TOPIC 1 - ENERGY

Question 1

Name the energy stores.

Answer 1

Thermal 
Kinetic 
Gravitational potential
Elastic potential 
Chemical 
Magnetic 
Electrostatic 
Nuclear

Question 2

How can energy be transferred?

Answer 2

Mechanically - force, doing work
Electrically - work done by moving charges
Heating or radiation - light or sounds

Question 3

What is a system?

Answer 3

A single object eg the air in a piston or a group of objects eg two colliding vehicles that you’re interested in.

Question 4

What happens when a system changes?

Answer 4

Energy is transferred. It can be transferred into or away from the system, between different objects in the system, or between different types of energy stores.

Question 5

What is a closed system?

Answer 5

Are systems where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always zero.

Question 6

What is work done?

Answer 6

Another way of saying the energy transferred. Work can be done when current flows or by a force moving an object.

Question 7

Explain the kinetic energy store.

Answer 7

Anything that is moving has energy in its kinetic energy store. Energy is transferred to this store when an object speeds up and is transferred away from this store when an object slows down. The energy in the kinetic energy store depends on its mass and speed. The greater it’s mass and the faster it’s going, the more energy there will be in the kinetic energy store.

Question 8

What is the equation for kinetic energy?

Answer 8

Kinetic energy = 1/2 mass x speed (v) squared

Question 9

Talk about the gravitational potential energy store.

Answer 9

Raised objects store energy in the gravitational potential energy store. Lifting an object in a gravitational field requires work. This causes a transfer of energy to the gravitational potential energy store of the raised object. The higher the object is lifted, the more energy is transferred to this store. The amount of energy is a gpe store depends on the objects mass, height and the strength of the gf the object is in.

Question 10

What is the equation to find the change in energy in an object’s gravitational potential energy store?

Answer 10

Gravitational potential energy = mass x gravitational field strength x height.

Question 11

Talk about elastic potential energy stores.

Answer 11

Stretching or squashing can transfer energy to elastic potential energy stores. This is as long as the limit of proportionality has not been extended.

Question 12

What is the equation to find the energy in the elastic potential energy store?

Answer 12

Elastic potential energy = 1/2 spring constant x extension squared

Question 13

What is the specific heat capacity?

Answer 13

THE AMOUNT OF ENERGY NEEDED TO RAISE THE TEMPERATURE OF 1KG OF A SUBSTANCE BY 1 DEGREES CELSIUS.
Means how hard it is to heat something up. More energy needs to be transferred to the thermal energy store of some materials to increase their temperature than others.
Materials that need to gain lots of energy in their thermal energy stores to warm up also transfer loads of energy when they cool down again. They can ‘store’ a lot of energy.

Question 14

What is the equation for specific heat capacity?

Answer 14

Change in thermal energy = mass x specific heat capacity x temperature change.

Question 15

What is the practical to investigate specific heat capacity?

Answer 15

To investigate a solid material (eg copper) you will need a black of the material with two holes in it (for the thermometer and heater to go into)
Measure the mass of the block, the wrap it in an insulating layer (eg a think layer of newspaper) to reduce energy transferred form the block to the surroundings. Measure the initial temperature of the block and the the potential difference (V) of the power supply to be 10V. Turn on the power supply and start a stop watch. The current does work on the heater, transferring energy electrically from the power supply to the heater’s thermal energy store. This is the transferred to the material’s thermal energy store by heating, causing the materials temperature to increase.
Take readings of temperature and current every ten minutes. (The current shouldn’t change as the block heated up). Once you have collected enough readings turn off the power supply. You can calculate the power supplied to the heater using the equation power = potential difference x current. You can use this to calculate how much energy has been supplied to the heater using E = Pt. you can the plot a graph of energy transferred to the thermal energy store against temperature. Find the gradient of the straight part of the graph. The specific heat capacity is
1/(gradient x mass of the block).

Question 16

What is the conservation of energy principle?

Answer 16

Energy is always conserved. When energy is transferred between stores, not all of the energy is transferred usefully into the store. Some energy is always dissipated when an energy transfer takes place. Dissipated energy is sometimes called wasted energy because energy is being stored in a way that is not useful.
Eg in mobile phones some energy is dissipated in the transfer to the thermal energy energy store of the phone.

Question 17

What is power?

Answer 17

The rate of energy transfer, or the rate of doing work. Power is measured in watts - one watt = 1 joule of energy transferred per second.

Question 18

What are the two equations to calculate power?

Answer 18

Power = energy transferred/time

Power = work done/time

Question 19

What is conduction?

Answer 19

Conduction is the process where vibrating particles transfer energy to neighbouring particles.
It occurs mainly in solids.
Energy transferred to an object by heating is transferred to the thermal store of the object. This energy is shred across the kinetic energy stores of the particles in the object. The particles vibrate more and collide with each other. These collisions cause energy to be transferred between the particles kinetic energy stores. This is conduction.

Question 20

What is thermal conductivity?

Answer 20

A measure of how quickly energy is transferred through a material in this way. Materials with a high thermal conductivity transfer energy between their particles quickly.

Question 21

What direction is heat transfer?

Answer 21

Hot to Cold.

Question 22

What is convection?

Answer 22

Convection is where energetic particles move away from hotter to cooler regions.
It can happen in gases and liquids. Energy is transferred by heating to the thermal store of the liquid or gas. This energy is shared across the kinetic energy stores of the gas or liquids particles. As these particles are able to move, when you heat a region the particles move faster and the space between them increases. This causes the density of the region being heated to decrease. As liquids and gases can flow, the warmer and less dense region will rise above the denser, cooler regions. If there is a constant heat source, a convection current can be created.

Question 23

How do radiators create a convection current?

Answer 23

Energy is transferred from the radiator to the nearby air particles by conduction (the air particles collide with the radiator surface). The air by the radiator becomes warmer and less dense as the particles move quicker. This warm air rises and is replaced by cool air. The cooler air is then heated by the radiator. At the same ti,e, the previously heated air transfers energy to the surroundings. It cools, becomes denser and sinks. This cycle repeats, abusing a flow of air to circulate around the room - this is a convection current.

Question 24

How can lubrication reduce unwanted energy transfer?

Answer 24

Lubrication reduces frictional forces. Whenever something moves, there is usually at least one frictional force acting against it,this causes energy 8 the energy system to be dissipated eg air resistance can transfer energy from falling objects kinetic energy store to its thermal energy store. For objects that are being rubbed together, lubricants can be used to reduce friction between the objects surfaces when they move. Lubricants are usually liquids, for example oil, so they flow easily between objects and coat them.

Question 25

How does insulation reduce the rate of energy transfer by heating?

Answer 25

You can have thick walls in your home made from materials with low thermal conductivity. The thicker the walls and the lower the thermal conductivity, the slower the rate of energy transfer will be (so the building will cool more slowly).

Use thermal insulation.

Question 26

Give some example of thermal insulation in the home.

Answer 26

Cavity walls - made up of an inner and an outer wall with an air gap in the middle. The air gap reduces the amount of energy transferred by conduction through the walls. If the cavity is filled with foam, it can also reduce energy transfer by convection in the cavity.
Loft insulation can reduce convection currents being created in lofts.
Double glazed windows also have an air gap between two sheets of glass to prevent energy transfer by conduction through the windows.
Draught excluders around doors and windows reduce energy transfer by convection.

Question 27

What practical can be done to measure the effectiveness of materials as thermal insulators?

Answer 27

Boil water in a kettle. Pour some of the water into a sealable container eg a beaker and lid, to a safe level. Measure the mass of water in the container.
Use a thermometer to measure the initial temperature of the water.
Seal the conga Jed and leave it for five minutes. Measure this time using a stopwatch.
Remove the lid and measure the final temperature of the water.
Pour away the water and allow the container to cool to room temperature.
Repeat this experiment, but wrap the container in different materials eg foil, newspaper etc, once it has been sealed. Make sure you use the same mass of water each time and the same initial temperature.
The lower the temperature difference (and so energy transferred) the better that material is as a thermal insulator.
You could also investigate how the thickness of the material affects how good of a thermal insulator it is.

Question 28

What are the two equations to calculate efficiency?

Answer 28

Efficiency = useful output energy transfer/total input energy transfer.

Efficiency = useful power output/total power input.

Question 29

Give example of non-renewable energy sources.

Answer 29

Coal
Oil
(Natural) Gas

Question 30

Give example of renewable energy sources.

Answer 30

Solar 
Wind 
Water waves 
Hydro-electricity 
Bio fuel
Tides
Geothermal.

Question 31

Explain wind power.

Answer 31

Involves wind turbines in exposed places like on moons or round coasts. Each turbine has a generator - the rotating blades turn the generator and produce electricity.
There is no pollution (except for a little bit when manufactured)
They may spoil the view
Can be noisy
They only work when the wind is strong enough. So, it is impossible to increase supply when there is extra demand.
The initial costs are quite high, but there are no fuel costs and minimal running costs.
No permanent damage to the landscape.

Question 32

Explain solar cells.

Answer 32

They generate an electric current r directly from sunlight. They are often the best sources of energy to charge batteries in calculators and watches which don’t use much electricity.
They are often used in remote places where there is not much choice or to power electric road signs and satellites.
There is no pollution (although they do use quite a lot of energy to manufacture in the first place).
They are a reliable source in sunny countries - but only in the daytime.
You can’t increase the power output when there is extra demand.
Initial costs are high but after that the energy is free and running costs are low.
They are usually used to generate electricity on a relatively small scale.

Question 33

Explain geothermal energy.

Answer 33

This is possible in volcanic areas or where hot rocks lie quite near the surface. The source of much of the energy is the slow decay of various radioactive elements, including uranium, deep inside the earth.
This is free energy that is reliable, and it does very little damage to the environment.
It can be used to generate electricity, or to heat buildings directly.
However, there aren’t many suitable locations for power plants, and the cost of building a power plant is often high compared to the amount t of energy it produces.

Question 34

Explain hydro-electric power.

Answer 34

Usually requires the flooding of a valley by building a big dam. Water is allowed out through turbines. There is no pollution (as such).
However, there is a big impact on the environment caused by flooding of the valley, which may lead to a possible lack of habitat. The reservoirs can also look very unsightly when they dry up.
It can provide an immediate response to an increased demand for electricity. There is no problem with reliability except in times of drought - this is not really an issue in England.
Initial costs are high but there are no fuel costs and minimal running costs.
It can be a useful way to generate electricity on a small scale in remote areas.

Question 35

Describe wave power.

Answer 35

You need lots of small wave-powered turbines located around the coast. The moving turbines are connected to a generator.
There is no pollution, although it may disturb the sea bed and habitats of marine animals. They might also spoil the view and be a hazard to boats.
They are fairly unreliable since waves tend to die out when the wind drops.
Initial costs are high but there are no fuel costs and minimal running costs.
It is unlikely to provide enough energy on a large scale, but I can be very useful on small islands.

Question 36

Describe tidal barrages.

Answer 36

Tidal barrages are big dams build across river estuaries, with turbines in them. As the tide comes in it fills the estuary the water is then allowed out through turbines at a controlled speed.
Tides are produced by the gravitational pull of the sun and moon.
There is no pollution. However, the main problems are preventing free access by boats, spoiling the view and a,terming the habitat of the wildlife.
Tides are reliable in the sense that they happen twice a day. However, the height of the tide is variable so lower tides will produce less energy. They might not also work when the water level is the same either side of the barrage. This will happen four times a day due to the tides.
Initial costs are moderately high, but there are no fuel costs and minimal running costs. It has the ability to generate significant amounts of energy.

Question 37

What are bio-fuels?

Answer 37

They are made from plants and waste.
The are renewable.
They can be solid, liquid or gas and can be burnt to produce electricity or run cars in the same was as fossil fuels.
They are carbon neutral.
Fairly reliable, as crops grow in a short time and different crops can be grown all year round. However, they cannot respond to immediate energy demands.
The cost to refine bio-fuels is very high.
In some regions, large areas of forest have been removed to make room to grow bio-fuels the decay and burning of this vegetation also increases CO2 and methane emissions.

Question 38

How are fossil fuels cost effective?

Answer 38

Despite the set up costs of power plants being quite high, the running costs aren’t that expensive. Combined with fairly low fuel extraction costs using fossil fuels is a cost effective way to produce energy.

Question 39

How do fossil fuels create environmental problems?

Answer 39

CO2 adds to the greenhouse effect, and contributes to global warming.
Burning coal and oil also releases sulphur dioxide which causes acid rain - which can e harmful to trees and soils and can have far-reaching effects in ecosystems.
Coal mining ruins landscapes, especially “open cast mining”.
Nuclear power is clean but the nuclear waste is very dangerous and difficult to dispose of.
Nuclear power always carries the risk of a major catastrophe.