# Physics Unit 1

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• Created by: EmiLy1703
• Created on: 09-10-15 19:38

## Energy transfer by heating - Infrared radiation

• Infrared radiation is energy transfer by electromagnectic waves
• All objects emit infrared radiation
• The hotter an object is the more infrared radiation it emits in a given time
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## Energy transfer by heating - Surfaces and radiatio

• Dark, matt surfaces emit more infrared radiation than light, shiny surfaces
• Dark, matt surfaces absorb more infrared radiation than light, shiny surfaces
• Light shiny surfaces reflect more infrared radiation than dark matt surfaces
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## Energy transfer by heating - States of matter

• Flow, shape, volume and density are all the properties used to describe each state of matter
• The particles in a solid are held next to each other in fixed positions
• The particles in a liquid move about at random and are in contact with each other
• The particles in a gas move about randomly and are much further apart than particles in a solid or liquid
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## Energy transfer by heating - Conduction

• Metals are the best conductors of energy
• Materials such as wool and fibreglass are the best insulators
• Conduction of energy in a metal due mainly to free electrons transferring energy inside the metal
• Non-metals are poor conductors because they do not contain free electrons
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## Energy transfer by heating - Convection

• Convections is the circulation of a fluid (liquid or gas) caused by heating it
• Convections takes place only in liquids and gases
• Heating a liuid or a gas makes it less dense so it rises and causes circulation
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## Energy transfer by heating - Evaporation and Conde

• Evaporation is when a liquid turns into a gas
• Condensation is when a gas turns into a liquid
• Cooling by evaporation of a liquid is due to the fater moving molecules escaping from the liquid
• Evaporation can be increased by increasing the surface are of the liquid, by increasing the liquid's temperature, or by creating a draught of air across the liquids's surface
• Condensation on a surface can be increased by increasing the area of the surface or reducing the temperature of the surface
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## Energy transfer by heating - Energy transfer by de

• The rate of energy transferred to or from an object depends on:

- the shape, size and type of material of the object

- the materials the object is in contact with

- the temperature difference between the object and its surroundings

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## Energy transfer by heating - Specific heat capacit

• The greater the mass of an object, the more slowly its temperature increases when it is heated
• The rate of temperature change of a substance when it is heated depends on:
• the energy supplied to it
• the mass
• its specific heat capacity
• Storage heaters use off peak electricity to store energy in special bricks
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## Energy transfer by heating - Heating and insulatin

• Energy transfer from our homes can be reduced by fitting
• loft insulation
• cavity wall insulation
• double glazing
• draught proofing
• U-values tell us how much energy per second passes through different materials
• Solar heating panels do not use fuel to heat water by they are expensive to buy and install
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## Using energy - Forms of energy

• Energy exists in different forms
• Energy can change from on form into another form
• When an object falls and gains peed, its gravitationsla potential energy decreases and its kinectic energy increases
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## Using energy - Conservation of energy

• Energy cannot be created or destroyed
• Conservation of energy applies to all energy changes
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## Using energy - Useful energy

• Useful energy i energy in the place we want it and in the form we need it
• Wasted energy is energy that is not useful energy
• Useful energy and wasted energy both end up being transferred to the surrounding, which become warmer
• As energy spreads out, it gets mroe and more difficult to use for further energy transfers
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## Using energy - Energy and efficiency

• The efficiency of a device = useful energy transferred by the device / total energy supplied to the device (x100%)
• No machine can be more than 100% efficient
• Measures to make machines more efficient include reducing friction, air resistance, electrical resistance and noise due to vibrations
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## Electrical energy - Electrical appliances

• Electrical appliances can transfer electrical energy into useful energy at the flick of a switch
• Uses of everyday electrical appliances include heating, lighting, making objects move (using an electric motor) and creating sounds and visual images
• An electrical appliance is designed for a particular purpose and should waste as little energy as possible
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## Electrical energy - Electrical power

• Power is rate of transfer of energy
• P = E/t
• Efficiency = useful power out/total power in (x100%)
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## Electrical energy - Using electrical energy

• The kilowatt - hour is the energy supplied to a 1kW appliance in 1 hour
• E = P x t
• Total cost = number of kWh used x cost per kWh
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## Electrical energy - Cost effective matters

• Cost effectiveness means getting the best value for money
• To compare the cost effectiveness of different appliances, we need to take account of costs to buy it, running costs and other costs such as environmental costs
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## Generating electricity - Fuel for electricity

• Electricity generators in power stations are driven by turbines
• Coal, oil and natural gas are burned in fossil fuel power stations
• Uranium or plutonium are used as the fuel in a nuclear power station. Much more energy is released per kg from uranium or plutonium than from fossil fuel
• Biofuels are renewable source of energy. Biofuels such as methane and ethanol can be used to generate electricity
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## Generating electricity - Energy from wind and wate

• A wind turbine is an electricity generator on top of a tall towe
• Waves generate electricity by turning a floating generator
• Hydroelectricity generators are turned by water running downhill
• A tidal power station traps each high tide and uses it to turn generators
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## Generating electricity - Power from the Sun and th

• Solar cells are flat solid cells that convert solar energy directly into electricity
• Solar heating panels use the Sun's energy to heat water directly
• Geothermal energy comes from the energy released by radioactiver substances deep inside the Earth
• Water pumped into hot rocks underground produces steam to drive turbines that generate electricity
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## Generating electricity - Energy and the environmen

• Fossil fuels produce increased levels of greenhouse gases which could cause global warming
• Nuclear fuels produce radioactive waste
• Renewable energy resources can affect plant and animal life
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## Generating electricity - The National Grid

• The National Grid is a network of cables and transformers that distributes electricity to our homes from distant power stations and renewable energy generators
• Step up transformers are used to step up power station voltages to the grid voltage. Step down transformers are used to step the grid voltage down for use in our homes
• A high grid voltage reduces energy loss and makes the system more efficient
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## Generating electricity - Big energy issues

• Gas fired power stations and pumped storage stations can meet variations in demand
• Nuclear, coal and oil power stations can meet base-load demand
• Nuclear power stations, fossil fuel power stations using carbon capture and renewable energy are all likely to contribute to future energy supplies
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## Waves - The nature of waves

• We use waves to transfer enegy and transfer information
• Transverse waves vibrate at right angles to the direction of energy trnasfer of the waves. All electromagnectic waves are transverse waves
• Longitudinal waves vibrate parallel to the direction of energy transfer f the waves. A sound wave is an example of a longitudinal wave
• Mechanical waves, which need a medium (substance) to travel through, may be transverse or longitudinal waves
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## Waves - Measuring waves

• For any wave, its amplitude is the height of the wave crest or the depth of the wave trough from the position at rest
• For any wave, its frequency is the number of wave crests passing a point in one second
• For any wave, its wavelength is the distance from one wave crest to the next wave crest. This is the same as the distance from one wave trough to the next wave trough
• wave speed = frequency x wavelength
• v = f x λ
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## Waves - Wave properties: reflection

• The normal at a point on a mirror is a line drwan perpendicular to the mirror
• For a light ray reflected by a plane mirror:
• The angle of incidence is the angle between the incident ray and the normal
• The angle of reflection is the angle between the reflected ray and the normal
• The law of reflection states that: the angle of incidence = the angle of reflection
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## Waves - Wave properties: refraction

• Refraction the the change of direction of waves when they travle across a boundary
• When a light ray refracts as it travels from air into glass, the angle of refraction is less than the angle of incidence
• WHen a light ray refracts as it travels from glass into air, the angle of refraction is more than the angle of incidence
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## Waves - Wave properties: diffraction

• Diffraction is the spreading out of waves when they pass through a gap or round the edge of an obstacle
• The narrower a gap is, the greater the diffraction is
• If radio waves do not diffract enough when they go over hills, radio and TV reception will be poor
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## Waves - Sound

• The frequency range of the normal human ear is from about 20Hz to about 20,000Hz
• Sound waves are vibrations that travel through a medium (substance). They cannot travel through a vacuum (as in space)
• Echoes are due to sound waves reflected from a smooth, hard surface
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## Waves - Musical sounds

• The pitch of a note increases if the frequency of the sound waves increases
• The loudness of a note increases if the amplitude of the sound waves increases
• Vibrations created in an instrument when it is played produce sound waves
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## Electromagnetic waves - The electromagnetic spectr

• The electromagnetic spectrum (in order of decreasing wavelength, increasing frequency and energy) is:
• microwaves
• light
• X-rays
• The wave speed equation is used to calculate the frequency or wavelength of electromagnetic waves
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## Electromagnetic waves - Light, infrared, microwave

• White light contains all the colours of the visible spectrum
• Infrared radiation is used for carrying signals from remote handsets and inside optical fibres.
• We use microwaves to carry satellite TV programmes and mobile phone calls
• Different types of electromagnetic radion are hazardous in different ways. Microwaves and radio waves can cause internal heating. Infrared radion can cause skin burns
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## Electromagnetic waves - Communications

• Radio waves of different frequencies are used for different purposed because the wavelength (and therefore frequency) of waves affects:
• how far they can go
• how much they can spread
• how much information they can carry
• Microwaves are used for satellite TV signals
• Further research is needed to evaluate whether or not mobile phones are safe to use
• Optical fibres are very thin transparent fibres that are used to transmit signals by light and infrared radiation
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## Electromagnetic waves - The expanding universe

• The red-shift of a distant galazy is the shift to longer wavelengths of the light from it because the galaxy is moving away from us
• The faster a distant galaxy is moving away from us, the greater its red-shift is
• All the distanct galaxies show a red-shift. The further away a distant galaxy is from us, the greater its red-shift is
• The distant galaxies are all moving away from us because the universe is expanding
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## Electromagnetic waves - The Big Bang

• The universe started with the Big Bang, a massive explosion from a very small point
• The universe has been expanding ever since the Big Bang
• Cosmic microwave background radiation (CMBR) is electromagnetic radiation created just after the Big Bang
• CMBR can only be explained by the Big Bang theory
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