# unit 1

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• Created by: jonknees
• Created on: 25-03-15 15:32

a) All objects emit and absorb infrared radiation.

b) The hotter an object is the more infrared radiation it radiates in a given time.

c) Dark, matt surfaces are good absorbers and good emitters of infrared radiation.

d) Light, shiny surfaces are poor absorbers and poor emitters of infrared radiation.

e) Light, shiny surfaces are good reflectors of infrared radiation.

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## Kinetic theory

a) The use of kinetic theory to explain the different states of matter.

b) The particles of solids, liquids and gases have different amounts of energy.

## Energy transfer by heating

a) The transfer of energy by conduction, convection, evaporation and condensation involves particles, and how this transfer takes place.

b) The factors that affect the rate of evaporation and condensation.

c) The rate at which an object transfers energy by heating depends on:

• surface area and volume
• the material from which the object is made
• the nature of the surface with which the object is in contact.

d) The bigger the temperature difference between an object and its surroundings, the faster the rate at which energy is transferred by heating.

## Heating and insulating buildings

a) U-values measure how effective a material is as an insulator.

b) The lower the U-value, the better the material is as an insulator.

c) Solar panels may contain water that is heated by radiation from the Sun. This water may then be used to heat buildings or provide domestic hot water.

d) The specific heat capacity of a substance is the amount of energy required to change the temperature of one kilogram of the substance by one degree Celsius.

is energy transferred in joules, J,

is mass in kilograms, kg

is temperature change in degrees Celsius, °C

c is specific heat capacity in J / kg °C

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## Energy transfers and efficiency

a) Energy can be transferred usefully, stored, or dissipated, but cannot be created or destroyed.

b) When energy is transferred only part of it may be usefully transferred, the rest is 'wasted'.

c) Wasted energy is eventually transferred to the surroundings, which become warmer. The wasted energy becomes increasingly spread out and so becomes less useful.

d) To calculate the efficiency of a device using:

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## Transferring electrical energy

a) Examples of energy transfers that everyday electrical appliances are designed to bring about.

b) The amount of energy an appliance transfers depends on how long the appliance is switched on and its power.

c) To calculate the amount of energy transferred from the mains using:
E = P x t

• E is energy transferred in kilowatt-hours, kWh
• P is power in kilowatts, kW
• t is time in hours, h

This equation may also be used when:

• E is energy transferred in joules, J
• P is power in watts, W
• t is time in seconds, s

d) To calculate the cost of mains electricity given the cost per kilowatt-hour.

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## Generating electricity

a) In some power stations an energy source is used to heat water. The steam produced drives a turbine that is coupled to an electrical generator.

Energy sources include:

• the fossil fuels (coal, oil and gas) which are burned to heat water or air
• uranium and plutonium, when energy from nuclear fission is used to heat water
• biofuels that can be burned to heat water.

b) Water and wind can be used to drive turbines directly.

c) Electricity can be produced directly from the Sun's radiation.

d) In some volcanic areas hot water and steam rise to the surface. The steam can be tapped and used to drive turbines. This is known as geothermal energy.

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## generating electricity part 2

e) Small-scale production of electricity may be useful in some areas and for some uses, eg hydroelectricity in remote areas and solar cells for roadside signs.

f) Using different energy resources has different effects on the environment. These effects include:

• the release of substances into the atmosphere
• the production of waste materials
• noise and visual pollution
• the destruction of wildlife habitats.
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## The National Grid

a) Electricity is distributed from power stations to consumers along the National Grid.

b) For a given power increasing the voltage reduces the current required and this reduces the energy losses in the cables.

c) The uses of step-up and step-down transformers in the National Grid.

• a transformer that increases the voltage is called a step-up transformer
• a transformer that decreases the voltage is called a step-down transformer

## general properties of waves part 2

h) Waves undergo a change of direction when they are refracted at an interface.

i) The terms frequency, wavelength and amplitude.

j) All waves obey the wave equation: v = f x λ

v is speed in metres per second, m/s

f is frequency in hertz, Hz

λ is wavelength in metres, m

Candidates are not required to recall the value of the speed of electromagnetic waves through a vacuum.

k) Radio waves, microwaves, infrared and visible light can be used for communication.

• microwaves – mobile phones and satellite television
• infrared – remote controls
• visible light – photography.
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## Sound

a) Sound waves are longitudinal waves and cause vibrations in a medium, which are detected as sound.

b) The pitch of a sound is determined by its frequency and loudness by its amplitude.

c) Echoes are reflections of sounds.

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## Red-shift

a) If a wave source is moving relative to an observer there will be a change in the observed wavelength and frequency. This is known as the Doppler effect.

• the wave source could be light, sound or microwaves
• when the source moves away from the observer, the observed wavelength increases and the frequency decreases
• when the source moves towards the observer, the observed wavelength decreases and the frequency increases.

b) There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies are, the faster they are moving, and the bigger the observed increase in wavelength. This effect is called red-shift.

c) How the observed red-shift provides evidence that the universe is expanding and supports the 'Big Bang' theory (that the universe began from a very small initial point).

d) Cosmic microwave background radiation (CMBR) is a form of electromagnetic radiation filling the universe. It comes from radiation that was present shortly after the beginning of the universe.

e) The 'Big Bang' theory is currently the only theory that can explain the existence of CMBR.

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