Topic 1 — Energy

What is a system?

An object or a group of objects.

What happens when a system changes?

There are changes to the way energy is stored.

What are the changes involved in the way energy is stored when an object is projected upwards?

• Kinetic energy as it goes up — it is moving quickly

• As it gets higher and slows down — kinetic energy → gravitational potential energy

• Once it reaches its highest point (and stops momentarily):

  • kinetic energy — zero

  • gravitational potential energy — maximum

What are the changes involved in the way energy is stored when a moving object hits an obstacle?

• Starts with kinetic energy

• On impact, kinetic energy = zero

• Energy is transferred to the thermal energy stores of object and obstacle

  • Makes them warmer

• Some energy is transferred to the surroundings as sound waves

What are the changes involved in the way energy is stored when an object is accelerated by a constant force?

Energy is transferred to its kinetic energy store — it speeds up

What are the changes involved in the way energy is stored when a vehicle slows down?

• Energy is transferred away from its kinetic energy store

• As brakes are applied, friction causes this energy to be transferred mechanically into the thermal energy stores of the brakes and the air (they heat up)

What are the changes involved in the way energy is stored when you bring water to a boil in an electric kettle?

• Energy is transferred electrically from the mains supply to the thermal energy store of the kettle’s metal heating element.

• Energy is then transferred by heating into the thermal energy store of the water — causes its temperature to rise until it boils.

What is the equation for kinetic energy? State the units.

kinetic energy = 0.5 × mass × (speed)²

$$E_{k}=\frac12mv^2$$

• kinetic energy — joules (J)

• mass — kilograms (kg)

• speed — metres per second (m/s)

What is the equation for elastic potential energy? State the units.

elastic potential energy = 0.5 × spring constant × (extension)²

$$E_{e}=\frac12ke^2$$

• elastic potential energy — joules (J)

• spring constant — newtons per metre (N/m)

• extension — metres (m)

What assumption do we make when using the equation for elastic potential energy?

The limit of proportionality has not been exceeded.

What is the equation for gravitational potential energy? State the units.

gravitational potential energy = mass × gravitational field strength × height

$$E_{p}=mgh$$

• gravitational potential energy — joules (J)

• mass — kilograms (kg)

• gravitational field strength — newtons per kilogram (N/kg)

• height — metres (m)

What is the typical value of gravitational field strength?

9.8 N/kg

What is the equation for the amount of energy stored in or released from a system as its temperature changes (change in thermal energy)? State the units.

change in thermal energy = mass × specific heat capacity × temperature change

$$\Delta E=mc\Delta\theta$$

• change in thermal energy — joules (J)

• mass — kilograms (kg)

• specific heat capacity — joules per kilogram per degree Celcius (J/kg°C)

• temperature change — degrees Celcius (°C)

What is the specific heat capacity of a substance?

The amount of energy required to raise the temperature of 1 kg of the substance by 1°C.

Required Practical 1 — Specific Heat Capacity (Joulemeter):

Describe a method for investigating the specific heat capacity of different metals.

Use the equation to help you: $\Delta E=mc\Delta\theta$

• Zero the balance (removes zero error) and measure the mass of the metal block.

• Wrap insulation around the block — reduces heat loss to the surroundings.

• Add a few drops of water into the thermometer hole — improves thermal contact.

• Insert the thermometer and record the initial temperature.

• Insert an immersion heater into the block, connect it to a joulemeter and power supply, and switch it on.

• Allow the block to heat up (until temperatures rise by ~15°C), then record the highest final temperature and the total energy transferred from the joulemeter.

• Use the equation: $\Delta E=mc\Delta\theta$

Required Practical 1 — Specific Heat Capacity (Voltmeter & Ammeter):

Describe a method for investigating the specific heat capacity of different metals.

Use the equation to help you: $\Delta E=mc\Delta\theta$

• Zero the balance (removes zero error) and measure the mass of the metal block.

• Wrap insulation around the block — reduces heat loss to the surroundings.

• Add a few drops of water into the thermometer hole — improves thermal contact.

• Insert the thermometer and record the initial temperature.

• Insert an immersion heater into the block, connect it to a power supply with an ammeter in series and a voltmeter in parallel across the heater, start a stopwatch, and switch it on.

• Allow the block to heat up (until temperatures rise by ~15°C), then record the highest final temperature, the current from the ammeter, the potential difference from the voltmeter, and the total time in seconds.

• Calculate the total energy transferred using $E=IVt$ , then use the equation: ΔE=mcΔθ.

What is the independent variable in RP1?

The energy supplied by the heater

What is the dependent variable in RP1?

The temperature of the material

What are the control variables in RP1?

• The mass of the block

• The power of the heater

• The insulation used

What are the sources of error in RP1 — how can they be fixed?

• Heat loss to the surroundings

  • Wrap the block in an insulator with low thermal conductivity — reduced thermal energy transferring to the air

• Poor thermal contact

  • Add a few drops of water into the thermometer hole — improves thermal contact and ensures an accurate reading

• Incomplete energy transfer

  • Make sure the immersion heater is fully inserted into the material — allows all heat to be transferred usefully

• Misreading the thermometer

  • Use an electronic temperature probe — prevents parallax errors

• A student used two different types of thermometer to measure the temperature changes for RP1.

• Figure 2 shows a reading on each thermometer.

What is the resolution of thermometer B? [1 mark]

0.1 °C

• A student used two different types of thermometer to measure the temperature changes for RP1.

• Figure 2 shows a reading on each thermometer.

Thermometer A is more likely to be misread. Give one reason why. [1 mark]

Parallax error

• A student used the apparatus drawn to investigate the heating effect of an electric heater.

• Before starting the experiment, the student drew Graph A.

• Graph A shows how the student expected the temperature of the metal block to change after the heater was switched on.

Describe the pattern shown in Graph A. [2 marks]

Temperature increase and time switched on are directly proportional.

• A student used the apparatus drawn to investigate the heating effect of an electric heater.

• Before starting the experiment, the student drew Graph A.

• Graph A shows how the student expected the temperature of the metal block to change after the heater was switched on.

• The student measured the room temperature. He then switched the heater on and measured the temperature of the metal block every 50 seconds.

• The student calculated the increase in temperature of the metal block and plotted Graph B.

• After 300 seconds, Graph B shows the increase in temperature of the metal block is lower than the increase in temperature expected from Graph A.

Suggest one reason why. [1 mark]

Energy transfer from the block to the surroundings.

• A student uses the same heater to heat blocks of different metals.

• Each time the heater is switched on for 300 seconds.

• Each block of metal has the same mass but a different specific heat capacity.

Which one of the metals will heat up the most? Give, in terms of the amount of energy needed to heat the metal blocks, a reason for your answer. [2 marks]

Metal	Specific Heat Capacity in J/kg°C
Aluminium	900
Iron	450
Lead	130

• Lead

• Needs the least energy to raise temperature by 1°C

What is power?

• The rate at which energy is transferred.

or

• The rate at which work is done.

What is the equation for power? — involving energy transferred. State the units.

power = energy transferred + time

$$P=\frac{E}{t}$$

• power — watts (W)

• energy transferred — joules (J)

• time — seconds (s)

What is the equation for power? — involving work done. State the units.

power = energy transferred + time

$$P=\frac{W}{t}$$

• power — watts (W)

• work done — joules (J)

• time — seconds (s)

An energy transfer of 1 _______ _____ _________ is equal to a power of 1 ____.

• joule per second

• watt

What are the eight different energy stores?

• Thermal

• Kinetic

• Gravitational potential

• Elastic potential

• Chemical

• Magnetic

• Electrostatic

• Nuclear

What is meant by a thermal energy store?

The total kinetic and potential energy of the particles in an object.

What are some examples of thermal energy stores? (3)

• Human bodies

• Hot coffees

• Stoves

What is meant by a kinetic energy store?

The energy a system has because it is moving.

What are some examples of kinetic energy stores? (3)

• Runners

• Buses

• Comets

What is meant by a gravitational potential energy store?

The energy a system has because of how high above the ground it is.

What are some examples of gravitational potential energy stores? (3)

• Aeroplanes

• Kites

• Mugs on a table

What is meant by a chemical energy store?

The energy stored in chemical bonds.

What are some examples of chemical energy stores? (3)

• Food

• Fuels

• Batteries

What is meant by an elastic potential energy store?

The energy stored in a system when it is stretched or squashed.

What are some examples of elastic potential energy stores? (3)

• Drawn catapults

• Compressed springs

• Inflated balloons

What is meant by a thermal energy store?

What is meant by a magnetic energy store?

The energy stored when two repelling magnetic poles have been pushed together or two attracting magnetic poles have been pulled apart.

What are some examples of magnetic energy stores? (2)

• Fridge magnets

• Compasses

What is meant by an electrostatic energy store?

The energy stored when repelling charges have been moved closer together or attracting charges have been pulled apart.

What are some examples of electrostatic energy stores? (2)

• Thunderclouds

• Van De Graaff generators

What is meant by a nuclear energy store?

The energy stored in the nucleus of an atom.

What are the four ways energy can be transferred?

• Mechanical

• Electrical

• Heating

• Radiation

What is meant by the mechanical energy transfer pathway?

• Energy is transferred mechanically when a force is used to move an object a certain distance.

• This is called the work done by the force.

What is meant by the heating energy transfer pathway?

Energy is transferred by heating when there is a temperature difference — so energy flows from a hotter area to a colder area.

What is meant by the electrical energy transfer pathway?

• Energy is transferred electrically when a charge flows around a circuit.

• This is called the work done when an electrical current flows.

What is meant by the radiation energy transfer pathway?

Energy is transferred by radiation when it is transferred by waves or particles.

• In a ride at a theme park, a person is strapped into a pod that is attached to two stretched bungee cords.

• The bungee cords behave like springs.

• The figure shows a person using the ride.

Which energy store increases as the bungee cords are stretched? [1 mark]

Elastic potential

• A fire piston is a special type of syringe that can be used to start fires.

• Figure 2 shows a fire piston.

• The plunger is pushed quickly downwards and compresses the air.

• When the air is compressed quickly, the temperature of the air increases.

How does an increase in temperature affect the air particles inside the piston? [1 mark]

The mean kinetic energy of the particles increases.

What is the law of conversation of energy?

Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.

• In all system changes energy is ___________, so that it is stored in less ________ ways.

• This energy is often described as being ‘________’.

• dissipated

• useful

• wasted

How does a pendulum show the conservation of energy?

• At its highest point of its swing it has maximum gravitational potential energy.

• As it falls it gains kinetic energy which is its greatest at the mid part of its swing.

• As it moves past the midpoint it decreases in kinetic energy and increases again in gravitational potential energy.

What energy transfers happen to a bungee jumper after jumping off the platform?

• When the rope is slack, energy is transferred — _____________ __________ energy store → _________ energy store as the jumper _____________ towards the ground (due to the force of ________).

• When the rope tightens, it ________ the jumper’s fall — the force of the rope reduces the _________ of the jumper.

• Jumper’s __________ energy store decreases, rope’s __________ ____________ energy store increases as rope ____________.

• Eventually the jumper comes to a stop — energy in __________ energy store of the jumper all transferred to the ___________ __________ energy of the rope.

• After reaching the bottom, rope recoils and pulls jumper back up — as jumper rises energy in ___________ ___________ energy store of rope decreases and jumper’s ___________ energy store increases (until rope becomes ________).

• After rope becomes ________ (and at the top of the ascent), jumper’s __________ energy store = 0 — jumper’s ______________ __________ energy store increases through the ascent.

• gravitational potential

• kinetic

• accelerates

• gravity

• slows

• speed

• kinetic

• elastic potential

• stretches

• kinetic

• elastic potential

• elastic potential

• kinetic

• slack

• slack

• kinetic

• gravitational potential

What happens when there are energy transfers in a closed system?

There is no net change to the total energy.

What are two ways to reduce unwanted energy transfers?

• Lubrication

• Thermal insulation

How can lubrication reduce unwanted energy transfers?

• Oil/grease can be used — slightly separates moving parts

• Reduces friction when objects rub against each other

• Decreases the amount of energy wasted as heat to the surroundings

How can thermal insulation reduce unwanted energy transfers?

• Uses materials with low thermal conductivity — e.g. double glazing or loft insulation

• Often works by trapping pockets of air — very poor thermal conductor

• Slows down the rate of energy transfer — reduces the amount of useful thermal energy lost from a system

The higher the __________ _________________ of a material the higher the rate of energy transfer by ______________ across the material.

• thermal conductivity

• conduction

What is the rate of cooling of a building affected by?

• Thickness of its walls

• Thermal conductivity of its walls

How is the rate of cooling of a building affected by the thickness and thermal conductivity of its walls?

• Higher thermal conductivity of the walls = higher rate of energy transfer — building will cool down faster

  • Using materials with low thermal conductivity slows down this heat loss

• Thicker walls reduce the rate of thermal energy transfer — lowers the rate of cooling

What is the independent variable in RP 2 (Activity 1)?

Type of insulating material

What is the independent variable in RP 2 (Activity 2)?

Thickness of material

What is the dependent variable in RP 2?

Temperature decrease over time

What are the control variables in RP 2 (Activity 1)?

• Volume of water

• Initial temperature of the water

• Thickness of the insulation

What are the control variables in RP 2 (Activity 2)?

• Volume of water

• Initial temperature of the water

• Type of insulating material

Describe a method for investigating the effectiveness of different materials as thermal insulators. (6)

• Place a small beaker inside a larger beaker and pack the gap with an insulating material — leave one setup with no insulator as a control

• Pour a fixed volume of hot water into the small beaker

• Place a cardboard lid on top with a thermometer placed through a hole

• Record the initial temperature (this should be the same for each material) and start a stopwatch

• Record the temperature every 3 minutes for 15 minutes

• Calculate the total temperature drop for each material (initial temperature - final temperature) — the one with the lowest value is the best thermal insulator

• This graph shows results for the practical investigating the effectiveness of different materials as thermal insulators.

What does this graph show? (4)

• The curve which takes the longest time for the water temperature to drop (the shallowest) should be the material that is the best insulator.

• The temperature falls quickly at high temperatures and slowly at low temperatures.

• When the beaker is at a high temperature, there is a big difference between the temperature of the beaker and the temperatures of the surrounding air — this means that there is a high rate of transfer.

• When the beaker is at a lower temperature, there is less difference between the temperature of the beaker and the temperatures of the surrounding air — this means that there is a lower rate of transfer.

Describe a method for investigating how the thickness of a material affects the thermal insulation. (6)

• Wrap a beaker in a single layer of an insulator — e.g. newspaper

• Pour a fixed volume of hot water into the beaker

• Add a cardboard lid and insert a thermometer into the water

• Record the initial temperature (this should be the same for each round of the experiment) and start a stopwatch

• Record the temperature every 3 minutes for 15 minutes

• Repeat the experiment, adding more layers of the same material — compare the overall temperature drops (initial temperature - final temperature)

• This graph shows results for the practical investigating how the thickness of a material affects the thermal insulation.

What does this graph show? (5)

• The curve which takes the longest time for the water temperature to drop (the shallowest gradient) shows the amount of layers that provide the best insulation.

• The curve for no insulation has the steepest gradient at any given time interval.

• As the number of layers increases, the gradient of each curve decreases at any given time interval.

• Having more layers increases the insulation which means temperature drops more slowly — the thickest insulation has the lowest rate of cooling.

• The temperature falls quickly at high temperatures and slowly at low temperatures.

What is the equation for the energy efficiency for any energy transfer (energy)?

efficiency = (useful output energy transfer / total input energy transfer) × 100

What is the equation for the energy efficiency for any energy transfer (power)?

efficiency = (useful power output / total power input) × 100

What are the main energy resources? (9)

• Fossil fuels

  • coal

  • oil

  • natural gas

• Nuclear fuel

• Bio-fuel

• Wind

• Hydroelectricity

• Geothermal

• Tidal power

• Solar power

• Water waves

Which of the main energy resources are renewable?

• Bio-fuel

• Wind

• Hydroelectricity

• Geothermal

• Tidal power

• Solar power

• Water waves

Which of the main energy resources are non-renewable?

• Fossil fuels

  • coal

  • oil

  • natural gas

• Nuclear fuel

What is a renewable energy resource?

One that is being (or can be) replenished as it is used.

What do the uses of energy resources include? (4)

• Transport

• Electricity

• Generation

• Heating

Which gas in coal contributes to acid rain?

Sulfur dioxide

Which fossil fuels can be fired up the quickest to meet spikes in demand?

Oil and gas

What is the effect of sulfur dioxide on the environment?

Causes acid rain

How does solar power improve a hydroelectric system's reliability?

It provides power when hydroelectric power output is low — e.g. in summer.

• Three energy sources used to generate electricity are given in List A.

• Statements about the energy sources used to generate electricity are given in List B.

Match each energy source in List A to the statement about the energy source in List B. [3 marks]

• 1 — B

• 2 — A

• 3 — D

• In the UK, most electricity is generated in power stations that burn fossil fuels.

Which type of fossil fuel power station has the shortest start-up time? [1 mark]

Gas

• Decreasing the amount of carbon dioxide released by different activities will help slow down climate change.

• Transport and generating electricity are the two activities that released the largest amounts of carbon dioxide in the UK in 2018.

Explain one change that would reduce the amount of carbon dioxide released by each activity. [4 marks]

• Transport

  • don’t use petrol cars for transport

  • use electric cars instead

• Generating electricity

  • don’t use fossil fuels to generate electricity

  • use renewable methods instead

• A remote village in the UK uses a hydroelectric generator to provide electricity.

• The hydroelectric generator is turned by falling river water.

• Figure 2 shows how the power output of the hydroelectric generator varied during one year.

Explain one reason why the power output varied. [2 marks]

• The amount of rainfall varies

• And is lower in the summer months

What are the advantages of coal? (3)

• Reliable

• Cheap

• Relatively high energy per kg

What are the disadvantages of coal? (4)

• Long startup time

• Non-renewable

• Finite

• Releases greenhouse gases

What is the environmental impact of coal? (3)

• It releases carbon dioxide — contributes to global warming and climate change

• It releases sulfur dioxide (impurities) — causes acid rain (destruction to wildlife)

• It releases carbon particulates — cause breathing difficulties and global dimming

What are the advantages of oil? (4)

• Can be fired up quickly to meet demand

• Reliable

• High energy density

• Cheap

What are the disadvantages of oil? (3)

• Non-renewable

• Releases greenhouse gases

• Finite

What is the environmental impact of oil? (2)

• It releases carbon dioxide — contributes to global warming and climate change

• It releases dangerous pollutants (diesel) — can harm health

What are the advantages of natural gas? (4)

• Shortest startup time

• Burns cleaner than coal — less carbon dioxide

• Reliable

• Relatively cheap

What are the disadvantages of natural gas? (3)

• Non-renewable

• Releases greenhouse gases

• Finite

What are the environmental impacts of natural gas?

It releases carbon dioxide — contributes to global warming and climate change

What are the advantages of nuclear fuel? (3)

• Very high energy density

• No greenhouse gas emissions

• Suitable for base load

What are the disadvantages of nuclear fuel? (6)

• Long startup time

• Radioactive waste must be stored for thousands of years

• Non-renewable

• Risk of accidents

• Expensive

• Slow to decommission

What is the environmental impact of nuclear fuel? (2)

• Produces radioactive waste — could release radioactive compounds into the environment

• Doesn’t release carbon dioxide