Ch # 08 Transmission of heat

Question 1

Define thermal energy ?

Answer 1

The kinetic energy of particles in matter is called thermal energy.

Question 2

In which direction heat flows?

Answer 2

Heat flows from an object at higher temperature
to an object at lower temperature.

Question 3

Define transmission of heat?

Answer 3

The transfer of heat energy from one object to the other is called transmission of heat.

Question 4

Define conduction?

Answer 4

The transfer of heat through matter without the actual movement of particles from their position is called conduction.

Question 5

Define bad conductor?

Answer 5

Materials which do not allow heat to flow through them easily are called bad conductors

Question 6

Bad conductors also called?

Answer 6

Heat insulators

Question 7

Define good conductor?

Answer 7

Materials which allow heat to flow through
them easily are called good conductors of heat.

Question 8

Define molecules?

Answer 8

All solids (metals and non-metals) are made of tiny particles called molecules.

Question 9

How heat energy is transferred in metals?

Answer 9

In metals, heat energy is transferred from one
place to another both by the vibrations of particles as well as by the movement of free electrons.

Question 10

Why the process of conduction in liquids and gasses is slow than solids(metals) ?

Answer 10

The process of conduction in liquids and gases is very slow as compared to solids (metals). The particles in liquids and gases are not held closely together.

Question 11

Hint used in Everyday Applications of Conduction of Heat?

Answer 11

Bibi put

Question 11

Hint used in Everyday Applications of Conduction of Heat?

Answer 11

Bibi put

_Birds feathers
_Ice is covered with jute rugs
_Blankets and woolen clothes slow down transfer of heat
_Insulating material is filled between the double
walls of a refrigerator.

_double-PAN windows are used
_cooking UTENSILS
_Thermos bottles

Question 12

Define convection?

Answer 12

The transfer of heat in which molecules of a medium actually
move to the source of heat energy to absorb heat and then
move away from it, is called convection.

Question 13

Define convection current?

Answer 13

The upward and downward movement of molecules of water or
air is called a convection current.

Question 14

Why convection is not possible in solids?

Answer 14

Convection occurs in liquids and gases only because their
molecules can move freely. The molecules of a solid are held
closely together. They cannot move freely, therefore, convection
is not possible in solids.

Question 15

What is advantage of gliding flight of bird?

Answer 15

They enjoy gliding. During gliding flight a bird does not move its wings, but glides on air currents. A lot of energy of birds is saved during gliding.

Question 16

List the Everyday Applications of Convection Currents?

Answer 16

Household ventilation
Domestic water heater
Air conditioner

Question 17

Define radiation?

Answer 17

The transfer of heat energy from a hot body to a cold body directly, without heating the space in between the two bodies is called radiation.

Question 18

Why black surface is a Good absorber and good radiator?

Answer 18

Because black surface absorb most of the radiations.

Question 19

Hint of Everyday Applications of Radiation of Heat?

Answer 19

Fsc P(Pakistan)

Fire
Summer days
Cooling fins

Plastics

Question 20

Hint of Vaccum flask?

Answer 20

Carpals Mat

Container
Air between glass walls
Reduce the rate of transfer of heat
Protected glass bottle by fixing it in a metal
Amount of heat is lost by conduction
Lost by conduction
Silvered and smooth glass walls prevent transfer of heat

Metal bottles
Aluminium on the vacuum side
Three ways transfer of heat.