chapter 10- transfer of heat energy and its effects

Question 1

how does heat transfer occur between 2 objects in contact

Answer 1

the temperature of the objects must be different. heat is transferred from a hotter body to a cooler body

Question 2

state the effect of heat on the density of air

Answer 2

density of air decreases

Question 3

explain why solids are generally better conductors of heat than liquids or gases using the particulate model of matter

Answer 3

(1) the particles of a solid are more closely packed than in liquid and gas.
(2) when they are heated, they vibrate in fixed positions vigorously and are able to transfer heat quickly to the other particles due to their close arrangement

Question 4

why is an air conditioner usually placed near the ceiling

Answer 4

when the warm air is cooled by the air conditioner, it become denser and sinks. less dense warm air rises to the top. the convection currents set up can efficiently cool the room

Question 5

explain why the water heated near the base of the kettle was able to move up the upper part of the kettle

Answer 5

when water is heated, it expands and increases in volume. it becomes less dense than the surrounding water and rises

Question 6

what is the method of heat transfer that heats up water in a tank

Answer 6

(1) convection.
(2) when the water around the heating element heats up, its density decreases and rises.
(3) cooler water from the top sinks to the bottom, gets heated up and rises.
(4) this forms a convection current which goes on till the water is uniformly heated up

Question 7

advantage of using highly reflective glass as a building material

Answer 7

it is a good absorber of heat. it reduces heat gain by conduction and keeps the interior of the building cool

Question 8

disadvantage of using highly reflective glass a building material

Answer 8

glass is a bad conductor of heat. heat loss by conduction is therefore reduced. the highly reflective surface of the glass is a poor emitter of heat

Question 9

plastic-flask

Answer 9

poor conductor of heat which minimises heat loss through conduction

Question 10

vacuum-flask

Answer 10

prevents heat loss through conduction and convection

does not contain air!

Question 11

glass with silvered surfaces-flask

Answer 11

it minimises heat loss through reflection as thermal energy is reflected into the hot liquid

thermal energy-> heat

Question 12

foam support-flask

Answer 12

contains trapped air which is poor conductor. therefore it will minimise heat loss or reduce water loss by conduction