain the term interference. [2005 OL][2004 OL]

Interference occurs when waves from two sources meet to produce a wave of different amplitude.

• Explain the term constructive interference. [2003]

Constructive interference occurs when two waves combine to produce a wave of greater amplitude.

• Explain the term coherent sources. [2003]

Coherent sources are waves which have the same frequency and are at in phase.

• What is the Doppler effect? [2008] [2007] [2006] [2003] [2002]

The Doppler Effect is the apparent change in frequency due to relative motion between source and observer.

Sound

• Define Sound Intensity [2007] [2002]

Sound Intensity is defined as power per unit area.

• Explain the term resonance. [2007 OL]

Resonance is the transfer of energy between two objects which have the same natural frequency.

• Explain the term natural frequency. [2007 OL]

Natural frequency is the frequency at which an object will vibrate if free to do so.

• The sound intensity level at a concert increases from 85 dB to 94 dB when the concert begins. By what factor has the sound intensity increased? [2009]

If sound intensity doubles Þ intensity level increases by 3 dB, so if intensity has increased by 9 dB then the sound intensity must have increased by a factor of 8.

The wave nature of Light

• Explain the term dispersion. [2009][2007 OL]

Dispersion is the splitting up of white light into its constituent colours.

• Explain what is meant by a spectrum. [2007 OL]

A spectrum refers to the range of colours present in white light.

• Explain the term monochromatic light. [2009 OL]

Monochromatic light is light of one wavelength only.

• Explain the term diffraction grating. [2009 OL]

A diffraction grating consists of a piece of transparent material on which a very large number of opaque (black) parallel lines are engraved.

• Explain how the diffraction grating produces a spectrum. [2009]

Different colours have different wavelengths so constructive interference occurs at different positions for each separate wavelength.

• What are complementary colours? [2003 OL]

Complementary colours are pairs of colours consisting of a primary and a secondary colour, such that when combined they give white light.

Static Electricity

• State Coulomb’s law of force between electric charges. [2005] [2003] [2007 OL]

Coulomb’s Law states that the force between two point charges is proportional to the product of the charges and inversely proportional to the square of the distance between them.

• Define electric field strength. [2009][2007] [2005] [2003] [2002]

Electric field strength is defined as force per unit charge.

• Give the unit of electric field strength. [2007][2003]

The unit of electric field strength is the newton per coulomb (N C-1).

• Give one effect of static electricity? [2008 OL]

Lightning, static discharge, receive shock after walking across carpets, attracts objects, can damage electronics.

• Identify two hazards caused by static electricity. [2004]

Electric shock / explosion in flour mills /explosion when fuelling aircraft/ damage to electronic devices / electrical storm / static cling, etc.

• The build-up of electric charge can lead to explosions. Give two examples where this could happen.

[2003 OL]
Dust e.g. flour mill explosions, inflammable vapours e.g. fuelling aircraft, lightning

• How can the build-up of electric charge on an object be reduced? [2003 OL]

By earthing the object (i.e. using a conductor to connect the object to the earth which allows the charge to flow to earth).

• Explain why the gold leaf on the electroscope diverges when a positively charged rod is brought close to the metal cap. [2005 OL]

Some of the electrons at the bottom of the electroscope are attracted to the top due to the positive charge on the rod and as a result there is an excess of positive charge on the bottom, including on the gold leaf.  Because similar charges repel the gold leaf moves away from the main section.

• Give one use of an electroscope. [2005 OL]

To detect charge

• Why is Coulomb’s law an example of an inverse square law? [2006][2005]

Force is inversely proportional to distance squared.

• Give two differences between the gravitational force and the electrostatic force between two electrons. [2005]

Gravitational force is much smaller than the electrostatic force.
Gravitational force is attractive, electrostatic force (between two electrons) is repulsive.

• All the charge resides on the surface of a Van de Graff generator’s dome. Explain why. [2007]

Like charges repel and the charges are a maximum distance apart on the outside surface of dome.

• Give an application of the fact that all charge resides on the outside of a conductor. [2007]

Electrostatic shielding / co-axial cable / TV (signal) cable / to protect persons or equipment, enclose them in hollow conductors /Faraday cages (there is no electric field inside a closed conductor), etc.

Electric Current

• What is an electric current? [2006] [2008 OL][2006 OL][2004 OL][2003 OL][2002 OL]

An electric current is a flow of charge.

• What is the unit of electric charge? [2003 OL]

The ampere.

Potential Difference and Capacitance

• Define potential difference. [2009][2005] [2004][2002 OL]

Potential difference is the work done in moving a charge of 1 Coulomb from one point to another.

• Explain the term emf. [2003]

The term emf is used to describe a potential difference when it applies to a full circuit.

• Name a source of potential difference. [2008 OL]

Battery, generator, thermocouple.

• Name an instrument used to measure potential difference. [2007 OL]

A voltmeter

• Define capacitance. [2009][2008] [2004][2002 OL]

The capacitance of a conductor is the ratio of the charge on the conductor to its potential.

• Give one use of a capacitor. [2006 OL][2006 OL][2007 OL]

Store charge / (radio) tuning / smoothing / store energy / flash guns for cameras, phone charger, blocks d.c.

• List the factors that affect the capacitance of a parallel plate capacitor. [2006]

Common area of plates, distance apart, permittivity of dielectric between plates.

• How would you demonstrate that the capacitance of a parallel plate capacitor depends on the distance between its plates? [2008]

Connect the two parallel plates to a digital multi-meter (DMM) set to read capacitance.
Note the capacitance.
Increase the distance between them – note that the capacitance decreases.

Resistance

• Define resistance.  [2007] [2005]

The resistance of a conductor is the ratio of the potential difference across the conductor to the current flowing through it.

• State Ohm’s Law [2007 OL][2006 OL][2005 OL]

Ohm’s Law states that the current flowing through a conductor is directly proportional to the potential difference across it, assuming constant temperature.

• Define resistivity. [2008] [2007] [2002]

Resistivity is defined as the resistance of a cube of material of side one metre.

• Give the unit of resistivity. [2008]

The ohm-metre

• Give two uses for the multimeter. [2008 OL]

It can function as a voltmeter, ammeter or ohmmeter.

• Explain why the resistance of the bulb is different when it is not connected to the mains. [2006]

Cold filament has lower resistance

Effects of an Electric Current

• Give one use for electricity in the home. [2006 OL]

Heating / cooking / lighting /named electrical appliance etc.

• List three effects of an electric current. [2004 OL][2008 OL]

Magnetic effect, heating effect and chemical effect.

• Describe an experiment that demonstrates the heating effect of an electric current. [2002][2004 OL]

Connect a electrical calorimeter containing water to a power supply and notice the increase in temperature using a thermometer.

• State two factors on which the heating effect of an electric current depends. [2004 OL]

Size of current, length of coil.

• Explain why high voltages are used in the transmission of electrical energy. [2005]

High voltages result in smaller currents therefore less energy is lost as heat.

• Suggest a method of reducing the energy “lost” in ESB power lines. [2002]

Transfer the electrical energy at a higher voltage which would result in a lower current, therefore less energy lost as heat.

• Name two safety devices that are used in domestic electric circuits. [2004 OL][2005 OL][2007 OL]

Fuse, miniature circuit breaker, residual current device, earthing, 3 pin plug etc.

• What is the colour of the earth wire in an electric cable? [2006 OL]

Green and yellow

• What is the colour of the wire that should be connected to the fuse in a plug? [2009 OL]

Brown

• Give the standard colour of the insulation on the wires connected to each of the terminals L, N and E on the 3 pin plug. [2003 OL]

L (live) is brown, N (neutral) is blue, E (earth) is green-yellow

• What is the purpose of the wire connected to the terminal E on the plug? [2003 OL]

The earth wire protects from electrocution / shock by conducting the current to earth.

• Name and give the colour of the wire that should be connected to the fuse in a standard three-pin plug. [2004] [2008 OL]

Live, brown

• Give one safety precaution that should be taken when wiring a plug. [2006 OL]

Screw connections are fully tightened / fit the correct size fuse / ensure to match the colour codes

• Explain why a fuse is used in a plug. [2003 OL][2009 OL]

It ‘blows’ and breaks the circuit if too large a current flows, preventing possible electrocution.

• Explain how a fuse works. [2009 OL]

When too high a current flows the thin wire heats up  and melts which breaks the circuit.

• What will happen when a current of 20 A flows through a fuse marked 13 A? [2006 OL]

The fuse blows which stops the current.

• Why would it be dangerous to use a fuse with too high a rating? [2009 OL]

It would allow too large a current to flow so the device could overheat.

• Explain why replacing a fuse with a piece of aluminium foil is dangerous. [2004]

If a very large current flows the foil may still not break and so may start a fire.

• Name a common material used to conduct electricity in electric cables. [2006 OL]

Copper

• Some electrical appliances are supplied with two-pin plugs. Why is an earth wire not required in these devices? [2004][2006 OL]

They have a plastic housing so even if they are in contact with a live wire the current will not travel along the cover.

• Why is the coating on electric cables made from plastic? [2006 OL]

It is an insulator.

• A toaster has exposed metal parts. How is the risk of electrocution minimised? [2008]

The metal parts are earthed.

• Bonding is a safety precaution used in domestic electric circuits. [2003 OL]

How does bonding improve safety in the home?
Bonding is where all metal pipes are connected to earth preventing accidental electrocution.

MCBs and RCDs

• Name another device with the same function as a fuse. [2009 OL]

Circuit breaker, trip switch, RCD, MCB

• What is the purpose of a miniature circuit breaker (MCB) in an electric circuit? [2003][2002 OL]

It behaves as a fuse when too large a current flows

• When will an RCD (residual current device) disconnect a circuit? [2009]

When the magnitude of the current flowing in is different from that flowing out.

• An RCD is rated 30 mA. Explain the significance of this current. [2006]

The RCD trips the circuit if the current reaches 30 mA.

• What is the purpose of a residual current device (RCD) in an electrical circuit? [2004][2002]

It acts as a safety device by breaking the circuit if there is a difference between the live and the neutral in a circuit.

• Name a device that is often used nowadays in domestic electric circuits instead of fuses. [2003 OL]

Miniature circuit breakers (MCBs) or residual current devices (RCDs).

• Give one advantage of a Residual Current Device (RCD) over a Miniature Circuit Breaker (MCB). [2004]

RCD responds v. Quickly, RCD responds to tiny currents

• What are the charge carriers when an electric current passes through an electrolyte? [2008]

Ions

• How would the VI graph for a metal differ if its temperature were increasing? [2003]

If temperature was increasing it would no longer be linear; instead there would be a curve to the right because resistance would increase.

• What is the kilowatt-hour? [2004 OL]

The kilo-watt hour is the amount of energy used by a 1000 Watt appliance in one hour.

• What is the function of the ESB meter? [2006 OL]

It records the amount of units used.

Semiconductors

• What is a semicnductor? [2003 OL][2006 OL][2009 OL]

A semiconductor is a material whose resistivity is between that of a conductor and insulator.

• Name a material used in the manufacture of semiconductors. [2003 OL][2006 OL]

Silicon, germanium

• Why is silicon a semiconductor? [2007]

It has a resistivity between that of a conductor and an insulator.

• Give one difference between conduction in metals and conduction in semiconductors. [2002 OL]

There are two types of charge carriers (holes and electrons) in semiconductors, whereas with metals electrons are the only charge carriers.
Conduction increases with temperature for semiconductors whereas conduction decreases with temperature for metals.

• As the temperature of a room increases, explain why the resistance of a thermistor decreases. [2005]

More energy is added to the thermistor therefore more electrons are released and are available for conduction.

• Give two uses of semiconductors. [2002 OL]

Rectifiers, transistors, diodes, thermistors, thermometers, radios/TV, etc.

• Give a use for a thermistor. [2005 OL]

Thermometer, heat sensor, temperature control.

• What is doping? [2004][2003 OL][2009 OL]

Doping is the addition of a small amount of atoms of another element to a pure semiconductor to increase its conductivity.

• Semiconductors can be made p-type or n-type. How is a semiconductor made p-type? [2002 OL]

By doping it with Boron.

• Explain how the presence of phosphorus and boron makes silicon a better conductor. [2009]

When phosphorus is added more electrons become available as charge carriers.
When boron is added more positive holes become available as charge carriers.

• Give one difference between a p-type semiconductor and an n-type semiconductor. [2003 OL]

P-type material contains more holes than n-type material.
N-type material contains more free electrons than p-type material.

• What are the charge carriers when an electric current passes through a semiconductor? [2008][2003 OL]

Electrons and (positive) holes

•  What is a p-n junction? [2003 OL][2006 OL]

A p-n junction is the region connecting the p-type semiconductor to the n-type semiconductor

• What happens at the boundary of the two adjacent layers? [2009]

Electrons and holes cross the junction cancelling each other out and recombine and as a result there are no free charge carriers.
A depletion layer is therefore formed between the n-type and p-type regions and as a result a junction voltage is created.

• A p-n junction is formed by taking a single crystal of silicon and doping separate but adjacent layers of it.  A depletion layer is formed at the junction. Explain how a depletion layer is formed at the junction. [2004][2009 OL]

Electrons from n-type and holes from p-type cross the junction and recombine cancelling each other out and as a result there are no free charge carriers across this narrow insulating region.
A depletion layer is therefore formed which now acts as a ‘barrier’ between the n-type and p-type regions and as a result a junction voltage is created.

• [2009]
• Describe what happens at the boundary when the semiconductor diode is forward biased.
• Describe what happens at the boundary when the semiconductor diode is reverse biased.

The depletion layer breaks down and the diode conducts.
The width of depletion layer gets increased and the region acts as an insulator.

• Why does the p-n junction become a good conductor as the potential difference exceeds 0.6 Volts? [2004]

The depletion layer is overcome and as a result a large current flows.

• What is a diode? [2003 OL]

A diode is a device that allows current to flow in one direction only.

• Give a use of a semiconductor diode. [2009]

A rectifier

• Give an example of a device that contains a rectifier. [2003 OL]

Radio, television, computer, battery charger, mobile phone charger.

Magnets and magnetic fields

• What is a magnetic field? [2003 OL][2005 OL][2006 OL][2009 OL]

A Magnetic Field is any region of space where magnetic forces can be felt.

• Give one use of the earth’s magnetic field. [2004][2003 OL]

Navigation, protective layer around the earth which deflects dangerous cosmic rays (sometimes called solar winds).

• Why does a magnet that is free to rotate point towards the North? [2007]

It is the north end of the magnet which is being attracted to the south-end of the Earth’s magnetic field (which is located at what we call the north pole).

• A solenoid carrying a current and containing an iron core is known as an electromagnet.

Give one use of an electromagnet. [2006 OL]
Electric bell / scrap yard crane / speaker / doorbell.

• State one advantage of an electromagnet over an ordinary magnet. [2006 OL]

It can be turned on and off.

Current in a Magnetic Field

• A current-carrying conductor experiences a force when placed in a magnetic field. Name two factors that affect the magnitude of the force. [2002][2002 OL][2005 OL]

Strength of magnetic field, size of current flowing, length of conductor in magnetic field.

• Name two devices that are based on the principle that a current-carrying conductor in a magnetic field experiences a force. [2002 OL][2002 OL][2006 OL]

Motor, galvanometer, loudspeaker.

• State the principle on which the definition of the ampere is based. [2007]

A current-carrying conductor in a magnetic field experiences a force.

• Define the ampere, the SI unit of current. [2006][2003]

The ampere is the amount of charge which, if flowing in  two very long parallel wires one metre apart in a vacuum will experience a force of 2 × 10-7 N per metre length.

• Give an expression for the force acting on a charge q moving at a velocity v at right angles to a magnetic field of flux density B. [2003]

F = Bqv

Electromagnetic Induction

• Explain the term emf[2003]

emf stands for electromotive force. It is a potential difference applied to a full circuit.

• What is electromagnetic induction? [2008][2004][2002][2002 OL][2004 OL][2007 OL][2008 OL]

Electromagnetic Induction occurs when an emf is induced in a coil due to a changing magnetic flux.

• State Faraday’s law of electromagnetic induction. [2007][2005]

Faraday’s Law states that the size of the induced emf is proportional to the rate of change of flux.

• State Lenz’s law of electromagnetic induction. [2002]

Lenz’s Law states that the direction of the induced emf is always such as to oppose the change producing it.

• State the laws of electromagnetic induction. [2008][2003]

• Define magnetic flux. [2006][2005]

Magnetic flux is defined as the product of magnetic flux density multiplied by area.

• Electricity produced in a generating station is a.c. What is meant by a.c.? [2008 OL]

Alternating current

• What is a diode?

[2003 OL] A diode is a device that allows current to flow in one direction only.

• Give an example of a device that contains a rectifier. [2003 OL]

Radio, television, computer, battery charger, mobile phone charger.

• Name a device that is based on electromagnetic induction. [2004 OL][2005 OL]

Dynamo, generator, induction motor, transformer, dynamo

• What is a transformer used for? [2003 OL]

To increase or decrease voltage.

• The transformer is a device based on the principle of electromagnetic induction. Name two devices that use transformers. [2002 OL][2007 OL]

Computer, radio, TV, doorbell, washing machine, mobile phone chargers, power supply, etc.

• How is the iron core in a transformer designed to make the transformer more efficient? [2002 OL]

It has a laminated core.

• The efficiency of a transformer is 90%. What does this mean? [2002 OL]

10% of the power in is lost.

• State one energy conversion that takes place in an electrical generator. [2003 OL]

Kinetic to electric.

The Electron

• List two properties of the electron. [2003][2003 OL][2005 OL][2006 OL][2008 OL]

Negative charge, negligible mass , orbits nucleus, no internal structure, deflected by electric / magnetic field etc.

• Name another subatomic particle. [2005 OL]

Proton, neutron.

• Name the Irishman who gave the electron its name in the nineteenth century. [2003]

George Stoney

• What is thermionic emission? [2002 OL][2009 OL]

Thermionic emission is the emission of electrons from the surface of a hot metal.

• Give two ways of deflecting a beam of electrons. [2008] [2002 OL][2005 OL]

By means of an electric field and a magnetic field.

• What are cathode rays? [2009 OL]

Cathode rays are streams of high speed electrons.

• Give a use of a cathode ray tube. [2002 OL][2005 OL][2009 OL]

Old-style televisions/ computer monitor, X-ray machine/oscilloscope /heart monitor/ECG.

• How are electrons accelerated in a cathode ray tube? [2007]

By a the high positive voltage at the anode.

• What happens when the electrons hit the screen? [2005 OL][2009 OL]

Light is emitted (the screen fluoresces).

• What happens to the energy of the electron when it hits the screen of the CRT? [2003]

It gets converted to light.

•  Which one of the following is emitted from a metal surface when suitable light shines on the metal?

protons,     neutrons,       electrons,        atoms [2004 OL]
Electrons

• Distinguish between photoelectric emission and thermionic emission. [2004]

Photoelectric Effect: Emission of electrons when light of suitable frequency falls on a metal.
Thermionic Emission: Emission of electrons from the surface of a hot metal.

• What is the photoelectric effect? [2008][2005][2003][2005 OL][2008 OL]

The Photoelectric Effect is the emission of electrons from a metal due to light of a suitable frequency falling upon it.

• Give one application of the photoelectric effect. [2005][2006 OL][2009 OL]

Sound track in film, photography, counters, photocell, burglar alarm, automatic doors, etc.

• What is a photon? [2003 OL][2009]

A photon is a packet of electromagnetic radiation.

• Why as the quantum theory of light revolutionary? [2008]

Light has a particle nature (as well as a wave nature)

• A freshly cleaned piece of zinc metal is placed on the cap of a negatively charged gold leaf electroscope and illuminated with ultraviolet radiation. [2004]
• Explain why the leaves of the electroscope collapse.

Photoelectric emission occurs (electrons get emitted from the surface of the metal).
The leaves become uncharged and therefore collapse.

• Explain why the leaves do not collapse when the zinc is covered by a piece of ordinary glass.

Ordinary glass does not transmit UV light

• Explain why the leaves do not collapse when the zinc is illuminated with green light.

The energy associated with photons of green light is too low for the photoelectric effect does not occur, so no electrons are emitted from the electroscope.

• Explain why the leaves do not collapse when the electroscope is charged positively.

Any electrons emitted are attracted back to the positive electroscope.

• In an experiment to demonstrate the photoelectric effect, a piece of zinc is placed on a gold leaf electroscope.

The zinc is given a negative charge causing the gold leaf to deflect. [2006 OL]

• Explain why the gold leaf deflects when the zinc is given a negative charge.

Some of the excess electrons flow down to the bottom and the gold leaf moves away from the main section because similar charges repel.

• Ultraviolet radiation is then shone on the charged zinc and the gold leaf falls. Explain why.

Many electrons are emitted from the zinc as a result of the ultraviolet radiation shining on it. Electrons from the main part of the electroscope flow up to replace this so there aren’t as many electrons on the gold leaf to feel the repulsion.

• What is observed when the experiment is repeated using infrared radiation?

Infrared radiation will not have sufficient energy to release electrons so the gold leaf will not diverge to begin with.

• Give two applications of a photocell. [2003 OL] [2002 ][2008 OL]

Burglar alarm, smoke alarms, safety switch, light meters, automatic lights, counters, automatic doors, control of central heating burners, sound track in films, scanner  reading bar codes, stopping conveyer belt, solar cells etc.

• What are X-rays? [2006][2004 OL][2007 OL]

• Give one use of X-rays. [2004 OL][2007 OL]

To photograph bones/ internal organs, to treat cancer, to detect flaws in materials.

• Who discovered X-rays? [2006]

X-rays were discovered by Wilhelm Röntgen in 1895 (shouldn’t have got asked – not on the syllabus).

• How are X-rays produced? [2009]

Accelerated (fast moving) electrons strike a (heavy) metal target causing electrons in the target to rise to a high orbital level. When these electrons fall back down to a lower lever they emit they energy as X-rays.

• How are the electrons emitted from the cathode? [2006][2005][2004 OL][2007 OL]

The electrons are emitted from the cathode due to thermionic emission because the filament is hot.

• How are the electrons accelerated? [2006]

By the high voltage between the anode and cathode.

• What is the function of the high voltage across the X-ray tube? [2004 OL][2007 OL]

To accelerate the electrons.

• Name a suitable material for the target T in the X-ray tube. [2004 OL][2007 OL]

Tungsten

• What happens when the electrons hit part B? [2007 OL]

Some inner electrons in the tungsten target get bumped up to a high orbital, then quickly fall back down to a lower lever, emitting X-rays in the process.

• Why is a lead-shield normally put around an X-ray tube? [2002 OL]

For protection (to prevent X-rays entering the body).

• Give one safety precaution when using X-rays. [2007 OL]

• Justify the statement “X-ray production may be considered as the inverse of the photoelectric effect.” [2002]

X-ray: Electrons in, electromagnetic radiation is emitted.
Photoelectric:  electromagnetic radiation in and electrons are emitted.

The Atom, the Nucleus and Radioactivity

• Rutherford had bombarded gold foil with alpha particles. What conclusion did he form about the structure of the atom? [2005]

The atom was mostly empty space with a dense positively-charged core and with negatively-charged electrons in orbit around it.

• What is the structure of an alpha particle? [2009][2005][2008 OL]

An alpha particle is identical to a helium nucleus (composed of 2 protons and 2 neutrons).

• How are the electrons arranged in the atom? [2008 OL]

They orbit the nucleus at discrete levels.

• Describe the Bohr model of the atom. [2006]

A dense positively-charged nucleus with the negatively-charged electrons in orbit at discrete levels around it.

• Describe how an emission line spectrum is produced. [2007]

When the gas is heated the electrons in the gas are move up to higher orbital level and as they fall back down they emit electromagnetic radiation of a specific frequency.

• When the toaster is on, the coil emits red light. [2008]

Explain, in terms of movement of electrons, why light is emitted when a metal is heated.
Electrons gain energy and jump to higher energy. Then when they fall back down they emit electromagnetic radiation in the form of light.

• What is an isotope? [2007][2003][2009 OL]

Isotopes are atoms which have the same atomic number but different mass numbers.

• Give two examples of radioisotopes. [2002 OL]

Iodine, caesium, radon, carbon 14, etc.

• How many neutrons are in a 14C nucleus? [2003]

Eight

• What is radioactive decay? [2003][2003 OL]

Radioactive decay is the breakup of unstable nuclei with the emission of one or more types of radiation.

• What is radioactivity? [2004 OL][2005 OL][2007 OL]

Radioactivity is the breakup of unstable nuclei with the emission of one or more types of radiation.

• Name the three types of radiation. [2009 OL]

Alpha (α), beta (β) and gamma (γ).

• Which radiation is negatively charged? [2009 OL]

Beta (β)

• Which radiation has the shortest range? [2009 OL]

Alpha (α)

• Which radiation is not affected by electric fields? [2009 OL]

Gamma (γ)

• Name the French physicist who discovered radioactivity in 1896. [2004 OL]

Henri Becquerel (you shouldn’t have been asked this).

• What is measured in becquerels? [2002 OL]

Rate of decay, activity of a radioactive substance.

• Apart from “carbon dating”, give two other uses of radioactive isotopes. [2003][2002 OL][2005 OL]

Medical imaging, (battery of) heart pacemakers, sterilization, tracers, irradiation of food, killing cancer cells, measuring thickness, smoke detectors, nuclear fuel, detect disease,  detect leaks.

• Give two examples of radioisotopes. [2002 OL]

Iodine, caesium, radon, carbon 14, etc.

• Name an instrument used to detect radiation/ alpha particles/ measure the activity of a sample.

[2008][2007][2003 OL][2004 OL][2005 OL][2007 OL][2008 OL][2009 OL]
Geiger Muller tube.

• What is the principle of operation of this instrument? [2008][2007][2004 OL]

Incoming radiation causes ionisation of the gas.

• Give an application of radioactivity. [2005]

Smoke detectors, carbon dating, tracing leaks, cancer treatment, sterilising, etc.

• Give one use of a radioactive source. [2004 OL]

Carbon dating, radiotherapy, sterilising medical equipment, killing bacteria in food, smoke alarm

• Distinguish between radioactivity and fission. [2005]

Radioactivity is the breakup of unstable nuclei with the emission of one or more types of radiation.
Nuclear Fission is the break-up of a large nucleus into two smaller nuclei with the release of energy (and neutrons).

• Radioactivity causes ionisation in materials. What is ionisation? [2005]

Ionisation occurs when a neutral atom loses or gains an electron.

• Explain the term half-life. [2007][2002 OL][2005 OL]

Time for half the radioactive nuclei in a sample to decay

• 14C decays to 14N. Write an equation to represent this nuclear reaction. [2003]

• Cobalt−60 is a radioactive isotope and emits beta particles.

Write an equation to represent the decay of cobalt−60. [2005]

• Write a nuclear equation to represent the decay of carbon-14 by beta emission. [2007]

146C   →  714N  + -10e          ( accept e in lieu of β)

• 14C decays to 14N. Write an equation to represent this nuclear reaction. [2003]

146C   →  714N  + -10e

• Cobalt−60 is a radioactive isotope and emits beta particles. [2005]

Write an equation to represent the decay of cobalt−60.

• Why does the 12C in dead tissue remain “undisturbed”? [2003]

It is not radioactive / it is not exchanging with the atmosphere /  it is stable.

• What is meant by background radiation? [2002 OL]

• Give two precautions that are taken when storing the plutonium / dealing with radioactive sources.

[2003 OL][2004 OL]
Use thick shielding, use a tongs, use protective clothing, etc.

• Give two effects of radiation on the human body. [2004 OL][2002 OL]

Cancer, skin burns, sickness, cataracts, cause sterility, genetic, etc.

Fission, Fusion and Nuclear Energy

• What is meant by nuclear fission? [2007][2004][2002][2002 OL][2003 OL][2004 OL][2006 OL][2009 OL]

Nuclear Fission is the break-up of a large nucleus into two smaller nuclei with the release of energy (and neutrons).

• Name a material in which fission occurs. [2006 OL]

Uranium, Plutonium.

• In 1939 Lise Meitner discovered that the uranium isotope U–238 undergoes fission when struck by a slow neutron. Barium–139 and krypton–97 nuclei are emitted along with three neutrons.

Write a nuclear reaction to represent the reaction. [2008]

• Name two parts of a nuclear fission reactor.

Fuel rods, control rods, shielding, moderator, coolant.

• Name a fuel used in a nuclear reactor. [2009 OL]

Plutonium or uranium.

• What is the function of the moderator in a fission reactor? [2007][2004]

To slow down fast neutrons to facilitate fission.

• What is the role of neutrons in nuclear fission? [2009 OL]

To make the nucleus unstable which causes fission.

• In a nuclear fission reactor, neutrons are slowed down after being emitted. [2008]

Why are the neutrons slowed down?
Only slow neutrons can cause (further) fission.

• How are fast neutrons slowed down? [2008]

They collide with the molecules in the moderator.

• In a nuclear reactor, how can the fission be controlled or stopped? [2009 OL]

Dropping the control rods absorbs the neutrons and prevents further fission

•  How do cadmium rods control the rate of fission? [2004]

They absorbed neutrons which would otherwise cause fission.

• Describe what happens to the coolant when the reactor is working. [2006 OL]

It gets hot.

• What is the purpose of the shielding? [2006 OL]

It prevents radiation from escaping and harming humans.

• Name a material used as shielding in a nuclear reactor. [2005 OL][2006 OL]

• What is a chain reaction? [2003 OL]

This occurs when at least one neutron gets released during fission causing more fission to occur in another nucleus and this then becomes a self-sustaining reaction.

• Describe how a chain reaction occurs in the fuel rods. [2006 OL]

A neutron is fired into the material and this splits the nucleus of one of the atoms releasing more energy and neutrons. This process then continues.

• Explain how the chain reaction is controlled. [2006 OL]

The control rods can move up and down and when they are lowered they absorb the neutrons which prevents further fission.

• How is the energy produced in a nuclear reactor used to generate electricity? [2009 OL]

The energy produced is converted to heat. This is used to generate steam which drives a generator.

• Give one advantage and one disadvantage of a nuclear reactor as a source of energy. [2009 OL]

Advantage; abundant fuel / cheap fuel / no greenhouse gases / no global warming , etc.
Disadvantage; risk of nuclear contamination / fallout / difficulty of dealing with waste / dangerous, etc.

• Name three types of radiation that are present in a nuclear reactor. [2003 OL]

Alpha, beta and gamma.

• Give one effect of a nuclear fission reactor on the environment. [2006 OL]

It can cause pollution due to nuclear waste.

• Give one positive and one negative environmental impact of fission reactors. [2008]

Positive: no CO2 emissions / no greenhouse gases / no gases to result in acid rain / less dependence on fossil fuels.
Negative: radioactive waste / potential for major accidents etc.

• Distinguish between radioactivity and fission. [2005]

Radioactivity is the breakup of unstable nuclei with the emission of one or more types of radiation.
Nuclear Fission is the break-up of a large nucleus into two smaller nuclei with the release of energy (and neutrons).

• Give an application of fission. [2005]

Generating electrical energy, bombs

• Give one precaution that should be taken when storing radioactive materials. [2006 OL]

Store in lead or use a tongs when handling.

In Einstein’s equation E = mc2, what does c represent? [2005 OL]

• The speed of light.
• Distinguish between fission and fusion. [2006]

Nuclear Fission is the break-up of a large nucleus into two smaller nuclei with the release of energy (and neutrons).
Nuclear Fusion is the combining of two small nuclei to form one large nucleus with the release of energy.

• What is meant by nuclear fusion? [2003] [2008 OL]

Nuclear fusion is the combining of two small nuclei to form one large nucleus with the release of energy.

• What is the source of the sun’s energy? [2007][2009 OL]

Nuclear fusion

• How does the sun produce heat and light? [2005 OL]

Through nuclear reactions.

• The core of our sun is extremely hot and acts as a fusion reactor.

Why are large temperatures required for fusion to occur? [2006]
Nuclei are positively charged so enormous energy is required to overcome the very large repulsion.

• In the sun a series of different fusion reactions take place. In one of the reactions, 2 isotopes of helium, each with a mass number of 3, combine to form another isotope of helium with the release of 2 protons. [2006]

Write an equation for this nuclear reaction.

• Give one benefit of a terrestrial fusion reactor under each of the following headings: [2006]
• fuel; (b) energy; (c) pollution.
• Fuel: plentiful / cheap
• Energy: vast energy released
• Pollution: little (radioactive) waste / few greenhouse gases

• Controlled nuclear fusion has been achieved on earth using the following reaction.

What condition is necessary for this reaction to take place on earth? [2006]
Very large energy/temperature is necessary.

Particle Physics

• In the Cockcroft and Walton experiment how were the protons accelerated? [2009]

They were accelerated by the very large potential difference which existed between the top and the bottom

• In the Cockcroft and Walton experiment how were the alpha particles detected? [2009]

They collide with a zinc sulphide screen, where they cause a flash and get detected by microscopes.

• Explain why. High voltages can be used to accelerate alpha particles and protons but not neutrons.[2005]

Alpha particles and protons are charged, neutrons are not.

• Most of the accelerated protons did not split a lithium nucleus. Explain why. [2009]

The atom is mostly empty space so the protons passed straight through.

• Write a nuclear equation to represent the splitting of a lithium nucleus by a proton.

[2009] [2007] [2005][2002]
+  ®  + K.E.

• Circular particle accelerators were later developed. [2005][2009]

Give an advantage of circular accelerators over linear accelerators.
Circular accelerators result in progressively increasing levels of speed/energy and occupy much less space than an equivalent linear accelerator.

• In beta decay, a neutron decays into a proton with the emission of an electron.

Write a nuclear equation for this decay. [2004]

• Give two reasons why it is difficult to detect a neutrino. [2008]

Neutrinos have no charge and very small mass.

• In beta decay it appeared that momentum was not conserved.

How did Fermi’s theory of radioactive decay resolve this? [2007]
Fermi (and Pauli) realised that another particle must be responsible for the missing momentum , which they called the neutrino.

• Momentum and energy do not appear to be conserved in beta decay.

Explain how the existence of the neutrino, which was first named by Enrico Fermi, resolved this. [2004]
Momentum and energy are conserved when the momentum and energy of the (associated) neutrino are taken into account.
Antimatter

• Compare the properties of an electron with that of a positron. [2007]

Both have equal mass / charges equal / charges opposite (in sign) / matter and anti-matter

• What happens when an electron meets a positron? [2007]

Pair annihilation occurs.

• Give one contribution made to Physics by Paul Dirac. [2003]

Dirac predicted antimatter.
Pair Production

• In an accelerator, two high-speed protons collide and a series of new particles are produced, in addition to the two original protons. Explain why new particles are produced. [2005]

The kinetic energy of the two protons gets converted into mass.

• What is the effect on the products of a pair production reaction if the frequency of the γ-ray photon exceeds the minimum value? [2003]

The electrons which were created would move off with greater speed.There may also be more particles produced.

• Write a reaction that represents pair annihilation. [2003]

e+   +    e- → 2γ

• Explain how the principle of conservation of charge and the principle of conservation of momentum apply in pair annihilation. [2003]

Total charge on both sides is zero
Momentum of positron + electron = momentum of photons

Fundamental Forces

• Baryons and mesons are made up of quarks and experience the four fundamental forces of nature.

List the four fundamental forces and state the range of each one. [2008]
Strong (short range), Weak (short range), Gravitational (infinite range), Electromagnetic (infinite range).

• List the fundamental forces of nature that pions experience. [2006]

Electromagnetic, strong, weak , gravitational

• Name the fundamental force of nature that holds the nucleus together. [2005]

The strong nuclear force.

• Beta decay is associated with the weak nuclear force. List two fundamental forces of nature and give one property of each force. [2004]

Strong: acts on nucleus/protons + neutrons/hadrons/baryons/mesons, short range
Gravitational: attractive force, inverse square law/infinite range, all particles
Electromagnetic: acts on charged particles, inverse square law/infinite range

• Name the four fundamental forces of nature. [2002]

Gravitational, Electromagnetic, Strong (nuclear), Weak (nuclear)

• Which force is responsible for binding the nucleus of an atom? [2002]

Strong

• Arrange the fundamental forces of nature in increasing order of strength. [2009]

Gravitational, weak, electromagnetic, strong.

• Give two properties of the strong force. [2002]

Short range, strong(est), act on nucleons, binds nucleus

Quark Composition and Particle Classification

• Name the three positively charged quarks. [2008]

Up, top, charm

• What is the difference in the quark composition of a baryon and a meson? [2008]

Baryon: three quarks
Meson: one quark and one antiquark

• What is the quark composition of the proton? [2008]

Up, up, down

• A kaon consists of a strange quark and an up anti-quark. What type of hadron is a kaon? [2007]

It is a meson.

• Pions are mesons that consist of up and down quarks and their antiquarks.

Give the quark composition of (i) a positive pion, (ii) a negative pion. [2006]
π+ = up and anti-down
π- = down and anti-up

• Name the three negatively charged leptons. [2006]

Electron (e) , muon (μ), tau (τ )

• Give the quark composition of the neutron. [2004]

Up, down, down

• A huge collection of new particles was produced using circular accelerators. The quark model was proposed to put order on the new particles. List the six flavours of quark. [2005]

Up, down, strange, charm, top and bottom.

• Give the quark composition of the proton. [2005]

Up, up, down.

• Leptons, baryons and mesons belong to the “particle zoo”.

Give (i) an example, (ii) a property, of each of these particles. [2003]
LEPTONS;    electron, positron, muon , tau, neutrino
Not subject to strong force
BARYONS;  proton, neutron
Subject to all forces, three quarks
MESONS   pi(on), kaon
Subject to all forces, mass between electron and proton, quark and antiquark

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### Physics short questions and answers

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#### Physics short questions and answers

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