Year 9 - Chapter 2 -Energy transfer by heating

Question 1

What experiment do you use to test good and bad conductors and insulators of heat?

Answer 1

Wax on the end of rods in different materials. Heat up together the ends without the wax - if the wax melts it is the BEST conductor.

Question 2

What is thermal conductivity

Answer 2

the rate at which thermal energy (heat) is transferred through a material.

Question 3

What does energy transfer through materials depend on?

Answer 3

• temperature
• thickness
• thermal conductivity of the material

Question 4

What is a better conductor
a. copper or steel
b wood or glass

Answer 4

copper

glass

Question 5

Materials that are good insulators keep us _______ = materials that have LOW/HIGH thermal conductivity
This means energy transferred through them is______________.

Answer 5

1 warm
2 low
3 low

Question 6

When a substance is heated it’s temperature will depend on

Answer 6

• the amount of energy supplied to it
• mass of the substance
• what the substance is

Question 7

The greater the MASS of an object the more FASTER/SLOWER its temperature increases as its heated

Answer 7

SLOWLY

Question 8

Ways to reduce the rate of energy transferred from a home (reduce your heating bill)

Answer 8

1. Thicker bricks with lower thermal conductivity.
2. Double glazed windows
   3 Aluminium foil between a radiator panel and the wall. It reflects heat radiation away from the wall.
3. Draught excluders
4. cavity wall insulation - gap between inner and outer wall is filled with insulting leads. It traps air to act as an insulator
   6 Solar panels - absorb radiation

Question 9

Explain why an iron has a plastic handle and a metal base

Answer 9

plastic is a poor conductor of energy conductivity (or is a good insulator)
so the handle does not become hot when the iron is hot
the base is metal because metal is a good conductor of energy (or has high thermal conductivity)
and it has a low specific heat capacity so it becomes hot quickly to iron your clothes

Question 10

Explain why fitting layers of insulation in the loft of a house saves money

Answer 10

the layers of insulation reduce energy transfer by conduction from the inside of the house to the outside
so less energy from the heating system is needed to keep warm and therefore energy bills are reduced

Question 11

Explain why wrapping a block of icecream in paper helps to stop it melting

Answer 11

paper is a poor conductor of energy (or has low thermal conductivity, or is a good insulator) so it reduces energy transfer from the surroundings to the ice cream

Question 12

Explain why woolly clothing is very effective at keeping your head warm in winter

Answer 12

wool good insulator as fibres trap dry air which is good insulator inside of clothing becomes warm due to radiation from body. Body stays warm because clothing does not conduct heat energy away.

Question 13

Wearing a hat in winter is a very effective way of keeping your head warm. Describe how a hat helps to reduce the rate of energy transfer from your head

Answer 13

in cold weather, radiation from exposed skin causes energy transfer from head
hair is insulator containing trapped air so reduces energy transfer by conduction
wearing hat reduces radiation from exposed parts of scalp and reduces conduction by providing extra insulation

Question 14

Describe how to check a saucepan is hot without touching it or using a thermometer?

Answer 14

use an infrared detector
the hotter the saucepan, the
more radiation emitted

Question 15

A new type of bed warmer is sealed, filled with polymer gel, and heated using an electric insert. The bed warmer can control the temperature of the polymer gel. Suggest three advantages of using the new bed warmer and not a hot water bottle.

Answer 15

avoids risk of scalding
can set temperature to desired reading
does not get too hot

Question 16

Name the three ways heat is transferred

Answer 16

radiation - gas
convection - liquid
conduction - solid