4.1 Energy

Question 1

a system

Answer 1

an object or a group of objects working together
when a system changes, there are changes in the way energy is stored; an electric kettle transfers electrical energy to thermal energy

Question 2

changes involved in the way energy is stored when a system changes; an object projected upwards
(kicking a ball up in the air)

Answer 2

mechanical work done
(work done is another way of saying energy transferred)

The initial force by the person to kick a ball upwards does work. Causes an energy transfer from the chemical energy store from their leg to to kinetic energy store of the ball.

Question 3

10 forms of energy

Answer 3

magnetic, kinetic, thermal, light, gravitational potential, chemical, sound, elastic potential, electrical, nuclear

energy is transferred mechanically, electrically, heating, or by radiation

Question 4

changes involved in the way energy is stored when a system changes; a moving object hitting an obstacle (Work done when force moves an object)

Answer 4

eg. a car hitting a wall , mechanical
Initially the car is moving, the initial store of energy is kinetic energy. It then hits the wall, stops. The energy is stored as thermal energy (and sound)

Question 5

changes involved in the way energy is stored when a system changes; an object accelerated by a constant force

Answer 5

Work is done by a force on an object. This work (chemical) is converted to the object’s kinetic store.
mechanical

Question 6

changes involved in the way energy is stored when a system changes; a vehicle slowing down

Answer 6

mechanical
friction between car’s brakes and wheels does work as it slows down. Causes an energy transfer from car’s kinetic energy stores to thermal energy store of the brakes (and sound)

Question 7

changes involved in the way energy is stored when a system changes; bringing water to boil in an electrical kettle

Answer 7

electrical energy in the kettle increases thermal energy of the kettle and the water -> causing temperature of the water to rise

Question 8

calculating kinetic energy of a moving object

Answer 8

Ek (joules) = 0.5 x mass(kg) x speed² (m/s)

Ek = 0.5mv²

Question 9

calculating elastic potential energy stored in a stretched spring

Answer 9

elastic potential energy (joules) = 0.5 x spring constant(N/m) x extension² (m)

Ee = 0.5 ke²

Question 10

calculating gravitational potential energy gained by an object raised above ground level

Answer 10

g.p.e (joules) = mass (kg) x gravitational field length (N/kg) x height (m)

Ep = mgh

Question 11

calculating the amount of energy stored in or released from a system as its temperature changes

Answer 11

change in thermal energy = mass (kg) x specific heat capacity (J/kg°C) x temperature change (°C)

∆E = mc∆θ

Question 12

heat capacity

Answer 12

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 Celsius

Question 13

RP 1 : investigation to determine the specific heat capacity of one or more materials (method)

Answer 13

1. (1kg) copper, iron and aluminium blocks (each with two holes, one for heater, one for thermometer)
2. Place thermometer and immersion heater in the block (add water if needed to increase thermal contact -> air gap)
3. Wrap it in an insulating layer to reduce thermal energy transfer to surroundings
4. Record initial temperature of the block. Turn on power supply and start a stop watch. Measure temp of block every 10 minutes
5. Calculate the power by measuring current and potential difference (p = IV). Use this to calculate the energy transferred to the heater (E=Pt (time in seconds)

When you turn on the power, the current in the circuit, does work on the heater, transferring energy electrically from the power supply, to heater’s thermal energy store.
This energy is then transferred to the material’s thermal energy store by heating -> material’s temperature increases

6. Plot a graph of temperature against work done by the heater. Calculate gradient of the line.
7. specific heat capacity = gradient / mass of block
8. Can repeat experiment with different materials to see how their specific heat capacities compare

Question 14

RP 1 : investigation to determine the specific heat capacity of one or more materials (variables, safety precautions, sources of inaccuracy)

Answer 14

Variables
independent variable - type of material
dependent variable - the temperature
control variables - mass of material used and energy provided

Safety precautions
Don’t handle the block or heater whilst or after heating
Keep block on heatproof mat
Take care not to spill water near power supply, clean up spills immediately

Sources of inaccuracy (specific heat capacity calculated may not be accurate)

• thermal energy passing out of beaker to surroundings
• > use insulator with low thermal conductivity
• incorrect reading of thermometer -> use electronic temperature probe

Question 15

Power

Answer 15

Power is the rate at which energy is transferred or the rate at which work is done

power (watts) = energy transferred (joules)/ time(seconds)
P = E/T

or

power (watts) = work done (joules)/time (seconds)
P = W/T

An energy transfer of 1 joule per second is equal to a power of 1 watt
(A 60 watt light bulb, for example, transfers 60 joules of energy every second)

Question 16

Explain how two systems transferring the same amount of energy can differ in power output due to the time taken

Answer 16

If given two motors A and B, the motor that can do the same work faster is more powerful – as the
energy is transferred at a faster rate.

Question 17

Conservation of energy principle

Answer 17

energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed
Only some of the energy in a system is usefully transferred, the rest is ‘wasted’ (in all systems, energy is dissipated, so it’s stored in less useful ways)

Example
for a radio or set of speakers, the electrical work is transferred into useful sound and infrared radiation is dissipated – ie wasted as heat energy

Question 18

Reducing wasted energy caused by unwanted energy transfers

Answer 18

• lubrication -> reduces the friction that produces heat
  (oil in a motor)
• tightening any loose parts -> prevents unwanted vibration that wastes energy as sound
• thermal insulation -> reduces heat loss
  (double glazing)

Question 19

closed systems

Answer 19

The term “closed system” refers to something where nothing can get in or out – including energy.
In a closed system, the total energy never changes, but it can be transferred from one energy store to another.

Example:
A cold spoon is dropped into an insulated flask of hot soup, which is then sealed. Assume that the flask is a perfect thermal insulator, so the spoon and the soup is a closed system. Energy is transferred from the thermal energy store of the soup to the useful energy store of the spoon, causing the soup to cool down slightly. Although energy transfers have occurred within the system, no energy has left the system -> net change in energy is zero

Question 20

Thermal conductivity

Answer 20

The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across the material. (, heat is allowed to travel through the
material more easily)

Question 21

Thermal conductivity in a building

Answer 21

The rate of cooling of a building is affected by the thickness and thermal conductivity of its walls
(If the walls are thin metal sheets, heat would be lost very quickly. )
(Rate of cooling is low if walls are thick and thermal conductivity of the walls are low also double glazed windows)

Question 22

RP 2: Investigating the effectiveness of different materials as thermal insulators and investigating factors that may affect the thermal insulation properties of a material. (1)

Answer 22

Method 1 - Testing different types of materials

1. Set up your equipment, and wrap 4 of the 5 beakers with a different insulating material (use rubber bands to secure the insulation)
2. The beaker with no insulation wrapped around it is the control beaker
3. Cut circles of cardboard to form lids for each container (with a hole in the middle for the thermometer)
4. Fill each beaker with hot water from a kettle and record the initial temperature of each beaker.
5. Start stopwatch and measure the temperature of the beakers every 3 minutes for 15 minutes
6. Calculate the change in temperature for each beaker (initial temperature - final temperature)

Variables
Independent variable - type of insulating material
dependent variable - temperature
control variable - volume of water and thickness/mass of insulating material

Question 23

RP 2: Investigating the effectiveness of different materials as thermal insulators and investigating factors that may affect the thermal insulation properties of a material. (2)

Answer 23

Method 2 - Testing different thicknesses of insulator

1. Wrap 5 beakers in varying thicknesses of one insulating material; wrap each beaker in newspaper using one more sheet per beaker
2. Fill each beaker with hot water, record initial temperature and cover each beaker with cardboard lids
3. Measure temperature of the beakers every 3 minutes
4. Record results and calculate the change in temperature for each beaker

Variables
independent variable - the number of layers of newspaper
dependent variable - temperature
control variable - starting temperature of water and volume of water

Question 24

RP 2: safety precautions and errors

Answer 24

• don’t handle beaker whilst or after heating
• keep beakers on a heatproof mat

errors
- cooling curve should be a smooth curved line, if there is an anomaly, it will not fit the pattern of the curve and should be ignored

Question 25

Efficiency

Answer 25

The efficiency of a system is the proportion of energy that ends up in the intended from.

Efficiency = useful output energy transfer ÷ total input energy transfer

or

efficiency = useful power output ÷ total power input

Question 26

Ways to increase the efficiency of an intended energy transfer

Answer 26

• Reducing waste output (lubrication, thermal insulation, etc.)
• Recycling waste output (e.g. absorbing thermal waste and recycling as input energy)

Question 27

Main renewable and non-renewable energy resources

Define what a renewable energy resource is

Answer 27

non-renewable = fossil fuels (coal,oil,gas), nuclear fuel, peat
eventually will run out
renewable = bio-fuel, wind, hydro-electricity, geothermal, the tides, the Sun (solar) and water waves

A renewable energy resource is one that is being (or can be) replenished as it is used. They have become more important due to the finite lifetime of fossil fuels -> their development has become more important

Question 28

Uses of energy resources

Answer 28

transport, electricity generation and heating
Non-renewable resources can produce large amounts of energy because of the large energy output per kg of fuel -> renewable resources can’t

Question 29

reliable energy source

Answer 29

A reliable energy resource is one that can produce energy at any time.
Non-reliable resources can only produce energy some of the time (e.g. when it’s windy).

Renewable energy is not always the most reliable -> solar doesn’t work in bad weather or night, wind is only intermittent

Question 30

energy in transport

Answer 30

non renewable

• petrol and diesel powered vehicles use fuel created from oil
• coal is used in some old fashioned steam trains to produce steam

renewable
- vehicles that run on pure bio fuel or a mix of biofuel and petrol/diesel

Question 31

energy in heating

Answer 31

non-renewable

• natural gas is the most widely used fuel to heat homes in the UK
• coal is commonly burnt in fireplaces
• electric heaters

renewable

• geothermal heat pump uses geothermal energy resources to heat buildings
• solar water heaters
• burning bio-fuel or using electricity generated from renewable resources

Question 32

advantages of the majority of renewable energy resources

Answer 32

don’t release CO2, we are never going to run out of them, generally non-polluting

solar and wind directly generate electricity with no emissions

Question 33

disadvantages of renewable energy resouces

Answer 33

solar - expensive to install, doesn’t work in bad weather, or during the night
wind turbines - some people don’t like them, don’t work very well on non windy days
tidal and wave power - disruptive to local environment
hydro electric dam involves flooding a large area (may include people’s homes or animal habitats)
geothermal - can only be used in volcanic countries

Question 34

advantages of non renewable energy resources

Answer 34

very readily available, very cheap source of electricity, things like coal power stations have a short start up time

Question 35

disadvantages of non renewable energy resources

Answer 35

coal, oil, gas - take millions and millions of years to create, heavily polluting -> release large amounts of CO2 and other pollutants into the atmosphere -> contributes to climate change
- coal mining makes a mess of the landscape
nuclear fuel- produces dangerous radioactive waste that can take thousands of years to decay (Small risk of explosion)
- oil spillages cause serious environmental problems -> affecting mammals and birds living in and around the sea

Question 36

Patterns and trends in the use of energy resources

currently we still depends on fossil fuels

Answer 36

• Fossil fuels became an important source of energy during the Industrial Revolution as it was easy to mine and provided lots of energy
• Since the 21st century, the start of the 21st century, electricity use in the UK has decreased, due to making out appliances more efficient and be more careful with energy use in our homes.
• most of the electricity is generated using fossil fuels and nuclear power
• However, we are trying to increase our use of renewable energy resources

Question 37

patterns and trends in the use of energy resources

people want to use more renewable energy resources

Answer 37

• people want to use more renewable energy resources that affect the environment less, as fossil fuels are very damaging to the environment
• people & governments are aware that non-renewables will run out one day, better to learn to live without them before this happens
• pressure from other countries & public, government has introduced targets for using renewable resources
• car companies -> electric cars and hybrids are already on the market and popularity is increasing

carbon neutral energy resources either lack public support, reliability or cannot produce sufficient energy to meet our needs.

Question 38

patterns and trends in the use of energy resources

the use of renewables is limited due to reliability, money and politics

Answer 38

• lots of scientific evidence to support the use of renewables, but scientists can’t force the public or governments to change their behaviour
• building renewable power plants cost money ->energy providers are reluctant, fossil fuels are cost effective
• arguments about where to put the new power plants, many people don’t want to live next to a wind farm, arguments about if it’s ethical
• some energy resources like wind power are not as reliable, and others cannot increase their power output on demand (whereas fossil fuels can)
• research on improving the reliability and cost of renewables takes time and money -> until then we need non renewable & dependable power
• making personal changes can be expensive
• > solar panels for homes and hybrids are usually more expensive than equivalent petrol cars

Question 39

steps towards cleaner technologies over the past 20 years

Answer 39

• Government grants have encouraged the development of wind and solar farms.
• Coal has gradually been replaced with cleaner natural gas.

Question 40

work done equation

Answer 40

work done (joules) = force (N) x distance (m)