Physics Revision (P1)

Almost 75% of the electricity made in the UK comes from fossil fuels. These are:

• Coal
• Oil
• Natural gas

Fossil fuels are a non-renewable source of energy, meaning they are being used up faster than they can be made. This means they will eventually run out.

Coal and oil release sulfur dioxide when combusted (burned), which contributes to acid rain and can cause breathing problems for people.

Fossil fuels release carbon dioxide when combusted. This adds to the greenhouse effect and contributes to global warming.

Coal releases the most carbon dioxide, and natural gas releases the least amount of carbon dioxide.

The two main nulclear fuels are uranium and plutonium. Both of these are radioactive metals.

Remember that nuclear fuels are not burnt to release energy. Nuclear fission reactions in the fossil fuels release thermal (heat) energy.

Advantages

• Nuclear fuels do not produce sulfur dioxide or carbon dioxide.

Disadvantages

• Nuclear fuels are a non-renewable energy resource.
• Radioactive, therefore, hazardous to health.

Wind is produced by huge convection currents in the Earth's atmosphere.

They are driven by heat evergy from the Sun.

Kinetic energy produced by the wind is a renewable energy resource.

'Wind turbines use the wind to drive the turbines directly. They have huge blades mounted on a tall tower.'

'As the wind blows, it transfers some of its kinetic energy to the blades, which turn and drive the generator.'

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/mains/generatingelectricityrev3.shtml

Advantages

• Renewable
• No harmful gases produced.

Disadvantages

• Noisy
• Not good to look at - they spoil the view ------> Visual pollution
• The amount of electricity generated all depends on how fast the wind is. No wind, no electricity.

Wave: The water in the sea rises and falls because of waves on the surface.Wave machines use the kinetic energy in this movement to drive electricity generators.

Tides: Huge amounts of water move in and out of river mouths due to tides.

A tidal barrage is a barrier built over a river estuary to make use of the kinetic energy in the moving water.

The barrage contains electricity generators, which are driven by the water rushing through tubes in the barrage.

Hydroelectric power: Hydroelectric power stations use kinetic energy in moving water. But the water comes from behind a dam.

The water high up behind the dam contains gravitational potential energy. This is transferred to kinetic energy as the water rushes down through tubes inside the dam.

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/mains/generatingelectricityrev4.shtml

Advantages

• Renewable
• No fuel costs
  
• Tidal barrages and hydroelectric power stations are very reliable and it is very easy to switch them on.
  

Disadvantages

• Flood the farmland
• Destroy estuary species' habitat
• Rotting vegetation releases methane ( a greenhouse gas)
  

Hot water and steam from deep under the ground can be used to drive turbines: this is known as geothermal energy

In volcanic areas, the rocks heat the water, and the steam naturally rises to the surface

Advantages

• renewable energy resource
  
• no fuel costs
• No harmful polluting gases are produced

Disadvantages

Most parts of the world do not have suitable areas where geothermal energy can be exploited.

Solar energy is energy collected from the cell.

Advantages

• Renewable
• No fuel costs
• No harmful polluting gases
• Solar cells provide electricity in remote areas

Disadvantages

• Expensive
• Inefficient - no Sunlight, no electricity, therefore, do not work at night
  

Chemical energy stored in fuel. Energy is released when chemical reactions take place.

Kinetic energy is the energy of a moving object

Gravitational potential energy  is the energy of an object because of its position

Elastic (strain) energy is the energy stored in springy items when we stretch or squash them

Electrical energy is the energy transferred by an electric current

Thermal (heat) energy is energy due to its temperature. This is partly because of the random kinetic energy of particles.

We say energy is transformed when it changes from one form into another.

CONSERVATION OF ENERGY: energy can never be created, nor be destroyed, but can be changed from one form to another.

Conduction

• Metals conduct heat better than non-metals
• Copper is better at conducting heat than steal
• Wood conducts heat better than glass
• Conduction in a metal is due mainly to free electrons transferring inside the metal
• Non-metals are poor conductors because they do not contain free electrons.
• Materials such as fibreglass are good insulatord because they contain pockets of trapped air.

Convection

• Convection takes place only in liquids and gases (fluids).
• Heating a liquid or gas makes it less dense.
• Convection is due to a hot liquid or gas rising.
• It takes place due to convection currents within the fluid.

Radiation

• All objects give out thermal radiation.

• Dark, matt surfaces are better emitters of thermal radiation than light, shiny surfaces.
• Dark, matt surfaces are better absorbers of thermal radiation than light, shiny surfaces.

• Loft insulation such as fibreglass reduces heat loss through the roof. Air between the fibres also helps to reduce hear loss by conduction.

• Aluminium foil between a radiator panel and the wall reflects heat radiation away from the wall.

• A double glazed window has two glass panels with dry or a vacuum between the panes. Dry air is a good insulator so it cuts down heat conduction. A vacuum cuts out heat transfer by convection as well.

• Cavity wall insulation reduces heat loss through the walls. We place insulation between the two layers of brick that make up the walls of a house.

A vacuum flask will keep a hot liquid hot in the winter. The same flask will keep cold liquids cold in the summer.

The liquid is in the double-walled glass container:

• The vacuum between the two walls of the container cuts out heat transfer by conduction and convection between the walls.
• Glass is a poor conductor so there is little heat conduction through the glass.
• The glass surfaces are silvery to reduce radiation from the outer wall.
• The case surrounding the flask provides additional insulation.

Useful energy is energy transferred to where it is wanted in the form it is wanted.

Wasted energy is energy is energy that is not usefully transferred or transformed.

Wasted energy spreads out to the surroundings.

Energy becomes less useful, the more it spreads out.

Weight is measured in Newtons (N).

Energy is measured in Joules (J).

Energy supplied = useful energy delievered + energy wasted

Efficiency = useful energy transferred by the device / total energy supplied by the devices

U-values

U-values measure the effectiveness of a material as an insulator in buildings.

The lower the U-value is, the better the material is as a heat insulator.

Payback time

payback time (years) = cost of installation (£) ÷ savings per year in fuel costs (£)

Temperature and heat are not the same thing:

• temperature is a measure of how hot something is
• heat is a measure of the thermal energy contained in an object.

Temperature is measured in °C, and heat is measured in J. When heat energy is transferred to an object, its temperature increase depends upon the:

• the mass of the object
• the substance the object is made from
• the amount energy transferred to the object.

The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1 kg of the substance by 1°C.

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/heatingandcooling/buildingsrev3.shtml

Here is the equation relating energy to specific heat capacity:

E = m × c × θ

• E is the energy transferred in joules, J
• m is the mass of the substances in kg
• c is the specific heat capacity in J / kg °C
• θ (‘theta’) is the temperature change in degrees Celsius, °C

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/heatingandcooling/buildingsrev3.shtml

power (W) = energy transferred (J) / time taken (s)

the more powerful a device is, the faster thr rate at which it transforms energy.  

energy transferred (kWh) = power (kW) × time (h)

total cost = number of units × cost per unit

Transformers

Transformers are used in the National Grid. A transformer is an electrical device that changes the voltage of an alternating current (ac) supply, such as the mains electrical supply. A transformer that:

• increases the voltage is called a step-up transformer - change the voltage to the very values needed to transmit electricity through the National Grid power lines.
• decreases the voltage is called a step-down transformer - used locally to reduce the voltage to safe levels.

Electricity from a power station goes to:

1. step-up transformers
2. high voltage transmission lines
3. step-down transformers
4. consumers, for example homes, factories and shops.

Underground or Overground?

Underground cables would be:

• much more expensive
• much more difficul to repair
• difficult to bury when they cross canals, rivers and roads.

Electomagnetic waves are electric and magnetic disturbances that transfer energy from one place to another.

Wave speed (m/s) = frequency (Hz) x wavelength (m)

You can use the formula triangle above to get the formula for frequency and wavelength as well as wave speed.

'Waves are vibrations that transfer energy from place to place without matter (solid, liquid or gas) being transferred.'

Transverse Waves

The oscillations are at right angles to the direction of travel and energy transfer.

Longitudinal Waves

The oscillations are along the same direction as the direction of travel and energy transfer.

Refraction

'Sound waves and light waves change speed when they pass across the boundary between two substances with different densities, such as air and glass.

This causes them to change direction and this effect is called refraction.'

Diffraction

'When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap.

This is called diffraction.'

The theory says that at the start, all the matter in the universe was concentrated into a single incredibly tiny point.

This began to get bigger rapidly in a hot explosion (called the Big Bang), and it is still expanding today.

The Big Bang happened about 13.7 billion years ago.

CMBR (Cosmic Microwaves Background Radiation)

• It was created as high-energy gamma radiation just after the Big Bang happened.
• It has been travelling through space since the Big Bang.
• As the Universe has expanded, it stretched out to longer abd longer wavelengths and is now microwave radiation.
  

When a source moves towards an observer, the observed wavelength decreases and the frequency increases.

When a source moves away from an observer, the observed wavelength increases and the frequency decreases.

Astronomers have found that the further from us a star is, the more its light is red-shifted. This means that the light moves towards the red end of the electromagnetic spectrum.

This tells us that distant galaxies are moving away from us, and that the further away a galaxy is, the faster it's  moving away.