P6.1 Energy

What are the eight energy stores

Thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic and nuclear.

What are the four energy transfer pathways?

Mechanically, electrically, by heating and by radiation.

What is meant by a system in physics?

An object or group of objects under observation

State the principle of conservation of energy.

Energy cannot be created or destroyed; it can only be transferred between stores and dissipated

What is meant by a closed system?

A system in which no energy enters or leaves.

What is meant by energy being dissipated?

Energy transfers into the surroundings, usually into thermal stores

Why is dissipated energy described as wasted energy?

It is transferred to stores that are less useful for the intended purpose.

State the equation linking work done, force and distance.

Work done = force × distance moved in the direction of the force; W = Fs.

What is the unit of work done?

joules (J).

What is the equation for kinetic energy?

Ek = ½mv².

What is the equation for gravitational potential energy?

Ep = mgh.

State the equation linking weight, mass and gravitational field strength.

W = mg.

What is the equation for elastic potential energy?

Ee = ½ke².

What is the equation for energy transferred when heating a substance?

ΔE = mcΔθ.

Define specific heat capacity.

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

State the equation linking energy transferred, charge and potential difference.

E = QV.

State the equation linking power, energy transferred and time.

P = E/t.

State the equation linking power, work done and time.

P = W/t.

What is power?

The rate at which energy is transferred or work is done.

How can friction reduce the efficiency of a mechanical system?

Friction transfers energy to thermal stores of the surfaces and surroundings.

How can thermal energy losses from a house be reduced?

Use insulation to reduce the rate of energy transfer to the surroundings.

What is the purpose of lubrication in a machine?

To reduce friction and unwanted energy transfers.

What is the difference between renewable and non-renewable energy resources?

Renewable resources are replenished; non-renewable resources are not replenished and will eventually run out.

Name the main renewable energy resources in the AQA specification.

Biofuel, wind, hydroelectricity, geothermal, tidal, solar and wave power.

Give one advantage and one disadvantage of fossil fuels.

They provide reliable energy on demand, but burning them releases carbon dioxide and other pollutants.

Give one advantage and one disadvantage of nuclear power.

It produces reliable electricity with low operational carbon dioxide emissions, but produces radioactive waste and uses finite fuel.

Give one advantage and one disadvantage of wind power.

It is renewable and produces no emissions during operation, but electricity generation depends on wind conditions.

Give one advantage and one disadvantage of solar power.

It is renewable and produces no emissions during operation, but output depends on sunlight.

Give one advantage and one disadvantage of biofuels.

They are renewable if crops are replanted, but growing crops uses land and burning biofuel releases carbon dioxide.

Give one advantage and one disadvantage of hydroelectric power.

It is renewable and can respond to demand, but reservoirs can flood habitats and communities.

Give one advantage and one disadvantage of tidal power.

Tides are predictable and renewable, but suitable sites are limited and construction can affect habitats.

Give one advantage and one disadvantage of geothermal power.

It is renewable in suitable locations, but useful sites are geographically limited.

Why does the UK use a mixture of energy resources?

To meet changing demand while balancing reliability, cost, availability and environmental impact.

Application: A 20 N force moves a box 3 m in the direction of the force. Calculate the work done.

W = Fs = 20 × 3 = 60 J.

Application: A 2 kg object moves at 4 m/s. Calculate its kinetic energy.

Ek = ½ × 2 × 4² = 16 J.

Application: A 5 kg object is raised 2 m. Take g = 10 N/kg. Calculate its gain in GPE.

Ep = mgh = 5 × 10 × 2 = 100 J.

Application: A 2 kg object has a weight of 16 N on another planet. Calculate the gravitational field strength.

g = W/m = 16/2 = 8 N/kg.

Application: A 0.5 kg metal block is heated by 2,000 J and its temperature rises by 10°C. Calculate its specific heat capacity.

c = ΔE/(mΔθ) = 2000/(0.5 × 10) = 400 J/kg°C.

Application: A heater transfers 12,000 J in 60 s. Calculate its power.

P = E/t = 12,000/60 = 200 W.

Application: A device transfers 360 J of energy to 30 C of charge. Calculate the potential difference.

V = E/Q = 360/30 = 12 V.

Application: A spring with spring constant 200 N/m is extended by 0.10 m. Calculate its elastic potential energy.

Ee = ½ke² = ½ × 200 × 0.10² = 1 J.

Application: A moving object slows down because of friction. Explain what happens to its energy.

Its kinetic energy store decreases; energy is transferred mainly to thermal stores of the surfaces and surroundings.

Application: A student says energy has been lost because a bouncing ball eventually stops. Explain why this is incorrect.

Energy has not been destroyed; it has been transferred to thermal stores and sound in the ball, floor and surroundings.

Application: A student says energy has been lost because a bouncing ball eventually stops. Explain why this is incorrect.

Energy has not been destroyed; it has been transferred to thermal stores and sound in the ball, floor and surroundings.

Application: Two kettles heat the same mass of water through the same temperature rise. One requires more energy. Compare their