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Infrared waves are just beyond visible red light in the electromagnetic spectrum. What is Infrared Radiation? (5 marks)

Radiation that all objects emit. The hotter an object is, the more IR it radiates in a given time. Dark, Matt surfaces are good absorbers + good emitters of IR. Light, shiny surfaces are poor absorbers, poor emitters + good reflectors of IR. Vacuum.

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Describe the arrangement of particles in solids and liquids. (6 marks)

In a solid, the particles vibrate about fixed positions so that the solid has a fixed shape. In a liquid, particles are in contact with each other but can move about at random, so a liquid doesn’t have a fixed shape or flow.

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Describe the arrangement of the particles in a gas.

The particles are usually far apart and move at random much faster, so a gas doesn’t have a fixed shape and can flow. The density of a gas is much less than that of a solid or liquid.

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How does conduction occur?

If one end of a solid is heated, the particles at that end gain kinetic energy and vibrate more. The energy is passed to neighbouring particles + in this way the energy’s transferred through the solid.

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How does conduction occur in metals?

When metals are heated their free electrons gain kinetic energy and move through the metal transferring the energy by colliding with other particles. Therefore, all metals = good conducto

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What are poor conductors?

Most liquids and gases. Poor conductors are called insulators. Materials such as wool and fibreglass are good insulators as they contain trapped air.

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Convection occurs in fluid (liquids + gases). Explain convection currents.

When a fluid is heated it expands. The fluid becomes less dense and rises. The warm fluid is replaces by cooler, denser fluid. The resulting convection current transfers energy throughout the fluid.

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What is evaporation?

Liquid-->Gas. It takes place as the most energetic liquid molecules escape from the liquids SURFACE and enter the air. Therefore the average kinetic energy of the remaining molecules in less, so the temperature of the liquid decreases = cooling.

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What factors affect the rate at which an object transfers energy by heating depend on?

Surface are + volume, material of the object + the nature of the surface with which the object is in contact with (temp or S.A.). The bigger the temp difference between an object and its surroundings, the faster the rate at which energy is transferre

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What is the rate of evaporation increased by?

Increasing the surface area of the liquid. Increasing the temp of the liquid. Creating a draught of air across the liquid’s surface.

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What is condensation and what is it affected by?

Gas-->liquid. The rate of condensation is increased by increasing the SA + reducing the surface temperature.

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How can we maximise the rate of energy transfer to keep things cool?

By using things that are: good conductors, painted dull black + by having the air flow around them maximised.

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How can we minimise the rate of energy transfer to keep things warm?

By minimising the transfer of energy by conduction, convection and radiation. Use things that are good insulators, are white and shiny & prevent convection currents by trapping air in small pockets.

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How can you minimise the rate of energy transfer in a vacuum flask?

Plastic cap. Double walled glass (or plastic) container. Plastic protective cover. Hot or cold liquid. Surfaces inside silvered to prevent radiation. Vacuum prevents conduction and convection.

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When we heat a substance, we transfer energy to it which will increase its temperature. What is specific heat capacity?

The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1 kilogram of the substance. The greater the mass of the substance being heated, the more energy required for each degree temp change.

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What is the equation for the specific heat capacity?

E = M × c × Ө. Energy transferred (J) = Mass (kg) × specific heat capacity (J/kgoC) × temp change (oC).

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Most people want to minimise the rate of energy transfer out of their homes to reduce fuel bills. What can be fitted for this purpose?

Fibreglass loft insulation (reduce energy transfer by conduction), cavity wall insulation (traps air in small pockets) -convection, double glazing reduces- conduction through windows, draught proofing-convection, Al foil to reflect IR back into room

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What does the U-value of a material tell us?

How much energy per second passes through it. Knowing the U-values of diff materials allows us to compare them. The lower the U-value, the better the material is as an insulator.

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What are the advantages and disadvantages of solar heating panels?

Contain water that is heated by radiation from the sun that may be used to heat buildings or provide domestic hot water. Cheap to run as they don’t use fuel but are expensive to buy + install & the water isn’t heated at night.

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List 8 forms of energy.

Light, sound, kinetic, nuclear, electrical. Gravitational Potential, Elastic potential and chemical and forms of stored energy.

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What does the conservation of energy state?

Energy cannot be created or destroyed, it can only be transferred from one form to another or one place to another. This means that the total amount of energy is always the same.

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Give examples of energy being transferred to one form to another.

Swinging pendulum: GPE -->kinetic and back again as it swings. Solar cell: light – electrical. Elastic band: chemical -->EPE.

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What is a machine and what energy do we get out of a machine?

Something that transfers energy from one place to another or one form to another. Useful energy (transferred to place and form we want it) and wasted energy (not usefully transferred).

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What will eventually happen to the useful energy and the wasted energy?

Both will eventually be transferred to the surroundings and make them warm up. As the energy spreads out, it becomes more difficult to use for further energy transfers.

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What are the pros and cons of friction in machines?

Energy’s often wasted due to friction between moving parts of a machine. The energy warms the machine + surroundings, but friction can be useful i.e. in the brakes of a bicycle or car.

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Conservation of energy supports that tin a machine, the input energy = useful energy transferred + wasted energy. How can we know how efficient a machine is?

The less energy that is wasted in a machine, the more efficient the machine. Efficiency = useful energy transferred ÷ total energy supplied. No appliance can be 100% efficient (except from an electric heater).

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Why are electrical appliances extremely useful? Give examples.

They transfer electrical energy into whatever form of energy we need at the flick of a switch. Many transfer energy by heating: may be useful i.e. in kettles, but energy is often wasted. Should be designed to waste as little energy as possible.

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What is the power of an appliance?

The rate at which it transfers energy in Watts (W) or KW. An appliance with power of 1 watt transfers 1 joule of electrical energy to other forms of energy per second. P = Energy (J) ÷ time (s). Efficiency = useful power out ÷ total power in × 100%.

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Why is energy measured in kWh by mains electricity companies?

Due to the large numbers involved, the joule is not a suitable unit. A kWh is the amount of energy transferred by a 1-kilowatt appliance when used, in an hour. E (energy transferred-kWh) = P (power of appliance in kW) × t (time taken-hours)

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The electricity meter in a house records the no. of kWh of energy used. How can the cost of electrical energy supplied be calculated?

Total cost = number of kWh × cost per kWh. The cost per kWh is given on the electricity bill.

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What do we have to consider to compare the cost effectiveness of different appliances? (6)

The cost of buying/installing the appliance, the running/maintenance/environmental costs. The interest charged on a loan to buy the appliance.

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How can householders reduce their energy bills?

By buying newer, more efficient appliances and installing materials designed to reduce energy wastage i.e. loft insulation. The payback time is the time it takes for an appliance/installation to pay for itself in terms of energy savings.

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How is electricity produced in most power stations?

In most, water is heated to produce steam which drives a turbine which is couples to an electrical generator that produces electricity. The energy can come from burning a fossil fuel i.e. coal, oil or gas (obtained from long dead biological material)

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Fossil fuels are obtained from long-dead biological material. How can electricity be produced from burning a fossil fuel i.e. coal, oil or gas?

When burned they produce energy which is used to heat water to produce steam that drives a turbine, which is coupled to an electrical generator that produces the electricity.

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How can electricity be produced in a gas fired power station?

Hot gases may drive the turbine directly. A gas powered turbine may be switched on very quickly.

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How energy produced in nuclear power stations?

The nucleus of a uranium (or plutonium) atom can undergo a process called nuclear fission. These are lots of uranium nuclei, so lots of fission reactions take place, releasing lots of energy which is used to heat water, turning it into steam.

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What is a biofuel?

A fuel obtained from living or recently living organisms. Some can be used in small-scale gas fired power stations. Renewable sources of energy.

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What are the advantages of using uranium rather than fossil fuels?

Much more energy released per kg of uranium undergoing fission reaction than per kg of fossil fuels that we burn. Nuclear power stations also don’t release greenhouse gases - but produce radioactive waste that must be safely stored for a long period

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How can we use energy from wind to drive turbines directly?

In a wind turbine, the wind passing over the blades makes them rotate and drive a generator at the top of a narrow tower.

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How can energy be obtained from falling water?

At a hydroelectric power station, water is collected in a reservoir + allowed to flow downhill and turn turbines at the bottom of the hill.

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What are the advantages and disadvantages of hydroelectric power?

Renewable, free energy resource, reliable in wet areas + no production of polluting gases, but only works in wet + hilly areas & damming causes flooding and affects the local ecology.

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Describe what happens in a pumped storage system (hydroelectric power)?

Surplus energy is used at times of low demand to pump water back up the hill to the top reservoir so that at times of high demand, the water can be released to fall through the turbines + transfer the stored energy to electrical energy.

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How can use the movement of the waves on the sea to generate electricity (wave power)?

The movement of the waves drives a floating turbine that turns a generator. Then the electricity is delivered to the grid system on shore by cable.

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The level of the sea around the coast line rises and falls twice each day. These changes in sea level are called tides. How can we generate electricity using tidal power?

If a barrage is built across a river estuary, the water at each high tide can be trapped behind it. When the water is released to fall down to the lower sea level, it drives turbines.

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What is the purpose of solar cells?

To transfer solar energy (which travels through space to the Earth as electromagnetic radiation from the sun to the earth) into electrical energy. Useful to power small devices such as watches and calculators as they produce little energy.

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What can be formed by joining together large numbers of cells?

A solar panel. Water flowing though a solar heating panel is heated directly by energy from the sun. A solar power tower uses thousands of mirrors to reflect sunlight onto a water tank to heat the water and produce steam.

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What are the advantages and disadvantages of solar energy?

Pros: renewable, no production of polluting gases, reliable in hot countries in the day + free energy resource. Solar cells are unreliable in less sunny countries + produce a small amount of electricity.

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How is geothermal energy produced?

Inside the Earth by radioactive processes which heats the surrounding rock. In volcanic areas, very deep holes are drilled + cold water is pumped down to the hot rocks. There it’s heated + comes back to the surface as steam to drive turbines that tur

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What are the advantages and disadvantages of geothermal energy?

In a few parts of the world (Iceland), hot water comes up to the surface naturally + can be used to heat buildings nearby, renewable, free energy resource, no pollution. Drilling through rock = expensive. Only economically viable in few places.

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What are the disadvantages of using coal, oil, gas and uranium?

Non-renewable, the rate at which they’re being used is much faster than the rate at which they’re produced. Oil + gas will probably run out in the next 50 years, but coal will last much longer.

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Renewable energy resources won’t run out, they can be produced as fast as they’re used. However, scientists are investigating ways to reduce the environmental impact of using fossil fuels. Give an example.

Sulfur may be removed from fuel before burning. Instead of allowing CO2 to be released into the atmosphere from power stations, it could be captured and stored in old oil + gas fields.

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What is the National Grid?

How electricity is distributed in Britain. Network of pylons + cables that connects power stations to homes, schools, factories etc. As the whole country’s connected to the system, power stations can be switched in/out of the grid according to demand

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The National Grid’s voltage is 132, 000 or more + power stations produce electricity at a voltage of 25, 000 V. Why are step-up transformers used?

The voltage is increased by step-up transformers before the electricity is transmitted across the National Grid. This is because transmission at high voltage reduces the energy wasted in the cables, making the system more efficient.

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The National Grid’s voltage is 132, 000 or more + power stations produce electricity at a voltage of 25, 000 V. Why are step-down transformers used?

It would be dangerous to supply electricity to consumers at these very high voltages (after it’s increased by step up transformers). So at local substations, step-down transformers are used to reduce the voltage to 230V for use in homes + offices.

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What is the base load demand?

A constant amount of electricity that is provided by nuclear, coal-fired and oil-fired power stations. This is called the base load demand. The demand for electricity varies during the day and between summer & winter.

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How is the variable demand for electricity met by main electricity suppliers?

Using gas-fired power stations, pumped-storage schemes + renewable energy sources. Also, different types of power stations have different start up times i.e. gas-fired power station = shortest & nuclear = longest.

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What do we use waves for?

To transfer energy and information. Direction of travel = direction in which the wave transfers energy.

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What is the difference between a longitudinal wave + a transverse wave?

For a transverse wave the oscillation (perpendicular) of the particles is perpendicular to the direction in which the wave travels. For a longitudinal wave the oscillation of the particles is parallel to the direction of travel of the wave.

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Describe electromagnetic waves i.e. light waves and radio waves.

They can travel through a vacuum. There are no particles moving in an electromagnetic wave as these waves are oscillations in electric and magnetic fields. Electromagnetic waves are transverse wavers (oscillations = perpendicular to direction of trav

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Describe mechanical waves i.e. waves on springs + sound waves?

Travel through a medium (substance). Mechanical waves may be transverse or longitudinal. Sound waves are longitudinal waves (made up of compressions and rarefactions).

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How do you calculate the speed of a wave?

Wave speed in m/s = frequency (Hz) × wavelength (m)

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How does the wavelength of a longitudinal wave differ to that of transverse wave?

Transverse: distance from 1 crest/trough to the next. Longitudinal: distance from the middle of one compression/rarefaction to the next.

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How does the frequency of a longitudinal wave differ to that of transverse wave?

Longitudinal: The number of compressions passing a point in 1 second. Transverse: number of wave crests passing a point in one second.

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What is the amplitude of a wave?

The height of the wave crest or depth of the wave trough from the position at rest. The greater the amplitude of a wave, the more energy it carries.

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What is the amplitude of a wave?

The height of the wave crest or depth of the wave trough from the position at rest. The greater the amplitude of a wave, the more energy it carries.

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How do you calculate the speed of a wave (in metres per second, m/s)?

V = f (frequency in Hz) × ƛ (wavelength in metres)

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What happens to the direction and speed of waves when they cross a boundary between two substances?

The waves change speed + the wavelength of the wave changes but the frequency stays the same. The change in speed causes a change in direction but if the wave is travelling across a normal, then it won’t change direction.

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What causes dispersion?

Different colours of light have different wavelengths + are refracted by slightly different amounts. When a ray of white light is shone onto a triangular glass prism we can see this as a spectrum is produced. Violet light refracted most, red light =

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What is diffraction?

Property of all waves. It’s the spreading of waves when they pass through a gap or round an obstacle. The effect is most noticeable when: the wavelength of the waves is about the same size as the gap/obstacle.

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Why may a person not be able to receive a TV signal in a hilly area?

As the TV signals (carried by radio waves) may be blocked by a hill. The radio waves passing the hill will be diffracted round the hill. If they don’t diffract enough, the radio and TV signals will be poor.

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What allows an image to be seen in the mirror?

The reflection of light. The incident ray is the ray that goes towards the mirror, the reflected ray coming away, the normal is perpendicular to the mirror (plane).

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What is the angle of incidence and angle of reflection?

Angle of incidence: angle between the incident ray and the normal. Angle of reflection: angle between the reflected ray and the normal. For any reflected ray the angle of incidence is equal to the angle of reflection.

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What are the four features of the image (reflected) in a plane mirror?

The image is: the same size of the object, upright, the same distance behind the mirror as the object is in front and is virtual.

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What is a real image and a virtual image?

Real image: One that can be formed on a screen as the rays of light that produce the image actually pass through it. Virtual image: cannot be formed on a screen as the rays of light that produce the image only appear to pass through it.

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What are sound waves?

Longitudinal waves caused by mechanical vibrations in a medium/substance, which are detected as sound. The direction of the vibration is the same direction the wave travels.

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What can sound waves travel through?

Liquids, solids + gases – generally travel fastest in solids + slowest in gases. They can’t travel through a vacuum –tested by listening to a ringing bell in a “bell jar”, as the air’s pumped out of, the ringing sound fades away.

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What is the range of frequencies heard by the human ear?

Is from 20Hz to 20,000 Hz. The ability to hear the higher frequencies declines with age.

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How can sound waves be reflected to produce echoes?

Only hard, flat surfaces such as flat walls and floors reflect sound, soft things like carpets, curtains and furniture absorb sound and an empty room will sound different once carpets, curtains + furniture are put into it.

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How can sound be diffracted and refracted?

Sound waves can be refracted – takes place at the boundaries between layers of air at different temperatures. Sound waves can be diffracted.

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What does the volume and pitch of a note depend on?

The frequency of the sound waves. The higher the frequency, the higher the pitch. The volume depends on the amplitude of the sound waves. The greater the amp, the more energy it carries + the louder the sound.

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Why do different instruments sound different when they play the same note?

As they produce different waveforms. Tuning forks + signal generators produce ‘pure’ waveforms. Vibrations created in an instrument when it’s played produce sound waves.

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