Energy

Question 1

What is a system? Explain an open, closed and isolated system.

Answer 1

A system is an object or group of objects.
Open system allows the exchange of energy and matter to and from its surroundings.
Closed system can exchange energy but not matter to and from its surroundings.
Isolated system does not allow the transfer of energy or matter to or from its surroundings.

Question 2

What are the different stores of energy?

Answer 2

Kinetic, Gravitational Potential, Elastic Potential, Magnetic, Electrostatic, Chemical, Nuclear, thermal

Question 3

What are the descriptions of each of these energy stores?

Question 4

What are the 4 different energy transfer pathways and what are their descriptions?

Answer 4

Mechanical work - when a force acts on an object (e.g. pushing, pulling, stretching, squashing)
Electrical work - A charge moving through a potential difference (e.g. current)
Heating (by particles) - Energy is transferred from a hotter object to a colder one (e.g. conduction)
(heating by) Radiation - Energy transferred by electromagnetic waves (e.g. visible light)

Question 5

What is the principle of the conservation of energy?

Answer 5

Energy cannot be created or transferred, it can only be transferred from one store to another.
Energy can be transferred usefully, stored or dissipated, but cannot
be created or destroyed.
Therefore, in a closed system, the total amount of energy stored is constant.

Question 6

For the following examples, name the initial and final energy stores as well as the method responsible for transferring energy from the initial to the final store:
a. the sun heating up the earth
b. A travelling bullet hitting a target
c. A burger being cooked on a charcoal barbecue

Answer 6

a. nuclear store to thermal store by radiation
b. kinetic store to thermal store by mechanical work
c. chemical store to thermal store by heating

Question 7

Describe the changes in the way energy is stored in a petrol car accelerating from rest to a velocity of 60mph on a level road. Assume no energy is lost to the surroundings.

Answer 7

chemical store of energy stored in the petrol is transferred to kinetic energy store in the engine by (mechanical) work, transferred to the kinetic energy store of the moving car by (mechanical) work.

Question 8

Describe the changes in the way energy is stored for an elastic band that is stretched and fired vertically upwards. Assume no energy is lost to the surroundings.

Answer 8

Chemical energy in person is transferred to elastic potential energy in the stretched elastic band by (mechanical) work. When the band is initially fired, the elastic potential energy in the band is transferred to the kinetic energy store of the band by (mechanical) work. As the elastic band gains height, kinetic energy is transferred to gravitational potential energy of the band by (mechanical) work.

Question 9

Describe the changes in the way energy is stored for a pole vaulter, starting at rest, accelerating, then using a bendy pole to get over a high bar.

Answer 9

chemical energy in person is transferred to kinetic energy by work as the person is running, which is transferred to elastic potential energy of the pole vault as it bends (by mechanical work), and as the pole vaulter gains height, the elastic potential energy is transferred to gravitational energy by mechanical work.

Question 10

What is the equation for kinetic energy?

Answer 10

Ek = 1/2 mv^2 (KE = half * mass * velocity squared)

Question 11

What is the equation for elastic potential energy?

Answer 11

Ee = 1/2 ke^2 (EPE = half * spring constant N/m * extension squared m)

Question 12

What is the equation for gravitational potential energy?

Answer 12

Ep = mgh (GPE = mass * gravitational field strength * (change in) height)

Question 13

How do you calculate the amount of energy stored in or released from a system as its temperature changes?

Answer 13

change in thermal energy = mass x specific heat capacity x temperature change (^E = mc^0) (J = kg x J/kg*C x *C)

Question 14

What is the heat capacity of an object?

Answer 14

Heat capacity of an object is the energy needed per degree of heating. Measured in J/*C

Question 15

What is the specific heat capacity of an object?

Answer 15

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

Question 16

How much energy is needed to heat up 1kg of water by 15 degrees? (C = 4.186 or 4.2)

Answer 16

63KJ

Question 17

What is internal energy?

Answer 17

Internal energy is the total energy stored by the particles making up a substance or a system. It is the total potential and kinetic energy.

Question 18

A material with higher specific heat capacity requires more energy to change its temperature. True or false

Answer 18

True

Question 19

A beaker of water with a mass of 250g was heated until its internal energy increased by 21 kJ.

If the water’s original temperature was 24 °C, what is its final temperature?
(Specific heat capacity of water is 4,200 J/kg°C)

Answer 19

44 degrees Celsius

Question 20

To heat 20g of aluminium by 1*C requires 18 J of energy. To heat the same amount of gold only requires 2.6 J.

Which element must have higher specific heat capacity?

Answer 20

Aluminium

Question 21

A lump of gold with a mass of 20g was heated to 53 °C, and then allowed to cool down to 28 °C.

If gold’s specific heat capacity is 130 J/kg°C, how much internal energy did it lose in the cooling process?

Answer 21

65J

Question 22

Describe a method used to determine the specific heat capacity of one or more materials, using the following pieces of equipment:
1kg copper, iron and aluminium blocks each with two holes
Thermometer
Pipette
30W heater
12V power supply
Insulation
Stopwatch
Balance
Heatproof mat

Question 23

What is the definition of power?

Answer 23

Power is defined as the rate at which energy is transferred or the rate at which work is done.

Question 24

What is the unit of power

Answer 24

Watts

Question 25

What is the relationship between work done and energy transferred?

Answer 25

Work done = energy transferred (both are in Joules) So, 1 Joule/second = 1 Watt

Question 26

What is the equation for power?

Answer 26

power = energy transferred / time
power = work done / time

Question 27

What happens to dissipated energy?

Answer 27

It is lost to the surroundings

Question 28

As a bowl of hot porridge cools down, what happens to the energy in its thermal energy store?

Answer 28

It is dissipated to its surroundings.

Question 29

State the method used for required practical 2.

Question 30

What is the equation for efficiency?

Answer 30

efficiency = useful output energy transfer /total input energy transfer

efficiency = useful power output / total power input

little tip - answer cannot be over 1 or over 100%

Question 31

An electric current delivers a power of 60 watts to a lightbulb. 3 watts of electrical energy are transferred to the lightbulb. Calculate the efficiency of the bulb.

Answer 31

5%

Question 32

Describe ways to increase the energy transfer when heating water over the stove/boiling it in an electric kettle.

Answer 32

1. Use a lid - so less thermal energy is being passed into the air.
2. Use a pan with a wider base - so less thermal energy from the hob is passing into the air. Rather, it is passing through the base of the pan.
3. Place the heating element inside the pan (like in an electric kettle) as a lot of thermal energy is used from heating the pan.
4. Place plastic walls around the metal pan (like in an electric kettle) so less thermal energy escapes to the surroundings through the sides as plastic is a good thermal insulator and metal is a good thermal conductor.

Question 33

What is the definition of efficiency?

Answer 33

Efficiency is the fraction of the energy supplied to a device that is used usefully. The remainder is wasted energy.

Question 34

What is a big cause of wasted energy and what can you do to help it?

Answer 34

Friction is often the cause of wasted energy: transfers kinetic energy into thermal energy. Lubrication with oil or grease, reducing friction, helps a lot.

Question 35

What are the main energy sources available for use on Earth?

Answer 35

non renewable:
Fossil fuels (coal, oil and gas), nuclear fuel
Renewable:
Bio-fuel
Wind power
Water power (wave/hydro-electric/tidal)
solar power
geothermal

Question 36

What is a renewable energy source?

Answer 36

A renewable energy source is one that is being (or can be) replenished as it is used. (aka will never urn out).

Question 37

What are the uses of energy sources?

Answer 37

Transport, electricity generation and heating.

Question 38

What is an energy store?

Answer 38

An energy store is a way in which energy can be kept in a system.

Question 39

What is an energy system?

Answer 39

Systems that can store large amounts of energy are called energy sources.

Question 40

Electricity can be generated using various energy sources. Give one advantage and one disadvantage of using nuclear power stations rather than gas-fired power stations to generate electricity.

Answer 40

Advantage:
little carbon dioxide goes into the atmosphere
longer operating life
higher energy density in fuel
Disadvantage:
radioactive waste
decommissioning costs
accidents at nuclear power stations may have far reaching or long term effects
long start up time

Question 41

Explain the process/workings of a typical power plant.

Answer 41

Fuel is burnt in a furnace (can be coal, oil, gas, biofuel etc.) Chemical energy of coal converted to thermal/kinetic energy of water - steam.
Water heated to produce high pressure steam.
Hot wasted gas leaves.
Steam pushes around a turbine, which is like a giant fan.
The turbine is attached to a generator and makes the generator spin. the generator transforms kinetic energy into electrical energy.
Electricity goes out to all dem homes.
Steam cooled in cooling tower and condensed in water to be reused again.

Question 42

What is bio-energy, what are its advantages and disadvantages?

Answer 42

Biomass is palnt and animal matter, such as wood, straw, sewage and waste food. The power we produce from biomass is called bio-energy.
Advantages:
cheap
helps get rid of waste, which can cause smells and pollution
It is not using up limited resources like coal: biomass cannot run out.

Disadvantages:
Burning the fuel creates carbon dioxide (unless you grow plants that absorb the same amount of CO2 - effect is less harmful)
Collecting waste in big enough amounts to generate electricity can b difficult
If trees aren’t grown especially for fuel, and replanted, the result is deforestation

Question 43

What is geothermal energy, what are its advantages and disadvantages?

Answer 43

The deeper you dig, the hotter it gets. This is because of the natural heat that exists deep within the Earth. We call this natural heat, or geothermal energy.

Advantages:
geothermal energy doesn’t produce any pollution.
running costs for a geothermal power station are very low

disadvantages:
difficult to find suitable sites for geothermal power stations - hot rocks have to be a suitable type and depth
If not carefully managed, a borehole can “run out of steam” and may not be useable again for several decades
occasionally dangerous gases and minerals can come out of a borehole and it may be difficult to dispose of them.

Question 44

What is hydro-electricity, what are its advantages and disadvantages?

Answer 44

When we use the energy in flowing water to produce electricity, we call it hydroelectricity.

Advantages:
once construction is completed, the operating costs are very low.
Now waste or pollution is produced
Electricity can be generated constantly, because water can be stored and used as needed
Disadvantages:
Dams are very expensive to build
Hydroelectricity sites are often remote, which leads to higher distribution costs
Suitable sited for large scale projects are hard to find

Question 45

What are hydrogen fuel cells, what are its advantages and disadvantages?

Answer 45

A hydrogen fuel cell works like a battery, but it uses hydrogen to make electricity. In other words, it converts hydrogen to electrical power.
Advantages:
there’s no pollution - the only waste product is water and some heat, which can also be reclaimed.
There’s no noise
Fuel cells can be built in a huge range of sizes to suit almost any use
Fuel cells rely on hydrogen which has to be made. Most of the methods we use to produce hydrogen today use a lot of non-renewable energy, but this could change
It will be some time before hydrogen is as freely available as petrol is now
Hydrogen is flammable but there are systems we can use to allow safe use

Question 46

What is solar energy, what are its advantages and disadvantages?

Answer 46

Solar energy is energy from the sun. Each minute of the day, the sun delivers enough energy to meet global demand for a whole year.
Advantages
Once the solar power plant is constructed, running costs are very low
Solar energy can be used to generate electricity in remote places
No waste or pollution is produced
Energy is usually generated at or near where it will be used, keeping transmission and distribution costs to a minimum
It doesn’t work at night
Photovoltaic (PV) cells are very expensive (but they are getting cheaper)

Question 47

What is wind energy, what are its advantages and disadvantages?

Answer 47

Wind is created because some parts of the Earth get more heat than others.
Advantages:
once the turbine is built, running costs are very low
no waste or pollution is produced
the land occupied by a wind farm can still be used for farming
wind farms can become tourist attractions
Disadvantages:
no wind, no power
some people object because they feel wind farms spoil the view
wind farms create a constant low-level noise
they can interfere with television reception and radar

Question 48

What is tidal energy, what are its advantages and disadvantages?

Answer 48

Around the coast of the UK, the sea levels rise and fall twice daily. Tis rising and falling of the sea is caused by the pull of the moon.
Advantages:
Running costs are very low
No waste or pollution is produced
The technology is very reliable
no fuel is required
The amount of electricity and the time when it is produced is totally predictable
Disadvantages:
There are only a few suitable places for tidal energy projects
Tidal stream technology is at a very early stage of development
Tidal schemes are expensive to install compared with other renewable energies
damming bays or inlets can affect the environment over a large area
Barrage schemes will only provide energy for about 10hours each day, as the tide moves in and out.