8.3 Conduction, convection, radiation, and evaporation

Question 1

define conduction

Answer 1

form of heat transfer in which thermal energy passes through a substance from particle to particle. Conduction mainly occurs in solids.

Question 2

define insulator

Answer 2

a material which is a poor thermal conductor

Question 3

define convection

Answer 3

form of thermal transfer in which thermal energy causes a substance to expand and rise. This then cools and sinks. Convection only occurs in gases and liquids.

Question 4

define convection current

Answer 4

the movement of particles in fluid due to convection

Question 5

define fluid

Answer 5

a substance that can flow from one place to another - a gas or liquid

Question 6

define radiation

Answer 6

form or energy transfer in which thermal energy is released as infrared radiation. There is no change in matter for energy to transfer in this way.

Question 7

define absorb

Answer 7

take in energy

Question 8

define emit

Answer 8

give out energy in the form of radiation

Question 9

define evaporation

Answer 9

when a liquid turns into a gas, at a temperature lower than the boiling point. An evaporating liquid takes energy with it and so it cools the surface it was evaporating on.

Question 10

Why are frying pans made out of metal

Answer 10

Metals are good conductors of heat. So, they can heat up and cook the food a lot faster than other materials.

Question 11

Why are pan handles made of plastic or wood and not from metal

Answer 11

Plastic and wood are insulators. As they do not conduct heat very well, the person using the pan will not get burned when touching the handle of the pan

Question 12

To keep warm, you are told to wear several layers of clothes. This traps air between the layers. Why is this good at keeping you warm?

Answer 12

Multiple layers trap warm air in between the layers, acting like an insulator. So, it helps you keep warm.

Question 13

Why are solids the best conductors?
Why are gases the worst conductors?

Answer 13

Since the particles in solids are closer, it is fast at transferring energy between the particles.
As gases have a lot of space between each particle, the energy takes longer to transfer between particles.

Question 14

When liquids and gases are heated, their particles start moving around faster. What does this do to the distance between the particles?

Answer 14

The distance between the particles is decreased as they bump into each other a lot more often.

Question 15

When a fluid is heated, what happens to the density of the liquid or gas?

Answer 15

They are less dense. Because the particles move around more and spread out.

Question 16

Why does convection happen in liquids and gases, but not in solids?

Answer 16

Because for convection to take place, the molecules in the substance should be free to move. In solids the particles are packed together, so there isn’t space for the particles to move.

Question 17

Why can’t convection happen in a vacuum

Answer 17

There are no particles in a vacuum, so convection cannot happen

Question 18

Why can you feel the warmth from a fire if you are standing sideways to it?

Answer 18

The thermal radiation of the fire spreads out in all directions, so you will be able to feel the warmth from sideways.

Question 19

Why does the heat from the Sun not reach us by conduction or convection?

Answer 19

There is vacuum in between the Earth and the Sun, so conduction and convection cannot take place.

Question 20

What are the ways that a vacuum flask keeps hot liquids hot, and cold liquids cold?

Answer 20

Plastic cap (Insulator)
Silvered surfaces (silvered surfaces are good reflectors of heat)
Vacuum between the glass walls

Question 21

Difference between evaporating an boiling?

Answer 21

Evaporation is slow, occurs at all temperatures, and does not produce bubbles.
Boiling is quick, occurs at a fixed temperature, and bubbles are formed throughout the liquid.