Physics Chapter 1 Energy Transfers

Question 1

What is a system?

Answer 1

A system is an object or group of objects.

Question 2

What is a closed system?

Answer 2

A system where energy cannot enter or leave.

Question 3

In terms of energy, what happens when a system changes?

Answer 3

Energy must transfer from one store to another along an energy pathway.

Question 4

What are the units of energy? (Units and Symbol)

Answer 4

Joules (J)

Question 5

State the 8 energy stores

Answer 5

Gravitational Potential Energy (GPE)

Kinetic Energy (KE)

Elastic Potential Energy

Thermal (Internal)

Chemical

Magnetic

Electrostatic

Nuclear

Question 6

Describe how the gravitational potential energy store can increase or decrease.

Answer 6

Increase - Object raised higher above ground (higher in gravitational field)
Decrease - Object lowered (closer to centre of gravitational field)

Question 7

Describe how the kinetic energy store can increase or decrease.

Answer 7

Increase - Object speeds up (or becomes heavier)
Decrease - Object slows down (or becomes lighter)

Question 8

Describe how the elastic potential energy store can increase or decrease.

Answer 8

Increase - An object is stretched or squashed (deformed) in such a way that it would return to its original shape if the force was removed.
Decrease - The size of the deformation is reduced, so the object is closer to its original shape.

Question 9

Describe how the thermal (internal) energy store can increase or decrease.

Answer 9

Increase - Increase in temperature or a change of state (solid→liquid→gas)
Decrease - Decrease in temperature or a change in state (gas→liquid→solid)

Question 10

Describe how the chemical energy store can change.

Answer 10

Through chemical reactions.

Question 11

Describe how the magnetic energy store can change.

Answer 11

Changes to the strength, or location within a magnetic field.

Question 12

Describe how the electrostatic energy store can change.

Answer 12

Transfer of charges or changes to an electric field.

Question 13

Describe how the nuclear energy store can change.

Answer 13

Changes in the nucleus of atoms.

Question 14

Give an example of a chemical energy store.

Answer 14

Fuel

Food

Batteries

Question 15

State the principle of conservation of energy.

Answer 15

Energy cannot be created or destroyed, only transferred from one store to another along an energy pathway.

Question 16

Name the four energy pathways.

Answer 16

Mechanical (Forces)

Radiation (Waves)

Electrical

Heating

Question 17

What is work done.

Answer 17

A measure of energy transferred.

Question 18

State the equation that links work done, force, and distance in words and symbols.

Answer 18

Work done = Force x Distance
W=Fd
(Could also use W=Fs, where s is displacement)

Question 19

State the units of work done.

Answer 19

Joules (J)

Question 20

Rearrange the formula for work done to make Force, and then Distance the subject of the equation.

Answer 20

F=Wd
d=WF

Question 21

What is meant by useful energy?

Answer 21

Energy that is transferred to the store, or along the pathway, that is its intended function.

Question 22

What is meant by wasted energy?

Answer 22

Energy that is transferred to a store, or along a pathway, that does not support the action. This is usually the thermal store of the surroundings.

Question 23

What is dissipated energy?

Answer 23

Wasted energy that spreads out into (the thermal store of) the surroundings.

Question 24

State the formula for efficiency of a device in terms of both energy and power.

Answer 24

Efficiency = Useful energy outputTotal energy input(100%)
Efficiency = Useful power outputTotal power input(100%)

Question 25

Give some examples of how to reduce unwanted energy transfers.

Answer 25

Thermal insulation Lubrication Design for less energy lost through noise or heat

Question 26

Define Power

Answer 26

Power is energy transferred (work done) per second. Or Power is rate of energy transfer.

Question 27

State the equation linking Power, Energy and Time in both words and units

Answer 27

Power = EnergyTime P=Et

Question 28

State the units of Power

Answer 28

Watts (W)

Question 29

What does 1 Watt mean?

Answer 29

An energy transfer of 1 Joule per second.

Question 30

Compare the power of two electric motors that both lift the same weight through the same height, but one does it faster than the other.

Answer 30

The one which does it faster has the greater power.

Question 31

Describe how energy can be transferred by conduction.

Answer 31

Vibrations (kinetic energy) in particles pass energy on to neighbouring particles through collisions.

Question 32

What does high thermal conductivity mean?

Answer 32

There is a high rate of energy transfer by conduction across the material.

Question 33

What sort of materials make good thermal conductors and why?

Answer 33

Metals - lots of delocalised electrons to pass on collisions Solids - particles are packed close together

Question 34

What sort of materials make good thermal insulators and why?

Answer 34

Wood, plastics, ceramics - electrons are tightly bound within chemical bonds Gases - particles are spread out Vacuums - Conduction cannot occur in a vacuum

Question 35

Describe how energy can be transferred by convection.

Answer 35

Increased vibrations (kinetic energy) in hot particles of a liquid or gas cause particles to spread out, decreasing their density and making them ‘float’ on colder fluid. a.k.a. ‘Heat rises’

Question 36

What is meant by a fluid?

Answer 36

A liquid or a gas

Question 37

Describe how energy can be transferred by radiation.

Answer 37

Energy is transferred as waves emitted by all objects.

Question 38

Which of the three heating energy transfers can occur in a vacuum?

Answer 38

Radiation - As it does not require particles.

Question 39

Which of the three heating energy transfers cannot occur in solids?

Answer 39

Convection - As particles need to be able to move (flow).

Question 40

What factors affect the rate of cooling of a building?

Answer 40

The thickness and thermal conductivity of its walls. Levels of insulation Double glazing Opening/closing doors and windows

Question 41

In the insulation required practical, what is the independent variable?

Answer 41

Either: Thickness of insulating material (continuous) Number of layers of insulating material (discrete) Type of insulating material (categoric)

Question 42

In the insulation required practical, what is the dependent variable?

Answer 42

Rate of cooling, or, rate of thermal transfer.

Question 43

State what variables must be controlled?

Answer 43

Mass or volume of water Starting temperature of water Temperature of surroundings Shape of container