Science chapter 10

Question 1

The change in temperature indicates

Answer 1

it indicates an increase in our body’s heat production.

Question 2

Temperature refers to

Answer 2

how hot or cold an object is

Question 3

Heat energy refers to

Answer 3

the amount of thermal energy that is being transferred from a hotter to a colder region

Question 4

The SI unit for temperature is

Answer 4

kelvin(K)

Question 5

The SI unit for heat energy is

Answer 5

joule (J)

Question 6

When a substance is heated, it undergoes

Answer 6

expansion

Question 7

When a substance is cooled, it undergoes

Answer 7

contraction

Question 8

When a substance is heated, it gains heat energy and

Answer 8

expands(increases in volume)

Question 9

When a substance is cooled, it loses heat energy and

Answer 9

contracts(decreases in volume)

Question 10

What causes transfer of thermal energy?

Answer 10

difference in temperature

Question 11

Thermal energy always flows from a region of

Answer 11

higher temperature to a region of lower temperature.

Question 12

There is no transfer of heat

Answer 12

at thermal equilibrium.

Question 13

Conduction is the process by which

Answer 13

thermal energy is transmitted from a region of higher temperature to a region of lower temperature from one particle to another through vibrations without any flow in the medium.

Question 14

Conduction is the only means of transfer of thermal energy in

Answer 14

solid mediums.

Question 15

How does conduction work?

Answer 15

When one end of a material is heated, particles there gain kinetic energy and vibrate faster and more vigorously.
These particles collide more frequently with less energetic neighbouring particles
causing neighbouring particles to gain kinetic energy.
These neighbouring particles vibrate faster and more vigorously and the energy is passed along to the rest of the particles in the bar.

Question 16

Why are metals good conductors of heat?

Answer 16

They have free electrons

Question 17

In non-metals, thermal energy is transferred through the

Answer 17

vibration and collision of particles.

Question 18

In metals, thermal energy is transferred through

Answer 18

the vibration and collision of particles, and the process of electron diffusion.

Question 19

In metals, electrons

Answer 19

gain kinetic energy and move more rapidly. They collide with particles in the cooler parts of the metal and pass on their energy in the process.

Question 20

Conduction of thermal energy in metals is … than in non-metals because conduction takes place through vibrating particles as well as through the free electrons present in metals

Answer 20

far better, conduction takes place through vibrating particles as well as through the free electrons present in metals

Question 21

Explain the process of free electronic diffusion

Answer 21

When heated, the free electrons gain energy and move faster
These electrons are free to travel in the spaces between the metal particles.
This process is known as free electron diffusion, it is much faster than the conduction by vibration of atoms or molecules that takes place in non-metals.
Hence, metals conduct thermal energy much faster than non-metals which have no free electrons.

Question 22

In conduction, thermal energy is transferred from one particle to another.

Answer 22

from one particle to another

Question 23

Convection is the process by which

Answer 23

thermal energy is transmitted from one region to another in a fluid (liquid or gas) by the circulation of currents that direct the movement (flow) of the particles of the fluid.

Question 24

In convection, thermal energy is transferred

Answer 24

through the actual movement of the heated particles from the warmer to cooler parts of the fluid.

Question 25

Explain convection in liquid

Answer 25

When the water at the bottom of the flask is heated, it expands.
The expanded water is less dense than the surrounding water and rises.
Since the upper region is cooler, it is denser and therefore sinks.
The difference in the densities of water in the different regions sets up a convection current.
This is shown by purple streams rising from the bottom and sinking at the sides.

Question 26

Explain convection in gas

Answer 26

When the air above the candle is heated, it expands.
The expanded air is less dense than the surrounding air and rises out of chimney B.
Since the surrounding air is cooler, it is denser and therefore sinks into chimney A.
The difference in the densities of the air at the different chimneys sets up a convection current.

Question 27

What is radiation

Answer 27

it is the transfer of thermal energy in the form of electromagnetic waves such as infrared radiation without the aid of a medium.

Question 28

Where can radiation be taken place in?

Answer 28

Radiation can take place in a vacuum. This is how the Earth is warmed by the Sun.

Question 29

Do All bodies emit infrared radiation?

Answer 29

YAS

Question 30

Factors that affect the rate of emission and absorption of radiation

Answer 30

Temperature, Surface area to volume ratio, Colour and texture

Question 31

Objects with a … emit heat at a faster rate.

Answer 31

larger surface area to volume ratio

Question 32

Rough and black stuff are

Answer 32

better emitters of heat

Question 33

Poor conductors of thermal energy

Answer 33

air and water

Question 34

Materials like … are effective insulators because they contain pockets of still air

Answer 34

polyester foam, cork, wool, and fibreglass

Question 35

Good heat insulators reduce heat by

Answer 35

conduction

Question 36

Cold air

Answer 36

sinks

Question 37

Hot air

Answer 37

rises

Question 38

Shiny and silvery or white surface reduce heat loss or gain by

Answer 38

radiation

Question 39

white uniform is commonly worn because white surfaces reflect

Answer 39

heat well and are poor absorbers of heat.

Question 40

How are land and sea breezes formed?

Answer 40

In the day, the land heats up faster than the sea. The air above the land is heated, expands and rises.
Cool air above the sea is denser and moves in to replace the warmer air. This sets up a sea breeze.
At night, the land cools faster than the sea.
The air above the land is now cooler than the air above the sea.
A convection current is set up in the opposite direction. This is called a land breeze.

Question 41

Black and dull surfaces increase heat loss by

Answer 41

radiation

Question 42

How does a vacuum flask keep the liquid it contains cool or hot?

Answer 42

Container supported by foam plastic, and covered with a plastic cap, both poor conductors of heat, hence prevent heat loss.
Consists of a double-walled glass container with a vacuum in between – prevent heat loss by conduction and convection.
Silvered walls on vacuum side – reduces heat loss by radiation as heat is release backed into the hot liquid.