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Form 3 Science > Physics Chapter 1 Energy Transfers > Flashcards

Physics Chapter 1 Energy Transfers Flashcards

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1
Q

What is a system?

A

A system is an object or group of objects.

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2
Q

What is a closed system?

A

A system where energy cannot enter or leave.

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3
Q

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

A

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

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4
Q

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

A

Joules (J)

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5
Q

State the 8 energy stores

A

Gravitational Potential Energy (GPE)

Kinetic Energy (KE)

Elastic Potential Energy

Thermal (Internal)

Chemical

Magnetic

Electrostatic

Nuclear

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6
Q

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

A

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

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7
Q

Describe how the kinetic energy store can increase or decrease.

A

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

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8
Q

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

A

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.

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9
Q

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

A

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

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10
Q

Describe how the chemical energy store can change.

A

Through chemical reactions.

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11
Q

Describe how the magnetic energy store can change.

A

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

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12
Q

Describe how the electrostatic energy store can change.

A

Transfer of charges or changes to an electric field.

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13
Q

Describe how the nuclear energy store can change.

A

Changes in the nucleus of atoms.

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14
Q

Give an example of a chemical energy store.

A

Fuel

Food

Batteries

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15
Q

State the principle of conservation of energy.

A

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

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16
Q

Name the four energy pathways.

A

Mechanical (Forces)

Radiation (Waves)

Electrical

Heating

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17
Q

What is work done.

A

A measure of energy transferred.

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18
Q

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

A

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

19
Q

State the units of work done.

A

Joules (J)

20
Q

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

A

F=Wd
d=WF

21
Q

What is meant by useful energy?

A

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

22
Q

What is meant by wasted energy?

A

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.

23
Q

What is dissipated energy?

A

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

24
Q

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

A

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

25
Q

Give some examples of how to reduce unwanted energy transfers.

A

Thermal insulation

Lubrication

Design for less energy lost through noise or heat

26
Q

Define Power

A

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

27
Q

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

A

Power = EnergyTime
P=Et

28
Q

State the units of Power

A

Watts (W)

29
Q

What does 1 Watt mean?

A

An energy transfer of 1 Joule per second.

30
Q

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.

A

The one which does it faster has the greater power.

31
Q

Describe how energy can be transferred by conduction.

A

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

32
Q

What does high thermal conductivity mean?

A

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

33
Q

What sort of materials make good thermal conductors and why?

A

Metals - lots of delocalised electrons to pass on collisions

Solids - particles are packed close together

34
Q

What sort of materials make good thermal insulators and why?

A

Wood, plastics, ceramics - electrons are tightly bound within chemical bonds

Gases - particles are spread out

Vacuums - Conduction cannot occur in a vacuum

35
Q

Describe how energy can be transferred by convection.

A

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’

36
Q

What is meant by a fluid?

A

A liquid or a gas

37
Q

Describe how energy can be transferred by radiation.

A

Energy is transferred as waves emitted by all objects.

38
Q

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

A

Radiation - As it does not require particles.

39
Q

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

A

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

40
Q

What factors affect the rate of cooling of a building?

A

The thickness and thermal conductivity of its walls.

Levels of insulation

Double glazing

Opening/closing doors and windows

41
Q

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

A

Either:
Thickness of insulating material (continuous)

Number of layers of insulating material (discrete)

Type of insulating material (categoric)

42
Q

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

A

Rate of cooling, or, rate of thermal transfer.

43
Q

State what variables must be controlled?

A

Mass or volume of water

Starting temperature of water

Temperature of surroundings

Shape of container

Form 3 Science (4 decks)

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