Physics

What are the eight different energy stores?

1. Thermal energy stores

2. Kinetic energy stores

3. Gravitational potential energy stores

4. Elastic energy stores

5. Chemical energy stores

6. Magnetic energy stores

7. Electrostatic energy stores

8. Nuclear energy stores

What is chemical energy?

Energy stored in chemical bonds such as those between atoms and molecules

What are examples of chemical energy?

Food, petrol and batteries

How do you increase chemical energy?

More of the substance

What is thermal energy?

Energy stored in a warm object

What are examples of thermal energy?

Tea, radiator and coffee

How do you increase thermal energy?

Increase the heat in the warm object

What is kinetic energy?

The energy stored in a moving object

What are examples of kinetic energy?

Bike, cheetah and tennis ball

How do you increase kinetic energy?

Move the object faster or make it heavier

What is nuclear energy?

Energy stored in atoms

What are examples of nuclear energy?

Nuclear bomb, nucleus and nuclear power plant

How to increase nuclear energy?

More radioactive atoms

What is electrostatic energy?

The energy stored between 2 seperated electric charges that are attracting or repelling

What are examples of electrostatic electricity?

Hair and balloon

What is gravitational potential energy?

The energy stored by an object that is raised off the ground

What are examples of gravitational potential energy?

Anything thats raised off the ground

How to increase gravitational potential energy?

Raise it higher or add more mass

What is elastic potential?

The energy that is stored in an elastic object that is stretched or compressed

What is a system?

A group of interacting, interrelated, on independent parts that work together to form a complex, unified whole`

What happens when a system changes?

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

What is a closed system?

Systems where matter and energy cannot enter or leave.

What is the net change in total energy for a closed system?

Zero

What energy transfers take place when water is heated in an electric kettle?

Energy is transferred electrically to the thermal energy store of the kettles heating element. Energy is then transferred to the waters thermal energy store by heating.

What is work done? Can you name two ways that work can be done?

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

Describe the energy transfers that occur when a ball is dropped from a height

Energy is transferred from the gravitational potential energy store of the ball to its kinetic energy store.

Describe the energy transfers that occur when a car slows down using its breaks

Energy is transferred from the wheels kinetic energy store to the thermal energy store of the surroundings

Describe the energy transfers that occur when a car hits a stationary object

Energy is transferred from the kinetic energy store if the car to eg. the elastic potential and thermal energy stores of the car and the object

What is the formula used to calculate the energy stored in kinetic energy stores?

E_k = ½mv²

What is the formula used to calculate the energy stored in gravitational energy stores?

E_p = mgh

What is the formula used to calculate the energy stored in elastic potential stores?

E_e = ½ke²

What is the specific heat capacity of a substance?
And what is the formula for energy transferred that involves specific heat capacity?

The specific heat capacity is the amount of energy needed to raise the temperature of 1 kg of a substance by 1 °C.

∆E = mc∆θ.

Describe a method you can use to find the specific heat capacity of a material.

• Measure the mass of a block with two holes in it, then wrap it in an insulating layer.
• Insert a thermometer and a heater into the two holes and connect up the circuit.
• Measure the initial temperature of the block and set the potential difference (p.d.) of the power supply to 10 V.
• Switch on the power supply and start a stopwatch.
• Take readings of the temperature and the current (using an ammeter) every 1 minute for 10 minutes.
• Use the p.d. and the current to calculate power with P = VI. Use the power to calculate the energy transferred for each time using E = Pt.
• Plot a graph of temperature against energy transferred. The specific heat capacity is equal to 1 ÷ (gradient × mass of the block).

Describe the energy transfers that take place between a power supply, a heater and a material when measuring a material’s specific heat capacity.

The power supply causes a current to flow, and the current does work on the heater, causing energy to transfer electrically from the power supply to the heater’s thermal energy store. This energy is then transferred to the material’s thermal energy store by heating.

Give the conservation of energy principle. Give an example of it for a closed system.

Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed. E.g. a cold spoon dropped in an insulated flask of hot soup is a closed system. Energy from the thermal energy store of the soup is transferred to the thermal energy store of the spoon. This is dissipated energy as it is ‘wasted’ but no energy has been created or destroyed in the transfer.

What is meant by dissipated energy? Give an example of energy being dissipated.

It is any energy that isn’t transferred usefully. E.g. In a mobile phone, some of the energy is dissipated to its thermal energy store. Energy is then transferred from the thermal energy store of the phone to the energy store of the surroundings.

What is meant by power? Give two formulas for power involving time.

Power is the rate of energy transfer (or the rate of doing work).
Power = energy transferred ÷ time (P = E ÷ t) or power = work done ÷ time (P = W ÷ t).

How can you tell which of two identical buses with different engines is more powerful?

Over the same distance, the bus with the more powerful engine will travel faster than the bus with the less powerful engine.

Describe how energy is transferred in conduction.

One object gets heated on one side, causing the particles to vibrate and collide with one another. The collisions cause energy to be transferred between the particles’ kinetic energy stores. This process continues until the energy is transferred to the kinetic energy stores of the particles on the other side of the object.

How are materials with a high thermal conductivity different to ones with a low thermal conductivity?

Materials with a high thermal conductivity allow energy to be transferred between their particles a lot quicker than materials with a low thermal conductivity.

Describe what happens in the process of convection. What states of matter does it happen in?

Energy is transferred to the thermal energy stores of the substance being heated. This energy is then shared amongst the particles’ kinetic energy stores. The density of the heated part of the substance decreases as particles move away from one another. The warmer, less dense regions rise above denser, cooler regions. This happens in liquids and gases only.

How do convection currents form?

A constant heat source heats particles causing them to rise and get replaced by cooler particles. The cooler particles are heated, whilst the warmer particles cool back down and sink again. This cycle repeats causing a convection current.

Describe how each of the following can help to thermally insulate a house loft insulation

Reduces convection currents created in the loft.

Describe how each of the following can help to thermally insulate a house cavity walls

The air gap in the cavity wall reduces the amount of energy transferred by conduction through the walls. When the wall is filled with cavity wall insulation, it can also reduce energy transfer by convection in the wall cavity.

Describe how each of the following can help to thermally insulate a house draught excluders

Reduces energy transfers by convection around doors and windows.

Describe how each of the following can help to thermally insulate a house double glazed windows

An air gap between two sheets of glass reduces energy transfer by conduction through the windows.

Why does having walls that are thicker and made from materials with a lower thermal conductivity help to reduce energy losses from a home?

The thicker the walls and the lower their thermal conductivity, the slower the rate of energy transfer will be, which will reduce energy lost from the home.

Give a method that could be used to investigate how effective a material is as a thermal insulator.

• Measure the mass of some hot water in a container.
• Measure the initial temperature of the water with a thermometer.
• Seal the container and wait five minutes.
• Remove the lid and measure the final temperature of the water.
• Pour away the water and let the container cool to room temperature.
• Repeat the experiment (with the same mass and initial temperature of water) by wrapping the container in a different material to see how the material affects the temperature change of water.

How do lubricants reduce the amount of energy being dissipated?

Lubricants coat objects, reducing the frictional forces between their surfaces as they move over each other. This reduces the amount of energy that is dissipated.

What is the efficiency of a device?

A measure of the proportion of energy that is transferred usefully.

Give three ways that the efficiency of an energy transfer can be increased.

By insulating objects, by lubricating them or by making them more streamlined.

How can efficiency be calculated using energy transfers? How about with power input and output?

Efficiency can be calculated by dividing the useful output energy transfer by the total input energy transfer. It can also be calculated by dividing the useful power output by the total power input.

Write down four examples of non‑renewable energy resources. What are some pros and cons of non‑renewable energy resources?

Coal, oil, natural gas and nuclear fuels. They are a reliable source of energy. However, they will all run out one day and they cause a lot of damage to the environment.

List the seven types of renewable energy resources.

The Sun (solar), wind, water waves, hydro‑electricity, bio‑fuel, tides, geothermal.

Give two pros and two cons of using renewable energy resources.

Pros:
• The damage caused to the environment is less severe.
• They will never run out.

Cons:
• Most resources still cause some damage to the environment.
• Some are unreliable as they depend on the weather so it’s harder to produce as much energy on demand.

Describe three ways energy resources can be used for transport.

• Petrol and diesel powered vehicles use fuel created from oil.
• Vehicles can run on a mixture of bio‑fuels and petrol or diesel, or even pure bio‑fuels.
• Electricity generated using renewable or non‑renewable energy resources can be used to power vehicles.

Now describe six ways they can be used for heating.

• Natural gas can be used to heat water, which is then pumped into radiators.
• Coal can be burnt in fireplaces.
• Burning bio‑fuels can also be used to heat homes.
• Electric heaters can use electricity generated from renewable or non‑renewable energy resources.
• Geothermal heat pumps use geothermal energy to heat buildings.
• Solar water heaters use the Sun to heat water which is then pumped into radiators in buildings.

Where are the most suitable places to put wind turbines?

In exposed places like on moors, around coasts or at sea.

What are the advantages and disadvantages of using wind power?

Advantages:
• No pollution.
• No permanent damage to the landscape.
• No fuel costs and minimal running costs.

Disadvantages:
• Views can get spoiled.
• Can be very noisy for those nearby.
• Initial costs for making them are quite high.
• Turbines will stop turning if winds are too weak or too strong-unreliable
• Supply cannot be increased with demand.

What kinds of devices are solar cells useful for? And what kinds of places is solar power useful in?

Devices which don’t use much electricity such as calculators or watches. Solar power is useful in remote areas where there isn’t much other choice, and in places where it’s sunny a lot of the time.

What are four issues with using solar power?

Issues:
• Only produce energy in the daytime.
• Lots of energy used to manufacture the panels.
• Supply can’t be increased with demand.
• Initial costs of manufacture and set up are high.

Where does the energy for geothermal power come from?
Give two pros and two cons of using geothermal energy.

It comes from the slow decay of various radioactive elements deep inside the Earth.

Pros:
• Reliable source of free energy, since it doesn’t depend on the weather.
• Does very little damage to the environment.

Cons:
• Not many suitable power plant locations.
• Cost of building a geothermal power plant is high compared to the amount of energy produced.

How can hydroelectric power be used to meet changes in demand for electricity?
What are two other advantages of using it?

The flow of water can be controlled. Other advantages: e.g. there’s no pollution / there’s no fuel costs.

How does flooding a valley for hydroelectric power cause damage to the environment?
Give two more disadvantages of using hydroelectric power.

Flooding a valley can cause vegetation to rot, which releases methane and CO₂. It can also lead to loss of habitats.

Other disadvantages: e.g. initial costs to build the power plant are high / they can look unsightly when reservoirs dry up.

What are two advantages and four disadvantages of using wave power?

Advantages:
• No pollution.
• No fuel costs.

Disadvantages:
• Initial building and installation costs are quite high.
• Turbines are difficult and expensive to maintain.
• Can disturb habitats, spoil views and be a hazard to boats.
• Can be unreliable when the wind drops.

What are tidal barrages and how do they work?

They are big dams built across river estuaries, with turbines in them. As the tide comes in, it fills up the estuary. The water is then allowed out through turbines at a controlled speed.

What are four advantages of using tidal barrages?

• No pollution once they’re up and running.
• Tides are reliable as they always happen twice a day.
• No fuel costs and minimal running costs.
• Has the potential to generate a lot of energy.

When do tidal barrages produce less energy? Give two other disadvantages of using them.

They will produce less energy when the high tides are small. They also don’t work when water levels are the same either side of the barrage. Other disadvantages are:
• Dams prevent free access to boats, can alter habitats of wildlife and spoil the views.
• There aren’t many suitable locations.

What are bio‑fuels made from? Why is there debate around whether bio‑fuels are carbon neutral?

They are made from plant products or animal dung. Bio‑fuels are only carbon neutral if you keep growing plants at the same rate that you’re burning them.

Explain what makes bio‑fuels reliable. What are four disadvantages of using bio‑fuels?

The crops take a relatively short time to grow and can be grown all year round.
Disadvantages:
• Cost to refine bio‑fuels is high.
• Growing bio‑fuel crops means there is less space and water to grow other crops.
• Areas of forest can be cleared to grow them, destroying natural habitats.
• The decay and burning of vegetation increases CO₂ and methane emissions.

What makes using fossil and nuclear fuels relatively cost‑effective?

Many suitable power plants are already built and set up, running costs aren’t that expensive and fuel extraction costs are fairly low.

How does burning fossil fuels contribute to global warming?
Give two negative impacts of global warming.

It releases CO₂, which is a greenhouse gas. Global warming causes rising sea levels and loss of habitats.

Give the cause and impact of acid rain

Cause: Burning coal and oil releases sulfur dioxide.

Impact: Harmful to trees, soil and ecosystems.

Give the cause and impact of visual pollution

Cause: E.g. Coal mining and power plants.

Impact: Makes a mess of the landscape and spoils the view.

Give the cause and impact of oil spillages

Cause: Accidents with tankers, pipelines or oil rigs.

Impact: Affects animals that live in and around the sea.

Give the cause and impact of radiation exposure to humans and animals

Cause: Radioactive nuclear waste is hard to dispose of safely, and nuclear catastrophes can release radiation.

Impact: Radiation can be very dangerous to all living things.

a) What caused electricity use in the UK to increase in the 20th century?
b) What has caused electricity use in the UK to decrease slowly at the start of the 21st century?

a) The population grew and people started using electricity for more things.
b) Appliances have become more efficient and people have become more careful when using energy in their homes.

Give two reasons that governments might introduce targets for using more renewable resources. How does this put pressure on energy providers?

Pressure from other countries and the public. Energy providers risk losing business and money if they don’t build new renewable power plants to keep up with the government targets.

Suggest how the push for increased use of renewable energy resources has impacted car companies.

It has caused an increase in the popularity of electric cars and hybrids, affecting the types of cars that car companies develop and produce.

How does the reliability of renewable energy resources limit their use?

Many renewable resources are weather dependent and the power output of most renewables can’t be increased on demand. Switching completely to renewables would mean using a combination of different power plants or researching ways to improve reliability. Both of these options are difficult and expensive.

What are three ways in which costs limit the use of renewable energy resources?

• Cost of switching to renewable power has to be paid for by customers or the government.
• Research into improving reliability takes time and money.
• Making personal changes (e.g. buying hybrid or electric cars) can be expensive, and isn’t an option for some people.

What is meant by current, potential difference and resistance in a circuit? What are their units?

Current — flow of electrical charge. It’s measured in amperes, A.
Potential difference — the driving force that pushes charge around a circuit. It’s measured in volts, V.
Resistance — anything that slows down a flow of charge. It’s measured in ohms, Ω.

a) What causes current to flow around a closed loop?
b) True or false? Current has the same value everywhere in a single, closed loop.

a) A source of potential difference.
b) True.

For a given potential difference, how does an increase in resistance affect the current?

It causes a decrease in the current.

How is the size of an electric current related to the rate of flow of charge?

The size of the current is the rate of flow of charge.

What is the equation that links current, charge and time? What are the units for each term?

Charge flow = current × time (or Q = It)
The units for charge flow are coulombs, C. The units for current are amperes, A. The units for time are seconds, s.

You’ll need something to draw on for this question. Draw the circuit symbols for a cell, battery, open switch, closed switch, filament lamp, fuse, LED, resistor, variable resistor, ammeter, voltmeter, diode, LDR and thermistor.

What is the equation that links potential difference, current and resistance?

Potential difference = current × resistance (or V = IR)

What are ammeters and voltmeters used for? How should they each be connected in a circuit?

Ammeters measure the current flowing through a component. Voltmeters measure the potential difference across a component.
An ammeter must be connected in series with whatever you’re investigating. A voltmeter must be connected in parallel with whatever you’re investigating.

Explain how you would investigate how the length of a wire affects its resistance.

• Connect a battery/power supply, a switch, an ammeter and two crocodile clips (next to each other) in series. Attach a voltmeter across the crocodile clips.
• Attach a test wire along a metre ruler, and connect one clip to the test wire at the 0 cm mark.
• Connect the second clip to the test wire and measure the length of test wire between the clips.
• Close the switch, then record the current through the wire and the pd across it.
• Open the switch, then move the second clip along the wire. Close the switch again, then record the new length, current and pd.
• Repeat for different lengths of the test wire.
• Calculate the resistance for each length of wire, using R = V ÷ I.
• Plot a graph of resistance against wire length and draw a line of best fit.

What would you expect the results of this experiment to show?

The longer the wire, the greater the resistance.

What is an ohmic conductor? What two things are directly proportional for ohmic conductors (at a constant temperature)?

A conductor with a resistance that doesn’t change with the current flowing through it. The current flowing through an ohmic conductor at a constant temperature is directly proportional to the pd across it.

Why does the current through a filament lamp affect its resistance?

When current flows through a filament lamp, the moving charges transfer energy to the thermal energy stores of the filament, causing it to heat up. Increasing the current make the filament heat up more and more. Resistance increases with temperature, so the increase in current causes an increase in resistance.

What is an I‑V characteristic?

A graph that shows how the current flowing through a component changes as the potential difference across it is increased.

What is the difference between a linear component and a non‑linear component?

Linear components have an I‑V characteristic that is a straight line, while non‑linear components have a curved I‑V characteristic.

Describe and explain the I‑V characteristic of a fixed resistor at a constant temperature

The I‑V characteristic is a straight line through the origin. This is because a fixed resistor at a constant temperature is an ohmic conductor, so the current through it is directly proportional to the pd across it.

Describe and explain the I‑V characteristic of a diode

The I‑V characteristic is a straight line along the pd axis for all negative values of pd and positive pds below a certain value. At this value, the graph curves rapidly upwards. This is because current will only flow through a diode in one direction. The diode has very high resistance in the reverse direction.

Describe and explain the I‑V characteristic of a filament lamp

The I‑V characteristic is a curve that passes through the origin and curves towards the pd axis as the magnitude of current increases. This is because increases in current lead to increases in the temperature of the filament, so the resistance increases. This means less current can flow per unit pd, so the graph gets shallower.

Describe how you could use a standard test circuit to find the I‑V characteristic for a resistor.

• Set up a circuit with a power supply, variable resistor, ammeter and the resistor you’re testing connected in series. Attach a voltmeter in parallel with the test resistor.
• Turn on the power supply, and record the current through and pd across the test resistor.
• Vary the variable resistor, and record the new current and pd.
• Repeat this for many different values of pd and current.
• Swap the wires connected across the battery to reverse the direction of the current. Take a number of recordings for different negative currents and pds.
• Plot a graph of current against pd to show your results — this is the I‑V characteristic.

How would the circuit need to change for you to investigate the I‑V characteristic of a diode?

You would need to add a protective resistor and replace the ammeter with a milliammeter