Energy resources and transfers

Chemical potential store

Transferred by chemical reactions; e.g. chemical energy store of muscles

Kinetic energy store

Moving objects have kinetic energy e.g. vibrating ions in wire

Gravitational potential energy

Object moved through a gravitational field

Elastic potential energy

Stretched/squashed/bent object has elastic potential

Thermal energy store

Hotter = more thermal energy

Magnetic energy store

Magnetic materials interacting with each other have magnetic energy store

Electrostatic energy store

Charged particles (electrons, protons)

Nuclear energy store

Energy released nuclear store during nuclear reactions

When a force acts on an object, energy is transferred

Mechanically

Examples of mechanical energy transfer

Pull, push, stretch, squash

Electrical energy transfer

Transferred by charge moving through a potential difference (current)

Energy transferred by heating

Hotter to cooler object - Conduction, convection, radiation

Which objects don’t have energy in their thermal energy store

Objects at 0 degrees K

Energy transfer by radiation

Energy transferred by electromagnetic waves (light) or mechanical waves (sound)

Conservation of energy

Energy cannot be destroyed or created

Where will the total amount of energy within a system always be the same

In a closed system

Relationship between efficiency, useful energy output and total energy output

Efficiency = useful energy output/total energy output x100

How can thermal energy transfer take place

Conduction, convection, radiation

Which kind of thermal energy transfer can take place in a vacuum

Radiation

Which kind of thermal energy transfer requires particles to transfer energy

Conduction, convection

Which kind of thermal energy transfer cannot occur in solids

Convection

Which kind of thermal energy transfer takes place only in solids

Conduction

Why are metals good thermal conductors

Delocalised electrons move and collide with metal ions to transfer energy

Why are materials with trapped air good insulators

Air cannot move to form convection current → only conduction occurs → very slow as air is a gas

What happens to particles in a fluid as the fluid is heated

They move apart from each other - volume of fluid expands

What happens to particles of a fluid as a fluid is cooled

Particles move closer together and volume of fluid contracts

What kind of objects emit IR radiation

All objects above 0 kelvin

How does the temperature of an object affect the amount of thermal radiation given off

Hotter objects radiate more in a given time

Black objects are

Good absorbers and emitters of thermal radiation

Dull objects are

Reasonable absorbers and emitters of thermal radiaition

Shiny objects are

Very poor absorbers + emitters of thermal radiation

White objects are

Poor absorbers and emitters of thermal radiation

How is energy transferred by radiation from an object’s surface

Objects emit electromagnetic waves e.g. infrared or light which transfer energy

Dependent variable in investigating conduction

Time taken for ball bearing to drop to ground as wax melts

How to reduce unwanted energy transfer

Insulation

Investigate radiation practical dependent variable

Record temperature at regular intervals

How to improve radiation practical

Data logger connected to digital thermometer is more accurate

Why is convection current faster in a hotter fluid

Higher kinetic energy

Radiation practical control variables

Amount of wax used to plug top of flask, SA of flask, temp and vol of hot water at start

How does thermal conductivity affect the insulating ability of a material

Lower thermal conductivity = better insulator

How does density of a material affect a material’s insulating abilities

More dense = particles closer together = transfers energy more easily = worse insulator

How do you reduce convection

Prevent fluid which forms convection current from moving

How does thickness of a material affect insulating abilities

Thicker = better insulator

Relationship between work done, force and distance moved in direction of force

W = Fd

Work is done when

object is moved over a distance by force applied in direction of its displacement

Work done is measured in

Joules

Relationship between work done and energy transferred

Work done = energy transferred

Relationship between grav potential energy, mass, grav field strength, height

GPE = mgh

Relationship between kinetic energy, mass and speed

KE = ½ mv²

How does conservation of energy produce a link between GPE, KE and work

Work done transfers energy between GPE and KE stores

When a ball is lifted to a height what happens

Work done on ball; gains GPE; mechanical transfer to KE when drop

What is power

Rate of transfer of energy / rate of doing work

Relationship between power, work done and time taken

P = W/t

Relationship between power, energy transferred and time taken

P = E/t

Power is measured in

Watts