P1 - Energy

What is a system in physics?

An object or group of objects being studied.

What are the eight energy stores?

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

What is the kinetic energy store?

The energy store of a moving object.

What is the thermal energy store?

The energy store associated with the temperature of an object.

What is the gravitational potential energy store?

Energy stored when objects are separated by a gravitational field.

What is the elastic potential energy store?

Energy stored when an object is stretched or compressed.

What is the chemical energy store?

Energy stored in chemical substances, such as fuels and food.

What is the magnetic energy store?

Energy stored due to the positions of interacting magnets.

What is the electrostatic energy store?

Energy stored due to the positions of charged objects.

What is the nuclear energy store?

Energy stored in atomic nuclei.

What are the four main pathways of energy transfer?

Mechanically, electrically, by heating and by radiation.

What is meant by energy transferred mechanically?

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

What happens to energy when an object is projected upwards?

Its kinetic store decreases and its gravitational potential store increases.

What happens when a moving object hits an obstacle?

Kinetic energy is transferred to other stores, including thermal and sound stores.

What happens to energy when a vehicle slows down?

The vehicle's kinetic energy decreases; energy is dissipated mainly to thermal stores of the brakes, tyres, road and surroundings.

What is the equation for kinetic energy?

Ek = 0.5 x m x v^2

What do the symbols in Ek = 0.5 x m x v^2 mean?

Ek = kinetic energy (J); m = mass (kg); v = speed (m/s).

What is the equation for elastic potential energy?

Ee = 0.5 x k x e^2

What do the symbols in Ee = 0.5 x k x e^2 mean?

Ee = elastic potential energy (J); k = spring constant (N/m); e = extension (m).

When can you use the elastic potential energy equation?

When the spring's limit of proportionality has not been exceeded.

What is the equation for gravitational potential energy gained?

Ep = m x g x h

What do the symbols in Ep = m x g x h mean?

Ep = gravitational potential energy (J); m = mass (kg); g = gravitational field strength (N/kg); h = height (m).

What happens to kinetic energy if speed doubles?

It becomes four times greater if mass stays constant.

What happens to kinetic energy if mass doubles?

It doubles if speed stays constant.

What happens to gravitational potential energy if height doubles?

It doubles if mass and gravitational field strength stay constant.

What is the equation for change in thermal energy?

Delta E = m x c x Delta theta

What does specific heat capacity mean?

The energy needed to raise 1 kg of a substance by 1 degree Celsius.

What are the units of specific heat capacity?

J/kg degrees Celsius.

What do the symbols in Delta E = m x c x Delta theta mean?

Delta E = energy change (J); m = mass (kg); c = specific heat capacity; Delta theta = temperature change (degrees Celsius).

How do you calculate temperature change?

Final temperature minus initial temperature.

What is power?

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

What is the equation linking power, energy and time?

P = E / t

What is the equation linking power, work done and time?

P = W / t

What are the units of power, energy and time?

Power: watts (W); energy or work: joules (J); time: seconds (s).

What does 1 watt mean?

One joule of energy transferred per second.

How can two motors have different powers if they lift the same load?

The more powerful motor transfers energy and does the same work in less time.

How do you calculate energy transferred using power and time?

E = P x t

What is the law of conservation of energy?

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

What happens to total energy in a closed system?

The total energy remains constant, although energy may transfer between stores.

What is meant by a useful energy transfer?

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

What is meant by dissipated energy?

Energy transferred to less useful stores, usually the thermal stores of the surroundings.

Why is dissipated energy often called wasted energy?

It spreads into the surroundings and becomes less useful for the intended purpose.

What is the equation for efficiency using energy?

Efficiency = useful energy output / total energy input

What is the equation for efficiency using power?

Efficiency = useful power output / total power input

How do you convert efficiency from a decimal to a percentage?

Multiply the decimal efficiency by 100.

Can efficiency be greater than 100%?

No. Useful output cannot exceed total input.

A device transfers 80 J usefully from 200 J input. What is its efficiency?

80 / 200 = 0.4 = 40%.

Why is no real energy transfer device perfectly efficient?

Some energy is inevitably dissipated into less useful stores.

How can lubrication improve efficiency?

It reduces friction, decreasing unwanted heating and energy dissipation.

How can thermal insulation improve efficiency?

It reduces unwanted energy transfer by heating to the surroundings.

How does increasing wall thickness affect a building's cooling rate?

Thicker walls generally reduce the rate of energy transfer, so the building cools more slowly.

How does higher thermal conductivity affect cooling?

Higher thermal conductivity increases the rate of energy transfer by conduction through a material.

What is the aim of the specific heat capacity required practical?

To determine the specific heat capacity of one or more materials.

What equipment is needed for the specific heat capacity practical?

A material block, heater, thermometer, balance, joulemeter or suitable electrical meters, power supply and insulation.

How do you calculate the mass of a block?

Measure it using a balance and record the mass in kilograms.

How is energy supplied to the block measured?

Use a joulemeter, or calculate energy supplied using electrical power multiplied by heating time.

How do you calculate specific heat capacity from practical results?

c = energy supplied / (mass x temperature change).

Why is the block insulated during the practical?

To reduce energy transfer to the surroundings.

Why is the heater placed in a hole in the block?

To transfer energy directly to the block.

Why should the thermometer be placed securely in the block?

To measure the block's temperature accurately.

How can the specific heat capacity experiment be improved?

Use insulation, ensure good contact between heater and block, stir if appropriate for a liquid, and repeat measurements.

Why might the measured specific heat capacity be inaccurate?

Some supplied energy heats the surroundings rather than the material.

What is the independent variable in a comparison of different block materials?

The material being tested.

What should be controlled when comparing different materials?

Mass, starting temperature, energy supplied and experimental conditions.

What is a renewable energy resource?

A resource that is replenished as it is used.

What is a non-renewable energy resource?

A resource that is not replenished quickly enough to replace what is used.

Which energy resources are fossil fuels?

Coal, oil and natural gas.

Is nuclear fuel renewable?

No. The fuel supply is finite.

Is biofuel renewable?

Generally yes, if it is replenished sustainably.

Which resources are renewable?

Wind, hydroelectricity, geothermal, tidal, solar, water waves and sustainably replenished biofuels.

What are the three main uses of energy resources?

Transport, electricity generation and heating.

Why are fossil fuels useful?

They are reliable, can provide energy on demand and have established infrastructure.

What are the disadvantages of fossil fuels?

They release carbon dioxide when burned; extraction and pollution can damage environments.

What are the advantages of nuclear energy?

It produces large amounts of electricity reliably and has very low operational carbon dioxide emissions.

What are the disadvantages of nuclear energy?

Radioactive waste needs safe management; plants are expensive to build and decommission.

What are the advantages of wind and solar energy?

They are renewable and generate electricity without direct greenhouse gas emissions during operation.

What are the disadvantages of wind and solar energy?

Output depends on weather and conditions; storage or backup may be needed.

What are the advantages of hydroelectric power?

It is renewable, can respond quickly to demand and can be reliable where water is available.

What are the disadvantages of hydroelectric power?

Dams can flood habitats and settlements and disrupt ecosystems.

What are the advantages of tidal and wave energy?

They are renewable; tidal patterns are predictable, although output varies.

What are the disadvantages of tidal and wave energy?

They can be expensive, affect marine environments and are limited to suitable locations.

What are the advantages of geothermal energy?

It is renewable where heat is replenished and can provide a reliable supply in suitable locations.

What are the disadvantages of geothermal energy?

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

What are the advantages of biofuels?

They can be replenished and may use plant material or waste.

What are the disadvantages of biofuels?

Growing crops can compete with food production and land for habitats; burning them releases carbon dioxide.

What makes an energy resource reliable?

Its ability to provide energy when needed, including how dependent it is on weather or other conditions.

Why are fossil fuels and nuclear energy generally reliable?

They can provide controllable energy output when fuel and functioning facilities are available.

Why are wind and solar less reliable for continuous supply?

Their output depends on wind speed or sunlight.

Why might a country use a mixture of energy resources?

To balance reliability, cost, availability, environmental impacts and energy demand.

Why might energy-resource use change over time?

Technology, prices, demand, resource availability, government policy and environmental concerns change.

Why might governments struggle to act on environmental issues?

Decisions involve economic costs, political priorities, social needs and ethical considerations.