Physics Revision

Circuits

2012-08-26T16:30:00.001-07:00

Circuits

Series circuit are one loop. There is only one way for the electrons to flow.

The current – how many electrons pass a point each second.

Voltage – The difference in energy carried by an electron between two points.

The ammeter counts the current.

The current is measured in amps (A) and the voltage is measured in Volts (V).The voltage is always the same and the current is different. The ammeter on top of the battery should equal the same as the ammeter on the first light bulb and the second light bulb.

Electrons are given energy as they pass through a cell or battery. We can measure the energy given to an electron by the cell or battery using a voltmeter.

Generation on Electricity and Renewable Fuels

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Generation of Electricity

The power stations turn the coal, crude oil and the natural gas which is chemical potential energy into electrical energy. Most of the power we use at home is generated at power stations. In the UK, we mainly use Coal and Gas as our source of energy (fuel).

The fuel is burned to release its chemical energy. The heat energy released is used to boil water and turn it into steam. The energy is now thermal energy. The steam then turnes the turbines. The turbines then turn large generators. The energy is currently kinetic energy. The generators then produce electrical energy.

Renewable Fuels

Solar Power, Wind Power, Tides, Biomass, Hydroelectric and Geothermal.

Solar Power – Solar Power stations use concave mirrors to focus the suns energy on a boiler. The water boils and produces steam. This steam turns the turbine, which turns the electricity generator which prouces electricity.

It is renewable and cheap to run once built. Solar cells are expensive and contains toxic chemicals. It is low power and unreliable.

Wind Power – The wind turns a turbine which then turns the electricty generator. The generator then produces electricity.

It is renewable, no acid rain, cheap to run once built, doesnt effect global warming. It is unreliable, expensive, kills birds, low power and few suitable areas.

Hydroelectric – The water turns the turbine using kinetic energy. The turbine then turns the generator which then produces electricity.

No acid rain and does not effect global warming, energy efficient and cheap to run once built. Expenisve to build, few areas suitable and low power.

Waves – The moon produces the waves. The waves turn the turbines, generating electricity.

Renewable, no acid rain, doesnt effect global warming. Energy efficient and cheap to run once built. Expensive to build, low power and few areas suitable.

Tidal – The moon causes the tides, the tides go up and down which turns the turbines.

It is renewable and its non polluting but its expensive and low power.

Biomass – Burns organic matter to make steam turn a turbine.

It is renewable and grows more plants. Needs a large area and destroys habitats.

Fossil Fuels

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Fossil Fuels

The three fossil fuels are:

Coal
Crude Oil
Natural Gas

All energy on the Earth comes from the sun. Plants store the suns energy through photosynthesis. Animals then eat the plants and then we eat the animals as food.

Fossil fuels are formed from plants and animals that died over 100 million years ago. When they died they became covered with many layers of mud and earth. The resulting large pressures and high temperatures changed them into fossil fuels. Because they take millions of years to form these fossil fuels, they are called non-renewable fuels. Once they have been used up they cannot be replaced.

Coal – millions of years ago the plants photosynthesised and stored the suns energy. Dead plants fall into swampy water and the mud stopped them rotting away. The mud piles up and squashes the plants. After millions of years the mud becomes rock and the plants become coal. To get the coal, miners have to dig down shafts and tunnels. There is probably enough coal for only 300 more years.

Crude Oil and Natural Gas – Tiny animals live in the sea, when they die, they fall into the mud and dont rot away. Over millions of years they are burried deeper by the mud and sand. The pressure changes mud and sand into rock and the animals become oil and gas. The oil and gas are trapped below the rock. We can drill down to get it but oil will only last another 40 more years.

Energy

2012-08-26T16:18:00.001-07:00

Energy

Energy Transfers

The eight different types of energy are:

Kinetic Energy

Elastic Potential Energy

Thermal Energy

Gravitational Potential Energy

Electrical Energy

Chemical Potential Energy

Light Energy

Sound Energy

Energy in	Energy Changer	Energy Out
Chemical (food)	Animal	Heat, Kinetic, Chemical
Stored potential energy	Bow and Arrow	Kinetic
Chemical	Battery	Electrical
Electrical	Battery Charger	Chemical
Electrical	Electic Motor	Kinetic
Kinetic Energy	Generator	Electrcial
Gravitational Potential	Falling Object	Kinetic

GCSE Physics Revision

2012-08-26T14:46:00.002-07:00

GCSE Physics Revision

Section One - Heat and Energy
Moving and Storing Heat

Heat is a measure of Energy. When a substance is heated, its particles gain energy. This energy makes the particles in a gas or liquid move around faster. In a solid, the particles vibrate more rapidly.

This energy is measured on an absolute angle. (This means it cant go lower than zero, because there’s a limit to how slow particles can move. The unit of thermal energy is measured in Joules (J).

Temperature is a measure of Hotness. The hotter something is, the higher its temperature. Temperature is usually measured in °C (degrees Celsius), but there are other temperature scales, like °F (degrees Fahrenheit).
Energy tends to flow from hot objects to cooler objects - e.g. warm radiators heat the cold air in your room. The bigger the temperature difference, the faster the heat is transferred. If theres a difference in temperature in tow different places, then energy will flow between them.

Specific heat capacity tells you how much energy stuff can store. It takes more heat energy to increase the temperature of some materials than others - e.g. you need 4200 joules to warm 1kg of water by 1 degrees but only 139 joules to warm 1kg of mercury by 1 degrees.
Materials which need to gain lots of energy to warm up also release loads of energy when they cool down again. They can store a lot of heat.

The measure of how much energy a substance can store is called its specific heat capacity. Specific heat capacity is the amount of energy needed to raise the temperature of 1kg of a substance by 1 degrees - e.g. water has a specific heat capacity of 4200J/kg°C.
The specific heat capacity of water is high, once water is heated, it stores lots of energy, which makes it good for central heating systems. Also, waters a liquid so it can be pumped around a building easily.
Energy = Mass x Specific Heat Capacity x Temperature Change
Example: How much energy is needed to heat 2kg of water from 10°C to 100°C? Answer: Energy needed = 2 (Mass) x 4200 (SHC) X 90 (Temp Change) = 756 000J
Mass x Temp Ch 0.2 x 105

Example: An empty 200g aluminium kettle cools down from 115°C to 10°C, loosing 19 068 J of thermal energy. What is the
specific heat capacity of aluminium.
Answer: SHC = Energy = 19 068 = 908J/kg°C

Section One - Heat and Energy
Melting and Boiling

If you heat up water on a stove, the water will never get hotter than 100°C. You can carry on heating the water up, but the temperature won’t rise.
You need to put in Energy to break Intermolecular Bonds. When you heat a liquid, the heat energy makes the particles move faster. Eventually, when enough of the particles have enough energy to overcome their attraction to each other, big bubbles of gas form in the liquid - this is boiling.

In a solid, heat energy makes the particles vibrate faster until eventually the forces between them are overcome and the particles start to move around - this is melting. When a substance is melting or boiling, you’re still putting in energy, but the energy’s used for breaking intermolecular bonds rather than raising the temperature. (There are very good graphs about this on the page before).

When a substance is condensing or freezing, bonds are forming between particles, which releases energy. This means the temperature doesn’t go down until all the substance has turned into a liquid (condensing) or a solid (freezing).
Specific latent heat is the energy needed to change state. The specific latent heat of melting is the amount of energy needed to melt 1kg of material without changing its temperature. The material’s got to be at its melting temperature already.

The specific latent heat of boiling is the energy needed to boil 1kg of material without changing its temperature. The material’s got to be at its boiling temperature already.
Specific latent heat is different for different materials, and its different for boiling and melting. There is a formula:
Energy = Mass x Specific Latent Heat
Example: The specific latent heat of water (for melting) is 334 000 J/kg. How much energy is needed to melt an ice cube of mass 7g at 0°C.
Answer: Energy = 0.007 x 334 000 J = 2338
Example: The specific latent heat of water (for boiling) is 2 260 000J/kg.
2 825000J of energy is used to boil a pan of water at 100°C. What was the mass of water in the pan?
Answer: Mass = Energy = 2 825 000 = 1.25kg
SLC 2 260 000

Section One - Heat and Energy
Conduction and Convection

Conduction is most important in Solids. Houses lose a lot of heat through their windows even when they’re shut. One reason for this is that heat flows from the warm inside face of the window to the cold outside face by conduction.
In a solid, the particles are held tightly together. So when one particle vibrates, it bumps into other particles nearby and quickly passes the vibrations on.

Particles which vibrate faster than others pass on their extra kinetic energy to particles nearby. These particles then vibrate faster themselves. This process continues throughout the solid. This causes a rise in temperature at the other side.

Conduction of Heat is the process where vibrating particles pass on their extra kinetic energy to nearby particles.

Metals are really good conductors of heat and non metals are really good for insulating things. Liquid and gases conduct heat more slowly than solids - the particles aren’t held so tightly together. So air is a good insulator.

Convection occurs in Liquids and Gases. When you heat up a liquid or gas, the particles move faster, and the fluid (liquid or gas) expands, becoming less dense. The warmer, less dense fluid rise above its colder, denser surroundings, like a hot air balloon does.
As the warm fluid rises, cooler fluid takes its place. As this process continues, you actually end up with a circulation of fluid (convection current). This is how immersion heaters work.

Convection occurs when more energetic particles move from a hotter region to a cooler region - and take their heat energy with them.

Radiators in the home rely on convection to make the warm air circulate round the room.
Convection can’t happen in solids because the particles can’t move - they just vibrate on the spot.

To reduce convection, you need to stop the fluid moving. Clothes, blankets and Cavity wall foam insulation all work by trapping pockets of air. The air cant move so the heat has to conduct very slowly through the pockets or air, as well as the material in between.
Example: If you left a spade out in the cold, the metal bit will feel colder than the wooden because the metal conducts heat away from your hand quicker but if you left the spade in the cold it will feel hotter as it conducts heat into your hand quicker.