CP3 - Conservation of energy

Unit of energy

Joule (j)

What are the energy stores?

Chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic and nuclear

How is energy transferred?

Mechanically, electrically, by heating, by radiation (sound and light)

Principle of conservation of energy

Energy is not created or destroyed

In an energy transfer diagram, how do you represent energy transfers?

By writing the name of the energy store and its location in a box.

What happens to wasted energy in energy transfers?

It is transferred to the thermal energy store of the surroundings, then spread out and dissipated.

In an energy transfer diagram how do you represent energy transfers?

By writing the name of the energy transfer above an arrow between two energy stores.

Give the equation linking efficiency, useful energy output and total energy input.

Efficiency = (useful energy output/total energy input) x100%

What do the widths of the arrows represent on a Sankey diagram?

The amount of energy

Why do mechanical processes waste energy?

There is always friction between the moving parts that causes them to heat up and transfer energy to the surroundings that is then dissipated.

How can you reduce energy wastage in mechanical transfers?

Lubricate the parts (e.g with oil) to reduce friction

Efficiency

How good a machine is at transferring energy into useful forms

How can you increase the efficiency of a machine?

By reducing energy losses - for example reducing friction or ensuring that all fuel going into an engine is burnt.

Which way is thermal energy transferred?

From a hotter place to a colder place

Heat conduction

The transfer of thermal energy through a substance without the substance itself moving

Convection

The transfer of thermal energy through the upward movement of less dense, warmer fluid.

Thermal radiation

The transfer of energy by infra-red waves

Why do metals conduct heat better than insulators?

Metals have free electrons that can pass along energy.

Why does air become less dense when you heat it?

The particles move further apart

Why does hot air rise?

It is less dense than cold air so it floats.

What type of surface is the best reflector of heat?

A shiny white surface

What type of surface is the best absorber of heat?

A matt black surface

What type of surface is the best radiator of heat?

A matt black surface

What type of surface is the worst radiator of heat?

A shiny white surface

How is the use of renewable energy sources changing?

The use of renewable energy is increasing

Two disadvantages of solar energy

Doesn’t work well without a sunny climate and long days

Two disadvantages of using wind energy

Can kill birds and needs a windy location.

Two disadvantages of using tidal power

Need a location with large tidal range, the dam might affect wildlife

Two disadvantages of hydroelectric power

The reservoir may destroy the natural habitat of wildlife, can displace people whom had their homes where the reservoir is.

Disadvantages of wave energy

Wildlife might be affected

Disadvantage of using geothermal energy

Need a location with hot rocks close to the surface of the Earth.

How do most types of insulation keep homes warm?

Air is trapped which stops convection currents circulations and reduces conduction

How to reduce energy transfer by radiation?

By using shiny surfaces to reflect infrared radiation back

Thermal conductivity

How easily energy is transferred through a substance by heating.

Two factors that affect the rate that thermal energy is transferred through an object

Thickness of the object

Thermal conductivity of the object

Three factors affecting GPE

Mass, height, gravitational field strength

GPE equation

GPE = mass x height x gravitational field strength

Two factors affecting KE and which one has the biggest effect?

Mass and velocity. Velocity has biggest effect.

KE equation

KE = 0.5 x mass x velocity squared

Relationship between GPE and KE for a falling object

GPE is transferred to KE

What is meant by a non-renewable energy source?

It cannot be replaced once it has been used.

Name the three main non-renewable fuels

Coal, oil, natural gas

Advantages of non renewable fuels

Easy to transport, cheap, high energy density

Disadvantages of fossil fuels

Pollution - carbon dioxide contributes to climate change and sulphur dioxide that causes acid rain.

Disadvantages of nuclear fuels

Radioactive waste is expensive to dispose of and even then can’t be properly disposed. Nuclear plans are expensive to decommission and very rare nuclear accidents have serious consequences.

Describe the current trends in non-renewable fuel usage

Most countries are trying to cut down on the use of fossil fuels. Some countries are moving away from nuclear while some are increasing their usage.

Name the 6 principle non-renewable energy sources in use today

Solar, tidal, wind, hydroelectric, wave, geothermal

How does solar energy work?

Solar cells convert the energy directly into an electrical transfer, or solar energy can be used to heat water.

How does tidal power work?

Water turns turbines across a dam in an estuary, or by using underwater turbines.

Why can’t we only use renewable energy sources?

Renewable energy is often intermittent, and so we need non-renewables to be consistent and fill the gaps.