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Chp 14: Effects of Heat Energy
Section B: Short Answer Questions
1)
Effects of heating:
Mass - Remains unchanged
Volume - Increases
Density - Decreases
Effects of cooling:
Mass - Remains unchanged
Volume - Decreases
Density - Increases

2)
a. These bends allow the pipes to expand or contract without cracking
b. Refer to notes on Effect of heat

3)
No. Both strips are made of similar materials and thus will expand evenly together

4)
The water freezes and forms a ‘hump’ at the brim. This is because water expands when the temperature goes below 4°C to 0°C.

Section C: Free response / structured questions
1)
Immerse the bottom of cup B in hot water and / or put ice cubes in cup A. Hot water make cup B expand and ice cubes make cup A contract, so that Jiaming can easily pry open the cups

2)
Advantages:
- Riveting
- Bimetallic strips in thermostats
- Resistance thermometer
- Hot air balloons
Disadvantages:
- Deformation of plastic bottles
- If there is no room for expansion / contraction:
o Buckled railway track
o Snap / sag overhead cables
o Cracks along roads / bridges

3)
a.
i) When the bimetallic strip is heated
ii) Upon heating, brass expands more than iron and causes the bimetallic strip to bend downwards, so that the metal contacts touch each other

b.
Fire alarm

4)
Types of thermometers - Physical properties:
Liquid-in-glass thermometer - The volume of a fixed mass of liquid changes steadily with temperature
Constant volume gas thermometer - Pressure of a fixed mass of gas at constant volume varies uniformly with changes in temperature
Liquid crystal thermometer - The liquid crystals change colours at different temperature
Resistance thermometer - The resistance of the wire varies uniformly with changes in temperature
Thermocouple thermometer - Amount of electric current flowing in the wires varies uniformly with changes in temperature
Low temperature sensor thermometer - The output voltage varies uniformly with the changes in temperature

Chapter 15: Transfer of Heat
Section B: Short-answer questions
1)
a. convection
b. radiation
c. conduction

2)
a.
Heat conductors
-Mercury
-Aluminium
-Silver
-Copper
-Tin
Heat insulators
-Water
-Air
-Wood
-Glass
-Cotton wool
b. Wood. It is a solid that can be easily crafted, has structural strength and economical.
c. The different rate of heating and losing heat on different surfaces

4)
a. A thick fur coat can trapped air which is a poor conductor of heat, so conduction of heat is greatly reduced
b. The lid stops the steam from leaving the cup and thus reduces convection of heat
c. Emission of radiant heat from the food is reflected back by the silvery surfaced aluminium foil, and thus keep the food warm longer

Section C: Free response / structured questions
1) Black surfaces are good absorbers of radiant heat. Thus solar panels are painted black to accumulate maximum heat energy
Silver surfaces are poor absorbers of radiant heat. That’s why oil tanks are painted silver so as to keep the contents cool

2)
a. The stopper is made of poor conductor material like cork. The vacuum between the double glass walls deters conductionb.
b. The stopper stops the steam in the flask from escaping to the surroundings, thus reduce convection
c. Silvered surface of double glass will greatly reduce heat loss by radiation. The exterior metal / plastic case is usually made off shiny material and light colours so as to produce heat loss by radiation

3)
a. Fill the test tube ¼ height with water
Wrap the ice cube with a piece of wire gauze and drop it into the test tube. Ice cube should sink to the bottom
Using a test tube holder, heat the top part of the test tube Observed that water boils at the top part of the test tube and the ice at the bottom melts very slowly. This shows that water is a poor conductor of heat
b. This arrangement help to improve the convection of water in the kettle as warm water expands, become less dense and rises, and cold water contracts, become denser and sinks

4)
a. Convection and radiation
b. Blow, use a fan or put it in an air-conditioned room. To increase convection
Or use a black cup

2Eternon__*]] 4:49 PM