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GCSE Physics (P1) > Energy Transfer by Heating > Flashcards

Energy Transfer by Heating Flashcards

1
Q

How can we detect infrared raditation?

A

With our skin - it makes us feel warm

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2
Q

What do all objects do?

A

Emit radiation

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3
Q

The hotter an object is…

A

…the more infrared radiation it emits in a given time

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4
Q

What is a vacuum?

A

A region that doesn’t contain any particles.

Conduction and convection cannot occur here, but radiation can

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5
Q

What does the transfer of energy by infrared radiation not involve?

A

Particles

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6
Q

What type of surfaces are good absorbers of radiation?

A

Dark-coloured, matt surfaces

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7
Q

If an object is a good absorber of radiation, we also know that it will be a good…

A

..emitter too. Physics works both ways!

The same is true of reflectors, they are also poor absorbers

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8
Q

What type of material is a good reflector and poor absorber of radiation?

A

Light-coloured, shiny surfaces

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9
Q

What are the properties of solid particles?

A
  • Low transactional energy, but still vibrate (vibrational energy)
  • Fixed positions due to strong intermolecular bonds
  • Fixed + rigid shape
  • Not compressable
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10
Q

What are the properties of liquid particles?

A
  • Lower energy than gas, higher than solid
  • Particles still in contact with each other due to fairly strong intermolecular bonds
  • Can move around slightly and form random arrangements
  • Therefore, can flow and fit shape of container
  • Does not have a fixed shape
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11
Q

What are the properties of gas particles?

A
  • High energy (high transactional)
  • No fixed positions due to very weak intermolecular bonds
  • Therefore they can move randomly and much faster
  • No fixed shape and can flow
  • Compressable
  • Much less dense than solids + liquids
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12
Q

Draw a diagram showing the different states of matter

A
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13
Q

When does conduction occur?

A

In solids (and poorly in liquids)

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14
Q

What types of material are the best conductors and why?

A
  • Metals are the best conductors.
  • This is because they contain free electrons.
  • When heated, these gain energy and move through the metal, transfering energy by colliding with other particles.
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15
Q

Describe how conduction works.

A
  • When one end of a solid is heated, the particles at that end gain kinetic energy and vibrate more
  • These vibrations pass energy onto neighbouring particles
  • This process continues through the solid, passing on slightly less energy each time as some is maintained by each vibrating particle
  • This is how energy is transfered through a solid (conduction)
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16
Q

What are insulators?

A

A poor conductor

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17
Q

What is a conductor?

A

A material/substance that conducts energy (via conduction) well…

18
Q

Why are materials such as wool and fibreglass good insulators?

A

Because they contain trapped air.

Air is a poor conductor because it is a gas, so the particles are much less densely packed and therefore do not transfer energy by conduction very well at all.

19
Q

Where does convection occur?

A

In fluids

20
Q

What are fluids?

A

Liquids and gasses

(They can flow)

21
Q

Describe how convection works.

A
  • When a fluid is heated it expands and gains kinetic energy
  • The fluid becomes less dense and rises
  • As the fluid rises, it begins to loose some of its energy
  • This causes it to sink again and become more dense
  • It is then heated again and the process continues.
  • This forms a convection current
22
Q

What are convection currents responsible for in the real world?

A

Onshore and offshore breezes

23
Q

Why does a fluid become less dense when it is heated?

A

Because the particles gain more kinetic energy and move apart.

This causes it to expand.

This means there is the same amount of mass in a larger area.

24
Q

Why does evaportation take place?

A

Because the most energetic liquid molecules escape the liquid’s surface and enter the air/become a gas

25
Q

How does evaporation also cause cooling?

A
  • Evaportation takes place due to the most energetic liquid particles escaping the liquid’s surface and entering the air/becoming a gas.
  • This means that the average kinetic energy of the remaining molecules decreases, so the temperature of the liquid also decreases
26
Q

How can the rate of evaportation be increased?

A
  • Increasing the surface area
  • Increasing the temperature
  • Creating a draught of air across the liquid’s surface
27
Q

How can the rate of condensation be increased?

A
  • Increasing the surface area
  • Decreasing the temperature
28
Q

The greater the temperature difference between an object and its surroundings…

A

…the greater the rate at which energy is transfered

29
Q

What does the rate at which energy is transfered depend upon?

A
  • The substances/materials the object is in contact with
  • The object’s shape
  • The object’s surface area
  • The temperature difference between the object and its surroundings
30
Q

Why might we want to maximise the rate of energy tranfer?

A

To keep an object cool

31
Q

How can the rate of energy transfer be maximised?

A
  • Use good conductors
  • Use good emitters (dark, matt)
  • Maximise air flow/draught
32
Q

How can the rate of energy transfer be minimised?

A
  • Use good insulators
  • Use good reflectors (white, shiny)
  • Prevent convection currents by trapping air in small pockets (this also prevents conduction)
33
Q

Draw an label a diagram of a vacuum flask showing how it is a good insulator

A
  • Plastic cap prevents conduction + convection
  • Double-walled glass/plastic container prevents conduction + radiation00
  • Plastic protective cover prevents conduction
  • Hot/cold liquid
  • Sponge pad for protection also prevents conduction
  • Inside surfaces silvered to stop radiation
  • Vacuum prevents conduction + convection
  • Plastic spring for support
34
Q

What does a vacuum flask do and why?

A

Reduces the rate of energy transfer to keep hot things hot and cool things cool

35
Q

What is the specific heat capacity of a substance?

A

The amount of energy (Joules) required to raise 1Kg of it by 1°C (or K)

36
Q

What does the rate of temperature change in a substance when heated depend upon?

A
  • The amount of energy transfered to it
  • Its mass
  • Its specific heat capactity
37
Q

What are U-values and what do they tell us?

A

The amount of energy per second that passes through a material.

The lower the U-value, the better insulator the material is

38
Q

Why do most people want to minimise the rate of energy transfer out of their homes?

A

To reduce fuel/energy consumption, and therefore fuel/energy bills

39
Q

How can heat transfer out of homes be reduced?

A
  • Fibreglass loft insulation to reduce conduction
  • Cavity wall insulation traps air in small pockets to reduce covection + conduction
  • Double glazing reduces conduction
  • Draught proofing reduces convection
  • Aluminium foil behind radiators reflects infrared raditation back into the room and therefore reduces radiation
  • Thick curtains reduce conduction and radiation
40
Q

How do solar heating pannels work?

A
  • They contain water that is heated by infrared radiation from the Sun.
  • This water may then be used to heat buildings or provide domestic hot water.
  • The pipes that contain the water are often painted black because it both a good absorber and emitter of radiation.
41
Q

What are the benefits and drawbacks of solar heating panels?

A
  • They are cheap to run because they do not use fuel
  • They do not contribute to global warming because they do not produce greenhouse gasses when heating water

However:

  • They are expensive to buy + install
  • They do not heat water at night

GCSE Physics (P1) (6 decks)

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