Physics high markers

Explain how the readings on both meters change when the environmental conditions change

resistance of LDR changes when light intensity changes

• when light intensity increase resistance of LDR decreases

• overall resistance of circuit decreases

• potential difference across total resistance remains unchanged

• current in ammeter increases

• potential difference across fixed resistor increases

• potential difference across LDR decreases

• reading on the voltmeter decreases

• potential difference is shared between the components in series

• the lower the resistance of the LDR the smaller the share of the potential difference

• reading on the voltmeter decreases

Explain the changes in the arrangement and movement of the particles of a metal as the temperature of the air decreased.

cooling

• as the metal cools the particles slow down

• particles in a liquid move slower than particles in a gas

• particles in a solid move slower than particles in a liquid

• as the liquid/solid cools the particles get closer together

• as the liquid/solid cools the density increases gas to liquid

• particles change from being spread apart to touching each other

• particles will (collide with other particles more often and) change direction more often liquid to solid

• particles change from a random arrangement to a regular pattern

• particles change from moving freely to fixed positions

• particles change from moving freely/randomly to vibrating explanation

• (internal) energy (of the argon) decreases

• (kinetic) energy (of the particles) decreases with temperature

• (potential) energy (of the particles) changes with change of state (of the argon)

• forces between particles in a gas are negligible/zero

• attractive forces act between atoms when they are close to each other

• attractive forces between particles are stronger in a solid than in a liquid

Explain how the potential difference across the resistor and the lamp will change when a switch is closed.

the resistor

the potential difference across the resistor becomes 0V

because there is a short circuit across the resistor

the lamp

the potential difference across the lamp increases

because the current increases

differences between the properties of alpha, beta and gamma radiations

alpha radiation

• an alpha particle is the same as a helium nucleus

• alpha is the least penetrating

• alpha is stopped by paper or skin

• alpha has the shortest range in air

• alpha will travel a few cm in air

• because alpha is most ionising

• because alpha has a charge of +2

beta radiation

• a beta particle is an electron (emitted from the nucleus)

• beta penetrates less than gamma and more than alpha

• beta is stopped by a thin sheet of aluminium

• beta has a shorter range than gamma

• beta will travel up to 1m in air

• because beta is more ionising that gamma and less ionising than alpha

• because beta has a charge of -1

gamma radiation

• gamma radiation is an electromagnetic wave

• gamma is the most penetrating

• gamma is reduced/stopped by several cm of lead or thick concrete

• gamma has the largest range in air

• gamma will travel very large distances in air

• because gamma is least ionising

• because is uncharged

A teacher wants to demonstrate that the radioactive source emits alpha, beta and gamma radiation. - Write a method

• move the detector very close to the source

• record the count rate

• position the paper between the source and the detector

• record the new count rate

• alpha radiation will not penetrate through paper

• if the count rate with the paper is (significantly) less than without then the source emits alpha radiation

• remove the paper and position the aluminium between the source and the detector

• record the new count rate

• (alpha and) beta radiation will not penetrate through the aluminium

• if the count rate has (significantly) reduced compared with using paper then beta radiation is present

• if radiation penetrates through the aluminium then gamma radiation is present

• the experiment should be repeated and mean results calculated because radioactivity is a random process

Explain how a step-up transformer increases the efficiency of the National Grid.

potential difference is increased

(and) current decreases

(so) energy/power losses in the transmission cables decrease

Explain how the pressure in a compact space changes

(air) particles move faster

(air) particles have increased kinetic energy

(so air) particles collide more frequently with the wall / compact space

(so air) particles collide with more force with the wall / compact space

(so) the pressure increases

Describe how the actual results led to the plum pudding model of the atom being replaced by the nuclear model.

Plum pudding model

• the atom is a ball of positive charge

• electrons are embedded in the ball

Reasons why the plum pudding model was replaced

• the results were not correctly predicted by the plum pudding model

• the plum pudding model did not predict that some particles would be deflected

• the large angle deflections suggest that the atom contains a nucleus

• all deflections suggest that the nucleus is charged

• most alpha particles were not deflected suggesting that atoms are mostly empty space

Nuclear model

• mass is concentrated in the nucleus

• the nucleus is charged

• the atom is mostly empty space

• electrons orbit the nucleus in the nuclear model

Explain why efficient energy storage is important in reducing the amount of carbon dioxide released when generating electricity

(efficient energy storage means) less energy is wasted

(to reduce carbon dioxide emissions) less fossil fuel used / burned the amount of energy generated from renewable resources will need to increase or (most)

renewable resources do not generate electricity all the time

(so) efficient energy storage will help to meet the demand for energy / electricity

Explain and compare how two different types of radioactive decay can cause transmutation

Beta decay

 Atomic number increases by one

 When a neutron decays into a proton

Alpha decay

 Atomic number decreases by two

 When an alpha particle is emitted

Comparison

Both change number of protons (hence new element/transmutation)

Beta decay increases atomic number and alpha decay decreases (explicit)

Describe how the ‘National Grid’ works

• Electrical energy is transferred through the National Grid using cables.

• A step-up transformer increases the potential difference.

• Increasing the potential difference decreases the current.

• A smaller current means less energy is transferred by heating in the wires.

• Less energy is wasted as thermal energy to the surroundings.

• Step-down transformers decrease the potential difference before electricity reaches homes.

• This makes the National Grid an efficient way to transfer energy.

Describe the energy transfer in a house

• Thermal energy is transferred from the warmer house to the colder surroundings.

• Energy is transferred by conduction through walls and windows.

• Convection currents transfer energy through moving air.

• Infrared radiation transfers energy through windows and roofs.

• Loft insulation reduces conduction through the roof.

• Double glazing traps air and reduces conduction and convection.

• Cavity wall insulation reduces energy transfer through walls.

• Draught excluders reduce convection currents.

How does energy stores change on a rollercoaster

• At the top of the track, the rollercoaster has a large gravitational potential energy store.

• As the rollercoaster moves down, the gravitational potential energy decreases.

• The kinetic energy store increases as speed increases.

• Some energy is dissipated by friction between the wheels and track.

• Some energy is transferred by sound.

• Thermal energy is transferred to the surroundings.

• Total energy is conserved overall.

Explain the difference between contamination and irradiation.

• Irradiation is exposure to radiation from a source.

• The object does not become radioactive after irradiation stops.

• Contamination is when radioactive particles are transferred onto or into an object.

• A contaminated object becomes radioactive because it contains radioactive material.

• Alpha radiation is the most ionising.

• Alpha particles are dangerous inside the body.

• Radiation can damage cells and increase cancer risk.

Evaluate the use of radiation in medicine.

• Gamma radiation can be used to sterilise medical equipment.

• Radioactive tracers can be used to diagnose medical conditions.

• Radiotherapy can kill cancer cells.

• Radiation can also damage healthy cells.

• Exposure to radiation increases cancer risk.

• Medical uses are beneficial because they can save lives.

• Safety precautions reduce the risks to patients and workers.

Explain what happens to the particles in a substance when it is heated.

• Heating transfers energy to the particles.

• The internal energy of the substance increases.

• Particles gain kinetic energy.

• The particles vibrate or move faster.

• The temperature increases because the average kinetic energy increases.

• If enough energy is transferred, the substance changes state.

• During a change of state, energy is used to overcome forces between particles.

• The temperature stays constant during the change of state.

Explain how electrical appliances can be designed to reduce danger.

• A fuse melts if the current becomes too large.

• This breaks the circuit and prevents overheating.

• Circuit breakers can also break the circuit if the current is too high.

• The earth wire carries current safely to the ground if there is a fault.

• Double-insulated appliances do not need an earth wire.

• Plastic casing is an electrical insulator.

• These safety features reduce the risk of electric shock and fire.

Compare alpha, beta and gamma radiation.

• Alpha particles are the most ionising.

• Alpha radiation has the shortest range in air.

• Alpha particles are stopped by paper.

• Beta radiation is moderately ionising.

• Beta particles are stopped by thin aluminium.

• Gamma radiation is the least ionising.

• Gamma rays have the longest range in air.

• Thick lead or concrete reduces gamma radiation.

A car accelerates along a road. Describe the energy transfers that take place.

• The car’s fuel contains a chemical energy store.

• When the fuel is burned in the engine, chemical energy is transferred.

• This is transferred mainly into a kinetic energy store of the car.

• Some energy is also transferred to thermal energy stores of the engine.

• Some energy is dissipated to the surroundings as heat due to friction and air resistance.

• Sound energy is also produced and transferred to the surroundings.

• As the car accelerates, its kinetic energy increases.

• Total energy is conserved.