Chapter 6 - heat transfer

Question 1

What is conduction ?

Answer 1

Heat travelling through solids

Question 2

What is convection ?

Answer 2

transfers heat only in liquids and gases

Question 3

What is radiation ?

Answer 3

the only method of heat transfer in a vacuum

Question 4

What is a conductor ?

Answer 4

A material which allows electricity to mass through it easily. Most conductors are metals.

Question 5

How does heat move in a solid ?

Answer 5

Atoms in a solid are held together by chemical bonds. The atoms vibrate and pass on heat and kinetic energy as they do so.

Question 6

Why are metals such good conductors?

Answer 6

Because all metals have free electrons to carry heat, this heat allows them to move much faster than before. As the electrons move around some collide with the atoms cause those to vibrate and the heat to be passed on.

Question 7

why are liquids such poor conductors ?

Answer 7

They have no free electrons and rely on passing vibrations from atom to atom.

Question 8

Is air a good or bad conductor ?

Answer 8

very bad

Question 9

When does convection occur?

Answer 9

It occurs when the fastest-moving particles in a hot region of a gas or liquid move to a cool region, taking their heat enrgy with them.

Question 10

In the convection experiment why does smoke fall down the chimney ?

Answer 10

• the air arounf the candle becomes very hot
• the air molecules around the candle are moving faster than those in the normal air
• The density of the hot air is lower than that of the normal air , so air rises up the chimney
• cooler air moves horizontally along the tunnel to replace air that has left
• the moving smoke follows the movement of the cold air

Question 11

Why does convection in liquids occur ?

Answer 11

• the molecules vibrate with greater amplitude
• this causes the warm water to expand
• the density of the warm water is less than the cold water
• the warm water rises

Question 12

name differnt methods to stop heat loss from a home

Answer 12

• cavity wall inslation
• loft insulatuion
• double glazing
• Thick curtains / carpets

Question 13

Which method of heat transfer does the earth get the heat energy from the sun ?

Answer 13

Radiation

Question 14

How is the energy from the sun transported to the earth ?

Answer 14

It is transferred as infrared radiation

Question 15

The hotter an object the ………. radiation it emits

Answer 15

more

Question 16

What will happen if an object is cooler than it’s surroundings ?

Answer 16

It absorbs more radiant heat than it emits, so its temperature rises.

Question 17

What surfaces are the best and worst emitters of radiation ?

Answer 17

Black surfaces : best emitters of radiation
white surfaces : worst emitters of heat

matt surfaces are better emitters than gloss surfaces

Question 18

What happens when radiant heat falls on a surface ?

Answer 18

It is partly absorbed and partly reflected

Question 19

Which surfaces are the best and worst for absorption ?

Answer 19

matt black surfaces are good absorbers and poor reflectors of radiation.

Gloss white surfaces are poor absorbers and good reflectors of radiation.

Question 20

What happens to the infrared energy from the sun when it reaches the earth ?

Answer 20

Most of it is reflected back into space.

Question 21

Give a basic explanation of the greenhouse effect.

Answer 21

The infrared energy from the earth has a longer wavelength than the energy from the sun. This long wavelength energy is absorbed by the greenhouse gases, keeping the earth warm.

Question 22

What are some consequences of global warming ?

Answer 22

• polar ice-caps melt
• extreme weather events occur
• reduction in agricultural yields
• destruction of some habitats
• increases the spread of disease

Question 23

How does solar water heating work ?

Answer 23

• Sunlight passes through glass on to a black metal sheet
• The black metal absorbs almost all the heat energy
• heat stored in the black metal is then transferred to the water flowing in the pipe attached.