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Physics > Energy > Flashcards

Energy Flashcards

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Physics 101 flashcards AP® Physics flashcards
1
Q

What is the law of conservation of energy?

A

Energy cannot be created nor destroyed, only transferred between energy stores, stored or dissipated

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2
Q

What are the energy stores?

A

Kinetic
Gravitational potential

Chemical
Elastic potential
Magnetic
Electrostatic
Nuclear
Thermal

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3
Q

How can energy be transferred?

A

.heating
.mechanically (work done by forces) like pulling a rubber band for elastic potential
.electrically (work done by moving charges) like plugging something into a socket

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4
Q

What is a system?

A

An object or group of objects

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5
Q

What happens when a system changes?

A

Energy is transferred

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6
Q

What is a closed system?

A

Where neither mass nor energy can enter or leave. The net change in the total energy is always zero.

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7
Q

Describe the changes in stores and how it’s transferred when boiling a kettle.

A

Electrical energy from the plug socket transfers electrically to the thermal energy store.

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8
Q

What is work done?

A

Another way of saying energy transferred.

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9
Q

Describe the changes in stores and how it’s transferred when throwing a ball upwards.

A

Energy transfers from the chemical store of the person’s arm to the kinetic energy store of the ball and arm.

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10
Q

Describe the changes in stores and how it’s transferred when a moving object hits an obstacle.

A

Energy transfers from the moving object’s kinetic energy store to other energy stores e.g elastic potential and thermal energy of stationary and moving object.

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11
Q

Describe the changes in stores and how it’s transferred when a car brakes.

A

Energy transfer’s from the wheel’s kinetic energy to the thermal energy of the surroundings

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12
Q

Describe the changes in stores and how it’s transferred when a ball is dropped and accelerated by gravity.

A

Energy is transferred from the ball’s gravitational potential store to it’s kinetic.

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13
Q

Define kinetic energy

A

The store that all moving matter has.

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14
Q

What is kinetic energy directly proportional to?

A

The object’s mass and to the square of it’s velocity.

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15
Q

What is the equation for kinetic energy store?

A

Ek =1/2 mv^2

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16
Q

What does the ‘m’ symbol mean? What’s it’s units?

A

mass
Kg

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17
Q

What does the ‘v’ symbol mean?

A

velocity (speed)

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18
Q

What is speed’s units?

A

m/s

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19
Q

Define gravitational potential.

A

The store of energy that all raised matter has.

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20
Q

What is gravitational potential energy directly proportional to?

A

Mass of the object and the distance hat it is risen.

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21
Q

What is the equation for gravitational potential energy store?

A

Ep =mgh

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22
Q

What does the symbol ‘g’ stand for? What are it’s units?

A

Gravitational field strength (N/Kg)

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23
Q

What is ‘h’? What are it’s units?

A

height
m

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24
Q

What is energy measured in?

A

Joules

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25
Q

Define elastic potential energy store.

A

The store of energy that stretched or compressed objects experience.

26
Q

What is the equation for elastic potential energy store?

A

E =1/2ke^2
e

27
Q

What is ‘e’ in elastic potential energy equation? What are it’s units?

A

extension (m)

28
Q

What is the ‘k’ in elastic potential energy equations? What are it’s units?

A

spring constant (N/m)

29
Q

What is specific heat capacity?

A

The amount of energy required to raise the temperature of 1kg of a substance by 1 degrees.

29
Q

What is the equation for specific heat capacity?

A

change in energy= mass x specific heat capacity x change in temperture

30
Q

How do you investigate specific heat capacity?

A

1) need a block of the material with two holes ( for heater and thermometer)
2) measure mass of block then wrap in insulating layer
3) Insert heater and thermometer. Measure initial temperature
4)Set potential difference to 10V
5) As block heats up (from current doing work on heater) take readings every minute for 10 minutes
6) Use P=VT to calculate power then use E=Pt to work out energy transferred
7) Do a line graph of energy transferred and temperature and find the gradient
8) 1/(gradient x mass of block)

31
Q

Give the two equations for power

A

P=W/t
P=E/t

32
Q

True or false:
A substance with high specific heat requires minimal energy to raise temperature

A

False

33
Q

True or false:
Substances with high specific heat capacity take a long to cool down

A

True

34
Q

True or false:
Some devices are 100 percent efficient

A

No device is 100 percent efficient

35
Q

Explain how energy is transferred and dissipated in a phone.

A

A phone is a system. When you use the phone, energy is transferred form the chemical energy of the battery. Some of this energy is dissipated to the thermal energy store if the phone.

36
Q

What is another name of dissipated energy?

A

Waste energy

37
Q

Describe energy transfers for closed systems using an example

A

A cold spoon is dropped into an insulated flask of hot soup, which is then sealed. Assuming the flask is a perfect insulator, the spoon and soup form a closed system. Energy is transferred from the thermal energy store of the soup to the useless thermal energy store of the spoon. Energy transfers have occurred within the system but no energy has left so the net change in energy is zero.

38
Q

What is power?

A

Rate of doing work

39
Q

What are the two equations for efficiency?

A

efficiency= useful output energy transfer/ total input energy transfer

efficiency= useful power output/ total power input

40
Q

What can convection happen in?

A

liquids
gasses

41
Q

Explain conduction

A

Particles in the part of the object being heated vibrate more and collide with each other. These collisions cause energy to be transferred between particle’s kinetic energy stores.

42
Q

Explain a convection current using radiators as an example

A

1) Energy is transferred from the radiator to the nearby particles by conduction
2) The air particles around collide with radiator surface and becomes warmer and less dense as the particles move quicker
3) The warm air rises and is replaced by cooler air. This cool air gets heated by the radiator
4) At the same time, the previously heated air transfers energy to surrounding, it cools, becomes denser and sinks
5) This cycle repeats causing air flow to circulate round the room

43
Q

Explain how lubrication reduces unwanted energy transfers

A

Whenever something moves, there’s usually a frictional force acting against it which causes some energy in the system to be dissipated. Lubricants e.g. oil reduce the friction.

44
Q

Give examples of thermal insulation and whether they reduce energy transfers by convection or conduction

A

1) cavity walls- have an air gap which reduces amount of energy transfer by conduction
2) double glazed windows- reduce energy transfer by conduction

1) cavity wall insulators- filled with foam reducing energy transfer by convection
2) draught excluders- around doors and windows reduce energy transfer by convection

45
Q

How can you investigate the effectiveness of material as thermal insulators?

A

1) Boil water in a kettle. Pour some water into a sealable container
2) Measure the mass of water in container
3) Use thermometer to measure initial temperature of water
4) Seal container for another 5 minutes (stopwatch) then measure final temperature
5)Pour away water and allow container to cool to room temperature
6) Repeat the experiment but wrap the container in a different material. Make sure mass of water is the same

46
Q

How do thicker walls affect it’s thermal conductivity?

A

The thicker the walls, the lower the thermal conductivity

47
Q

What are the 3 non- renewable energy resources?

A

.coal
.oil
.(natural) gas

48
Q

State the pros and cons of fossil fuels

A

Pros:
.readily available (at the moment)
.relatively easy to produce energy from

Cons:
.non-renewable - will eventually run out
.release CO2 when burnt- greenhouse gas
.release sulphur dioxide when burnt- acid rain

49
Q

What is a renewable energy resource?

A

one that is being (or can be)
replenished as it is used

50
Q

What are the uses of energy resources?

A

.transport
.generation
.heating
.electricity

51
Q

What are the pros and cons of wind power?

A

Pros:
.no pollution after manufactured
.minimal running cost

Cons:
.wind turbines spoil the view
.loud
.unreliable- need constant wind
.high initial cost

52
Q

What are the pros and cons of solar cells?

A

Pros:
.no pollution after manufactured
.low running cost

Cons:
.unreliable- only reliable in sunny countries and only at daytime
.expensive to buy

53
Q

What is the problem with renewable energy resources?

A

Don’t generate as much electricity and non-renewable

54
Q

What are the pros and cons of geothermal power?

A

Pros:
.no emissions

Cons:
.limited locations that are suitable for power plants
.cost of building station

55
Q

How do geothermal power stations work?

A

Cold water is pumped down to hot rocks, produces steam that drives the turbine which generated electricity.

56
Q

What does hydroelectric power use?

A

falling water

57
Q

What are the prod and cons of hydroelectric power?

A

Pros:
.no pollution
.low running cost
.immediate response to increased electricity demand

Cons:
.not attractive
.high start up costs
.unreliable if drought
.disturb marine life

58
Q

What are he pros and cons of tidal barrages?

A

Pros:
.no pollution
.you can predict the tides
.minimal running cost

Cons:
.prevents boat access
.alters habitat of wildlife
.height of tide is variable

59
Q

What are bio fuels created from?

A

Plant products or dung that are burnt to produce electricity.

60
Q

What are the pros and cons of biofuels?

A

Pros:
.renewable
.carbon neutral

Cons:
.crops use land and water (forests clears- loss of natural habitat)
.

Physics (4 decks)

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