topic 1 - energy

What are the 8 energy stores?

Kinetic, thermal (internal), chemical, gravitational potential, elastic potential, magnetic, electrostatic and nuclear.

What is a system in physics?

An object or group of objects being studied.

What is a closed system?

A system where no matter enters or leaves; energy may still be transferred between stores within it.

What is the principle of conservation of energy?

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

What are the 4 main pathways by which energy is transferred?

Mechanically, electrically, by heating and by radiation.

What is a mechanical energy transfer?

Energy is transferred when a force does work on an object.

What is an electrical energy transfer?

Energy is transferred when charge flows through a potential difference.

What is energy dissipation?

Energy spreads into the surroundings, usually as thermal energy, making it less useful.

What is a wasted energy transfer?

An energy transfer that is not useful for the intended purpose.

What is meant by a useful energy transfer?

An energy transfer that achieves the intended purpose of a device.

What happens to energy when a ball falls?

Gravitational potential energy decreases and kinetic energy increases; some energy may be dissipated by air resistance.

What happens to energy when a moving object slows down due to friction?

Kinetic energy is transferred to thermal energy in the object and surroundings.

What is the equation for kinetic energy?

Ek = 1/2 × m × v².

What does each symbol mean in Ek = 1/2mv²?

Ek = kinetic energy in joules (J), m = mass in kilograms (kg), v = speed in metres per second (m/s).

How do you calculate kinetic energy?

Multiply half the mass by the speed squared: Ek = 1/2mv².

What is the equation for gravitational potential energy?

Ep = m × g × h.

What does each symbol mean in Ep = mgh?

Ep = gravitational potential energy in joules (J), m = mass in kilograms (kg), g = gravitational field strength in N/kg, h = height in metres (m).

What is the approximate gravitational field strength on Earth?

9.8 N/kg, often rounded to 10 N/kg when instructed.

How can gravitational potential energy be increased?

Increase the object's mass or increase its height.

What is the equation for elastic potential energy?

Ee = 1/2 × k × e².

What does each symbol mean in Ee = 1/2ke²?

Ee = elastic potential energy in joules (J), k = spring constant in N/m, e = extension in metres (m).

What is the equation for work done?

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

What is the unit of work done?

The joule (J).

What does one joule of work mean?

One joule of work is done when a force of one newton moves an object one metre in the direction of the force.

What is power?

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

What is the equation for power?

P = E/t or P = W/t.

What do the symbols mean in P = E/t?

P = power in watts (W), E = energy transferred in joules (J), t = time in seconds (s).

What is one watt?

One watt is one joule of energy transferred per second.

How can you calculate energy transferred using power?

E = P × t.

What is the equation for efficiency using energy?

Efficiency = useful energy transferred ÷ total energy supplied.

How do you calculate efficiency as a percentage?

Efficiency (%) = (useful energy transferred ÷ total energy supplied) × 100.

How can efficiency be calculated using power?

Efficiency = useful power output ÷ total power input; multiply by 100 for a percentage.

Can efficiency be greater than 100%?

No. Energy is conserved, so useful output cannot exceed total input.

How can the efficiency of a device be improved?

Reduce unwanted energy transfers, for example by lubrication to reduce friction or insulation to reduce heating.

What is thermal insulation?

A material or method that reduces the rate of energy transfer by heating.

How does lubrication reduce energy dissipation?

It reduces friction between moving parts, so less energy is transferred to thermal energy.

How does thermal insulation reduce energy transfer?

It reduces the rate at which thermal energy moves to the surroundings.

What is the equation for energy transferred by heating?

ΔE = m × c × Δθ.

What does each symbol mean in ΔE = mcΔθ?

ΔE = change in thermal energy in joules (J), m = mass in kilograms (kg), c = specific heat capacity in J/kg°C, Δθ = temperature change in °C.

What is specific heat capacity?

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

What factors affect the energy needed to heat a substance?

The mass, the specific heat capacity and the temperature change.

How do you calculate temperature change?

Temperature change = final temperature − initial temperature.

How do you calculate specific heat capacity?

c = ΔE ÷ (m × Δθ).

What is the required practical for specific heat capacity?

Measure the mass of a metal block, insert a heater and thermometer, insulate the block, record the initial temperature, heat for a measured time and record the final temperature.

How can electrical energy supplied in the specific heat capacity practical be calculated?

E = V × I × t, where V is potential difference, I is current and t is time.

Why is insulation used in the specific heat capacity practical?

To reduce energy transfer to the surroundings so the result is more accurate.

How can the specific heat capacity practical be made more reliable?

Repeat measurements, use insulation, ensure good thermal contact between the heater and block, and measure mass and temperature carefully.

What is a renewable energy resource?

An energy resource that is replenished naturally as it is used.

What is a non-renewable energy resource?

An energy resource that is not replenished as quickly as it is used and will eventually run out.

Give examples of fossil fuels.

Coal, oil and natural gas.

Give examples of renewable energy resources.

Wind, solar, hydroelectricity, tidal, wave, geothermal and biofuel.

What is a fossil fuel?

A fuel formed over millions of years from the remains of ancient organisms.

How is electricity generated using fossil fuels?

Fuel is burned to heat water; steam turns a turbine, which drives a generator.

What are the advantages of fossil fuels?

They can generate electricity reliably when needed and are relatively easy to control.

What are the disadvantages of fossil fuels?

They are finite and burning them releases carbon dioxide; other pollutants may also be produced.

How does a nuclear power station generate electricity?

Nuclear fission releases energy that heats water; steam turns a turbine connected to a generator.

What are the advantages of nuclear power?

It produces large amounts of reliable electricity and very low carbon dioxide emissions during operation.

What are the disadvantages of nuclear power?

Radioactive waste must be stored safely, stations are expensive to build and decommission, and accidents can have serious consequences.

How does a wind turbine generate electricity?

Wind turns the turbine blades, which drive a generator.

What are the advantages of wind power?

It is renewable and produces no greenhouse gases during operation.

What are the disadvantages of wind power?

Output depends on wind speed; turbines can be noisy and affect the landscape.

How does solar power generate electricity?

Solar cells convert light energy directly into electrical energy.

What are the advantages of solar power?

It is renewable and produces no greenhouse gases during operation.

What are the disadvantages of solar power?

Output depends on sunlight and is lower at night or in cloudy conditions; installation can be expensive.

How does hydroelectric power generate electricity?

Water stored at height flows down and turns turbines connected to generators.

What are the advantages of hydroelectric power?

It is renewable, reliable when water is available and can respond quickly to changes in demand.

What are the disadvantages of hydroelectric power?

Dams are expensive to build and can flood habitats and settlements.

How does tidal power generate electricity?

Moving tidal water turns turbines or is used with a tidal barrage to generate electricity.

What are the advantages of tidal power?

Tides are predictable and renewable.

What are the disadvantages of tidal power?

Suitable sites are limited, construction is expensive and local habitats may be affected.

How does wave power generate electricity?

The movement of waves drives devices that generate electricity.

What are the advantages of wave power?

It is renewable and produces no greenhouse gases during operation.

What are the disadvantages of wave power?

Wave conditions vary, equipment can be damaged by storms and suitable locations are limited.

How does geothermal energy generate electricity?

Heat from underground warms water, producing steam to drive a turbine.

What are the advantages of geothermal energy?

It is renewable and can provide a steady energy supply in suitable locations.

What are the disadvantages of geothermal energy?

Suitable sites are limited and drilling and construction can be expensive.

What is a biofuel?

A fuel made from recently living biological material.

What are the advantages of biofuels?

They are renewable if crops or biomass are replaced sustainably and can use existing fuel technologies.

What are the disadvantages of biofuels?

Growing fuel crops can use land needed for food or habitats, and burning them releases carbon dioxide and pollutants.

Why must electricity generation use a mix of energy resources?

Demand changes, renewable output can be variable, and different resources have different costs, environmental impacts and reliability.

What is meant by a reliable energy resource?

One that can provide energy when it is needed.

What is meant by an intermittent energy resource?

One whose output varies with conditions, such as wind speed or sunlight.

What environmental effects can energy resources have?

They may release greenhouse gases or pollutants, use land, damage habitats, create waste or affect local communities.

What is the difference between energy and power?

Energy is the amount transferred, measured in joules; power is the rate of energy transfer, measured in watts.

How do you rearrange P = E/t to calculate time?

t = E ÷ P.

How do you rearrange Ek = 1/2mv² to calculate speed?

v = √(2Ek ÷ m).

How do you rearrange Ep = mgh to calculate height?

h = Ep ÷ (m × g).

How do you rearrange W = Fs to calculate force?

F = W ÷ s.

How do you rearrange W = Fs to calculate distance?

s = W ÷ F.

How do you calculate the total energy supplied if 600 J is transferred usefully and efficiency is 75%?

Total energy = useful energy ÷ efficiency as a decimal = 600 ÷ 0.75 = 800 J.

Why are energy resources compared using cost, reliability and environmental impact?

No resource is best in every situation, so decisions involve trade-offs between these factors.

What is meant by the payback time of an energy-saving measure?

The time taken for the money saved to equal the initial cost of the measure.

How do you calculate payback time?

Payback time = initial cost ÷ money saved per year.

Why might a house use loft insulation or double glazing?

To reduce the rate of energy transfer by heating, reducing energy use and bills.

What factors affect the choice of an energy-saving measure?

Initial cost, expected savings, payback time, lifespan and how much energy transfer it reduces.