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Y11 PHYSICS > ENERGY RESOURCES AND ENERGY TRANSFERS > Flashcards

ENERGY RESOURCES AND ENERGY TRANSFERS Flashcards

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AP® Physics flashcards Physics 101 flashcards
1
Q

What is energy?

A

-Energy is a fundamental property of the Universe

  • It is measured in JOULES (J)
  • It exists everywhere and cannot be created or destroyed – The Principle of the Conservation of Energy
  • We cannot always see energy, but we see its effects
  • Energy has the ability to make things happen (do work)
  • Energy can be STORED or TRANSFERRED
  • Energy is just energy – but we think of it as existing as different ENERGY STORES and transferred through ENERGY PATHWAYS
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2
Q

Energy stores?

A
  • Gravitational potential
  • Elastic potential
  • Electrostatic
  • Chemical
  • Nuclear
  • Thermal
  • Magnetic
  • Kinetic
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3
Q

Energy pathways?

A
  • By heating (conduction & convection)
  • By radiation (e.g, EM radiation like light, infrared ect)
  • Mechanically
  • Chemically
  • Electrically
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4
Q

Where do we find chemical energy stores?

A
  • food
  • fuels
  • batteries
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5
Q

Where do we find kinetic energy stores?

A

-in a moving object

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6
Q

Where do we find gravitational energy stores?

A

-more in an object lifted upwards

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7
Q

Where do we find elastic energy stores?

A

-in a stretched, squashed or twisted object

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8
Q

Where do we find thermal energy stores?

A

-more in an object at a higher temperature

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9
Q

Where do we find magnetic energy stores?

A

-in magnetic forces between magnetic poles

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10
Q

Where do we find electrostatic energy stores?

A

-in electrical forces between charges

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11
Q

Where do we find nuclear energy stores?

A

-in the strong forces within the atomic nucleus

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12
Q

How do mechanically energy pathways work?

A

-when physical forces act and something moves

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13
Q

How does electrically energy pathways work?

A

-when an electric current flows

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14
Q

How do by heating energy pathways work?

A

-when there is a temperature difference

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15
Q

How do by radiation energy pathways work?

A

-when EM waves travel (including sound waves)

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16
Q

How do chemically energy pathways work?

A

-when a chemical reaction happens?

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17
Q

The principle of conservation of energy?

A

• In a closed system energy cannot be created or
destroyed.
• Energy is transferred to different energy stores – it
can’t just disappear or be made from nothing!
• If we think energy is being ‘lost’ it is either being transferred and stored elsewhere or dissipated (spread out to the surroundings)
• The total energy of a closed system is ALWAYS the same, before and after, any energy transfers

—Total Input Energy = Total Output Energy

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18
Q

Useful and wasted energy?

A

-when energy is supplied to a device (input) it ca. Be transferred (output) into:

  • useful energy (the energy store you want)
  • wasted energy (the energy store you dont want)

-a device is more efficient if it transfers more input energy into useful output energy (with less wasted)

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19
Q

Efficiency equation?

A

Efficiency = useful energy output
—————— X 100%
total energy input

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20
Q

What can sankey diagrams be used for?

A
  • to show energy transfers, as well as confirm that the total input energy = total output energy
  • you can have more than one useful or wasted energy
  • they show efficiency
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21
Q

How to read sankey diagrams?

A

-wasted energy is often in the hall form of unwanted thermal or sound and dissipates into the surroundings

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22
Q

Thermal energy transfer?

A

•The transfer of thermal energy from one store to another is by an energy pathway called HEATING.
•Thermal energy will transfer from an object or area at a higher temperature to a lower temperature.
•Energy is measured in Joules (J)
•Temperature is a measure of the average kinetic energy of
an object and is usually measured in degrees Celsius (oC)
•A thermometer is used to measure temperature.
•The greater the temperature difference, the faster is the rate of thermal energy transfer.
•If the object is at the same temperature as its surroundings, there is no thermal energy transfer!

23
Q

Conduction?

A

-transfer of thermal energy through a substance (mainly solids) when it is heated

  • Particles in solids vibrate more when they are heated.
  • The closeness of the particles in a solid and the stronger bonds between them allow these vibrations (and energy) to get passed on from particle to particle.
  • Extra particle vibration causes expansion
  • Conductors transfer this energy easily
  • Insulators do not transfer energy easily
24
Q

Why are metals not good conductors?

A

-Insulators (mainly non-metals) don’t have these ‘free’ electrons to pass on the energy faster! They can only do it by the vibrating particles alone.

  • Liquids do not conduct heat well because the bonds between the particles are weaker!
  • Gases can’t conduct heat as the particles are too far apart!
25
Q

Convection?

A

-transferring thermal energy through a fluid (liquid or gas) when particles in a warmer region gain energy and move into cooler regions, carrying this thermal energy with them

-Warm fluids rise up because they are less dense than cooler fluids
-Convection currents are set up
-In this way the thermal energy is
transferred throughout the fluid.
-Convection cannot take place in solids because the particles are not free to move to flow elsewhere.

26
Q

Examples of convection?

A
  • Heating water in a saucepan users convection (conduction causes the thermal energy to be transferred through the metal base initially).
  • Air movement, such as winds and breezes is due to warm air rising and cool air sinking, due to changing densities.
  • Convection heats up rooms and it explains why central heating hot water tanks are higher up in a house, as hot water rises!
27
Q

When hot liquids and gases rise…?

A
  • They become less dense!
  • When the particles of the fluid gain energy they move apart more and the fluid expands.
  • There are now less particles in the same volume – meaning the fluid has becomes less dense and rises.
  • Away from the heat source the particles lose energy and the fluid contracts. This makes it more dense, so the fluid sinks. This sets up a convection current in the fluid which repeats the process of energy transfer.
28
Q

Practical heating demonstrations?

A
  • The difference in the rate of thermal energy transfer by conduction in metals can be demonstrated in many ways. Copper is the best conductor, followed by aluminum, brass and iron/steel.
  • Non-metals are very poor!
  • Using dyes or potassium permanganate crystals to colour the clear water can show convection currents in liquid.
29
Q

Infrared radiation?

A
  • Thermal energy can be transferred by a type of electro-magnetic radiation called Infrared (IR) Radiation
  • All objects emit and absorb infrared (thermal) radiation
  • No medium is needed to transfer this energy through (such as with conduction and convection) – it can travel through the vacuum of space, in straight lines at the speed of light (i.e. from the Sun)
  • You can’t see this thermal radiation but you can feel and sense it!
30
Q

‘Seeing’ infrared radiation?

A
  • Infrared has no colour, but a computer can put a false colour on the special thermal camera images so we can ‘see’ the object.
  • The colours are put on a scale which corresponds to temperature. White, yellow and red usually represent the warmest areas; green, blue and black usually represent the coolest. These are called THERMOGRAMS
31
Q

Emission and absorption?

A
  • All objects emit (give out) and absorb infrared (take in) infrared radiation
  • Hotter objects emit more infrared radiation than a cooler one.
  • An object that is hotter than its surroundings emits more radiation than it absorbs (as it cools down).
  • An object that is cooler than its surroundings absorbs more radiation than it emits (as it warms up).
  • The bigger the difference in temperature between an object and its surroundings, the faster the thermal energy is transferred
32
Q

Dark, dull surfaces emit…..

A

MORE infrared radiation

33
Q

Light, shiny surfaces emit…..?

A

LESS infrared radiation

34
Q

Dark, dull surfaces absorb…..?

A

MORE infrared radiation

35
Q

Light, shiny surfaces absorb…..?

A
  • LESS infrared radiation

- they also tend to reflect more too

36
Q

Do cold surfaces absorb more IR?

A
  • Yes
  • Cold surfaces will absorb more IR from the warmer surroundings, but a dark, dull surface will absorb more than a shiny, light surface
37
Q

Do hot surfaces emit IR?

A
  • Yes
  • Hot surfaces will emit more IR to the cooler surroundings, but a dark, dull surface will emit more than a shiny, light surface
38
Q

Practical heating demonstrations?

A

• A Leslie cube will show how different surfaces at the same temperature emit different amounts of radiation.

From highest to lowest sensor temperature:

  1. Dull Black
  2. Shiny Black
  3. Dull White
  4. Shiny White

• Plotting a cooling curve from two cans of hot water shows the black surface emits radiation quicker

39
Q

Conduction occurs mainly in…?

A

SOLIDS

40
Q

Convection occurs mainly in…?

A

LIQUIDS AND GASES

41
Q

Infrared radiation occurs mainly in…?

A

HEAT WAVES

42
Q

Thermal insulators?

A
  • Some materials are very poor conductors of heat. These are called thermal insulators.
  • Examples of materials that are insulators include plastics, wood, ceramics and air.
  • Air becomes a very effective insulator when it is trapped and stopped from moving and taking energy away.
  • This is how your clothes keep you warm – air is trapped between the fibres and so acts as an insulator.
  • Other insulating materials, including polystyrene and loft insulation, use trapped air because it is so effective.
  • Poor house insulation loses energy, costs more and means more CO2 is produced when generating energy.
43
Q

Typical thermal energy loss from houses?

A
  • roof =20%
  • windows =12%
  • doors = 4%
  • floor 28%
  • walls 36%
  • home insulation can reduce these losses
44
Q

How can you stop thermal energy from getting out and how does insulation work?

A
  1. Windows – Double glazing reduces conduction
  2. Doors – Draught excluders reduces convection
  3. Walls – Cavity walls with foam insulation - reduces conduction and stops convection in between
  4. Floors – Carpets – reduces conduction
  5. Roof – Loft insulation – reduces conduction

-Insulators are poor conductors of thermal energy and reduce energy
transfer by heating.

-Use of white or shiny surfaces can reduce heat loss by radiation

45
Q

Work done = energy transfer?

A

• When an object is moved by a force, energy is transferred to it and its energy store is increased.
• Moving an object increases its kinetic energy store
• Lifting an object increases its gravitational potential energy
store
• Stretching or squashing an object increases its elastic
potential energy store
• In Physics, we say WORK is DONE on the object.

46
Q

Work done equation?

A
  • work done (W) = force (F) x distance moved (d)
  • W=Fd
  • W= work done (J)
  • F= force (N)
  • D= distance moved (m)

-F=W/d OR d=W/F

47
Q

Work done against friction?

A

• When you push an object across a surface, there is an opposing force of friction resisting you.
• You need to do extra work to overcome this friction!
• Multiply the friction force (N) by the distance moved (m) and you can calculate the work done against friction (J).
• Work is done against air resistance (air friction) as well
• Work done against friction is mainly transferred to
thermal energy stores by heating and then dissipates to the surroundings

48
Q

Gravitational potential energy?

A

• When you lift up an object, work is done (energy is transferred).
• It gains gravitational potential energy.
• Remember when you use a force (F) to
move an object a distance (s), the
work done (energy transferred) W = Fd
• The force you need to apply is equal to the weight of the object (mg) and distance moved is the height change (h).
• The more weight you lift, the more energy you transfer.
• The greater the height change, the more energy you
transfer.
• Energy transferred (vertically) = weight x height change

49
Q

Gravitational potential energy equation?

A
  • GPE (GPE) = mass (m) x gravitational field strength (g) x height (h)
  • GPE = mgh
  • GPE = gravitational potential energy (J)
  • m = mass (kg)
  • g = gravitational field strength (N/kg)
  • h = height change (m)

-This can be rearranged to give:

m = GPE/gh OR h = GPE/mg OR g = GPE/mh

50
Q

Kinetic energy?

A
  • Kinetic energy is an object’s energy store due to it moving.
  • All moving objects have kinetic energy, but the amount of kinetic energy they have depends on how fast they are moving (speed or velocity) and the mass they have.
  • The more speed it moves with, the more kinetic energy it has.
  • The more mass it has, the more kinetic energy it has.
51
Q

Kinetic energy equation?

A

-Kinetic Energy (KE) = 1⁄2 x mass (m) x speed2 (v2) KE = 1⁄2mv2

  • KE = kinetic energy (J)
  • m = mass (kg)
  • v = speed (or velocity) (m/s)

-You can write 1⁄2 as 0.5 if you wish.

-This can be rearranged to give:
m = 2KE/v2 or v = √(2KE/m

52
Q

Conservation of energy?

A

• Kinetic energy (KE) and gravitational potential energy
(GPE) can transfer between each other.
• Given the assumption that no energy is lost, then when an
object is dropped from a height, it loses GPE, but gains KE • Throw an object into the air and it loses KE, but gains GPE
CHANGE IN GPE = CHANGE IN KE mgh = 1⁄2mv2
• We see this changing of energy stores all the time – with from rockets, roller coasters, pendulums, airplanes etc.

53
Q

Power=rate of work done or energy transfer?/

A

• Two people (or machines) may transfer the same amount of energy (or work done) – in joules (J), but one of them may have done this quicker!
• The rate of work done (or energy transfer) is called POWER
• The tortoise and the hare might travel the same distance –
but the hare will do it in less time, so is more powerful!
• Power can be shown in joules/second (J/s), but it also has its own unit called the watt (W)

54
Q

Power equation?

A
  • power (P) = work done (W) ÷ time taken (t)
  • P = W/t
  • Power is measured in watts (W) = joules/second (J/s)
  • P = power (W)
  • W = Work done (energy transferred) (J)
  • t = time taken (s)

-This can be rearranged to give:
W = Pt and t = W/P

Y11 PHYSICS (5 decks)

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