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Physics Y9 > Heating And Cooling > Flashcards

Heating And Cooling Flashcards

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1
Q

Why are wood and fibreglass good insulators

A

Non-metals , contain trapped air

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2
Q

Why is a wire gauze placed over a Bunsen burner

A

Made of metal , spreads heat energy from the flame to the substance being heated

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3
Q

What is internal energy

A

The amount of energy in an object

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4
Q

What do thermometers do

A

Measure temperature which depends on how much the particles are vibrating.

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5
Q

What is the coldest possible temperature

A

-273 degrees , absolute zero (0 kelvin)

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6
Q

What is heat

A

Total Amount of energy in an object

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7
Q

What should a sensitive thermometer have

A

Narrow base tube and a large bulb

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8
Q

What should a quick acting thermometer have

A

Bulb made of thin glass , so heat can enter easily

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9
Q

Why is a mercury thermometer good

A

Easily seen , metal - so a good conductor of heat energy , does not freeze to readily and expands evenly but it is poisonous

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10
Q

Why is alchahol a good thermometer

A

Freezes at even lower temperatures than Mercury but vaporises in hot places , which can be dangerous as the thermometer explodes.

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11
Q

How do plastic strips work

A

Change colour , often used as clinical thermometer . These and other clinical thermometers have a fine , thin scale and a very limited range because the temperature of a human being does not vary widely . However , they can be damaged or broken If used to take the temperature of very hot or very cold liquids

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12
Q

What is a temperature sensor

A

Work electronically also used to measure temperature .muses a thermistor and a data logger.

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13
Q

What is absolute zero

A

As substances get coder the the energy of the molecules get less and less . Eventually they get to the lowest possible
energy and we cannot take any more energy out , this is lowest possible temperature , absolute zero. To calculate absolute zero from Celsius , add 273. To calculate Celsius from kelvin , subtract 273

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14
Q

What is the difference between thermal energy (heat) and temperature

A

The temperature of an object depends upon how much the particles are vibrating . Thermal energy (internal energy /heat) is the total amount of energy in an object , so a warm bath will have more thermal energy because it has lots of molecules whereas as a sparkler contains a few molecules vibrating at a high temperature but with little thermal energy.

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15
Q

How is a laboratory thermometer made to measure heat

A

Used expansion of liquids to mean see the,opera tyres accurately , as liquid gets warmer it expands along the scale. There is a vacuum above the liquid so it can move easily along the tube

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16
Q

How does heat energy travel

A

From a hot object to a cold object

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17
Q

What is thermal conduction

A

The transfer of heat energy through a substance without the substance itself moving

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18
Q

Why are metals good conductors

A

Because they have free doctrines that can move easily through the structure of the metal , speeding up the transfer of energy. Conduction takes place more rapidly in metals

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19
Q

What is the process of energy transfer by conduction

A

In a hot part of a substance , the particles have more kinetic energy . The most energetic particles transfer some of their energy to particles near them . These therefore gain energy and then pass energy on to particles near to them. The energy transfer goes on through out the substance . This process takes place in all materials .

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20
Q

What are free electrons

A

Electrons not bound to any particular atom in the structure of a substance . Metals have huge numbers of free electrons and the free electrons carry electric charge as well as energy so good thermal conductors are usually good conductors of electricity .

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21
Q

What is convection

A

The transfer of heat energy through fluids (liquids and gasses) by upwards movement of warmer less dense fluid

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22
Q

How does convection work

A

Hot water expands and becomes less dense than colder surrounding water , so it floats up to the top. Colder water sinks to take its place and is then heated too. At the top , the warm water starts to cool , becomes more dense again and will begin to sink , so a circulating current is set up in water called a convection current

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23
Q

Why do substances do and when heated

A

Because the particles which they are made of have kinetic energy . As they move around more , the average distance between particles increases.

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24
Q

How do convector heaters work

A

They heat air which then floats out of the top of the heater to the top of th room. Colder air is drawn in at the bottom and is then heated . In this way , heat energy is eventually transferred to all parts of the room.

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25
Q

What is Brownian motion

A

Particles in both liquids and gasses move randomly .this is called Brownian motion . They do this because they are bombarded by other moving particles in the fluid.larger particles can be moved by light fast moving molecules . Brownian motion is the random movement of particles.

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26
Q

How do high temperatures affect Brownian motion

A

Higher temperatures lead to faster Brownian motion. If there is no preffered direction for the random oscillations particles will spread every throughout the medium they are in.

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27
Q

Where does Brownian motion occur

A

Colloidal suspension e.g solid in liquid , liquid in liquid , gas in solid . Liquid in gas . Small particles of matter suspended in fluid are moved around by the molecules of fluid. Examples are dust particle in air. The dust article seems to be moving randomly but is bing pushed around by smaller air particles

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28
Q

What is the velocity of Brownian motion proportional to

A

The molecules are in constant irregular motion with a velocity proportional to the square root of the temperature of the medium they are in .

29
Q

How does a bimetallic strip work

A

Strip made of brass and iron . Brass expands more than iron , so when heated the strip will bend away from flame .

30
Q

How do liquids in capillary tubes work

A

Test tubes of oil , water and glycerol placed in a beaker of water and heated. The liquid expands when heated and moves up the capillary tube . Oil expanded the most then water then glycerol.

31
Q

How does the ball and ring work

A

We heated the ball , the particles vibrated more and it expanded so it then could not fit through the ring.

32
Q

How does the cast iron peg and bar work

A

Thick bar is heated by Bunsen burner and the cast iron legs are tightened as it expands . When it cools down the metal bar shortens and breaks the cast iron pegs. This shows that when the bars cool you get big pulling forces. When the bars heat you get big pushing forces .

33
Q

What happens when objects cool down

A

They contract , get smaller .

34
Q

Why do substances expand

A

When they are heated particles start moving faster and take up more Space .

35
Q

What happens in the round bottomed flask and glass tube at the top

A

The round bottomed flash that has a bung with a long glass tube is placed in a beaker of hot water with a coloured liquid in the flask , the coloured liquid is sucked up the tube because there is no more space in the beaker

36
Q

Do liquids eco and more than solid

A

Yes because there are larger gaps between the particles so when they vibrate they take up more space.

37
Q

How does a glass flask with a tube being dipped into a beaker of water work

A

When hands are placed on the flask , Gas goes down the tube to the water and bubbles because the gas has expanded and can no longer fit in the flask. When hands are taken off the flask liquid flows up the glass tube because there is now more space because the gas has contracted .

38
Q

Why do bridges and roads contain expansion gaps

A

Bridges are usually out on rollers so that they can expand and contract depending on the weather without causing damage , there will also be an expansion gap in the road at the end of the bridge . Roads are often made of large concrete slabs and they you expand. There are expansion gaps between the slabs , filled with a soft substance which can be squeezed easily in hot weather .

39
Q

Why does glass crack if you put hot substances in it

A

Because the inside tries to expand while the outside stays the same size. Pyrex does not crack because it does not expand as much as normal glass.

40
Q

How do thermostat work

A

Used to keep something at the same temperature without getting to jot or to cold. Contains a bimetallic strip so that when it gets too hot the strip will bend and break contact with the current and when it gets to cold the strip will expand and break contact .

41
Q

Why do copper rods feel hot when you hold them

A

Heat is passed through the rod because as the particles get heated they start vibrating more and bump into their neighbours and pass the heat along the rod.

42
Q

How do conduction rods work

A

Heat is passed through the copper , aluminium , brass and still rods at different rates as they are all conductors . Conduction rods have an indicator that shows how far the heat has been passed

43
Q

How do ball bearing and wax work

A

As the rods get heated they conduct energy along and the heat of the rod melts the wax and drops the ball bearing . The copper dropped first , then aluminium , then brass , then iron.

44
Q

How does the wood , paper and brass test work

A

Wood is an insulator , whereas brass is a conductor . Because wood is an insulator it does not pass heat along the wooden block , so the paper is burnt on the wooden side instead of the brass side because the heat is absorbed through the brass not the paper

45
Q

How does the ice and water test show water does not conduct heat

A

Water is heated and begins to boil however the ice , held in place by gauze, does not melt because liquid is not a good conductor and the heat is not passed down through the water to the ice .

46
Q

How is a convection currents shown in liquid with coloured crystals

A

As the coloured liquid becomes heated it becomes less dense and rises to the surface and the colder liquid sinks and replacing it .

47
Q

How is convection current shown in the gass chimney experiment

A

Using a smoke match , put it inside the gas chimney . The smoke will move down the chimney become heated by the candle and rise up creating a convection current.

48
Q

How are reverse conduction currents used in a fridge

A

Cold air in the Fridge sinks due to cooling element at the top cools the air and it becomes more dense than the less cooled air and sinks to the bottom. Less cooled air then rises becomes cooled and sinks creating a reverse convection current.

49
Q

How do solar ovens work

A

Infa red rays from the sun are reflected by a large concave mirror and focused on a kettle or pan for cooking .

50
Q

How do greenhouses work

A

Rays from the very hot sun have a short wavelength which can get through the glass. These rays are absorbed by the plants which get warmer and also radiate infra red Rays . However because the plant is not very hot the rays have a longer wavelength and cannot get through the glass so energy is radiated in but cannot easily radiate out

51
Q

How does a thermos flask keep tea hot

A

It stops conduction, convection and radiation. It is a double walled glass bottle. In the space between the two walls both pieces of glass or coated with shiny bright silvering and the air is pumped out to form a vacuum. The vacuum stops energy transfer. By stopping conduction and convection. The silvering on one glass wall reduces radiation of energy and the silvering on the other glass wall reflects back any infrared rays that may have been radiated. It also has a cork or plastic stopper that contains a lot of trapped air , a bad conductor .

52
Q

How do you investigate whether the colour of a container affects the rate if cooling

A

I boiled the kettle , then poured the hot water into the black can, filling it to the top. I will then place the timer on 10 mins and measured the temperature of the water every 30 seconds , using the thermometer . I then repeated the test but used a silver can . The black can cooled the fastest.

53
Q

How does a penny and wax experiment show radiation

A

We had a black tin lid and a silver tin lid with a penny stuck on both with wax. We heated them both and the wax melted and the penny dropped off the black tin lid first because black is better than sliver at absorbing radiation from the Bunsen burner.

54
Q

How does Leslie’s cube show radiation

A

Leslie’s cube has a white surface and a black surface . We filled it with Hot water. The sides of the cube emitted infrared because they are hotter than the air. We used an infra red detector to measure . the black surface had a higher infra red reading than white showing black emits more infra red.

55
Q

What surfaces are good reflectors of thermal radiation and good absorbers

A

Ir waves can be reflected and Absorbed by different materials, just like visible light. Highly polished shiny surfaces are good reflectors of thermal radiation. White surfaces also reflect a lot of IR . Matt black and dark surfaces are poor reflectors but good absorbers of heat radiation and are useful to use on solar panels to absorb the heat . If a surface is a good reflector it will be a poor absorber. This means that a hot object with a shiny surface will Admit less heat energy in the form of IR than a dull black surface . Thermal radiation. N be felt almost instantly.

56
Q

How does heat travel during radiation

A

Heat travels in the form of waves like visible light . Heat waves are called infra red waves and are part of the electromagnetic spectrum and gave the Same properties as light waves . They can travel through a vacuum and does so at the speed of light

57
Q

Why is it important that IR waves can travel through a vacuum at the speed of light

A

Because other wise we would not recieve heat from the sun.

58
Q

How do windows loose heat and how can they be insulated

A

By convection , conduction and radiation . Curtains reduce energy losses by all three because the curtain creates a space between the window and the room .double glazed windows also reduce energy losses because the air in the gap is a poor conductor of heat and there is little space for convection l

59
Q

How does a roof loose heat and how can it be insulated

A

Conduction and then convection . Conduction through the ceiling and the roof itself and then by convection . This can be prevented by lagging the loft floor and insulating the roof will reduce energy losses considerably

60
Q

How do walls loose heat and how can we insulate the,

A

By conduction and then convection . Cavity wall insulation as it reduces the rate of which energy is conducted and escaped through the walls. Foil placed behind radiators reflects energy back into the room instead of letting it escape through the walls because the silver surface is a bad absorber .

61
Q

How do draughts loose heat and how can they be prevented

A

By convection carpet and draught excluders.

62
Q

What can increase energy loses n your house

A

Windy and rainy weather increase the rate of energy loses

63
Q

How can energy losses be reduced

A

Insulation keeps houses warm in winter and cool in summer

64
Q

Why do ir waves from the sun have short wavelength

A

Because they come from such a hit source and are very energetic , the ir radiation passes through space until it hits something solid, when the Rays hit the solid the energy is then released and the solid warms up and then gives out lower less energetic waves . The energy will the build up in a closed space and temperature rises . If curtains in a room are closed on a hot day the room will be cooler .

65
Q

Why does your body lose heat more quickly in wet clothes

A

Water conducts heat away from your body .

66
Q

Why is conduction slow In gasses

A

Because the molecules are spread so widely

67
Q

Why will a heat transfer be greatest in the beginning

A

When a heat difference is biggest , the transfer will have more kinetic energy and will therefore be the greatest.

68
Q

Why is it bad to throw aerosol in a bonfire .

A

Compressed gas , Which will burst when heated .

69
Q

What are the worse conductors of heat

A

Gasses

Physics Y9 (4 decks)

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