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Solved problems for the chapter:

Conduction, Convection and Radiation

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Thermal Expansion

1. Linear expansion

2. Cubic expansion

3. Forum

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Heat Energy

1. Heat

2. Difference between temperature and heat

5. Calculation of heat quantity

5.1. Specific heat capacity

5.2. Thermal equilibrium

6. Forum

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Heat Transfer

1. Methods of heat transfer

2. Heat conduction

2.1. Heat flow rate

2.2. Thermal resistance

3. Heat radiation

4. Forum

↓ Show theory [3] ↓

Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:conduction%2C_convection_and_radiation/3533/

Example 1.

On a chilly day, both a metal front-door knob labelled X and a similar plastic knob labelled Y are exposed to the same temperature. Which knob feels colder to the touch and why?

	knob	why
A	X	X is a worse conductor than Y
B	X	X is a better conductor than Y
C	Y	Y is a worse conductor than X
D	Y	Y is a better conductor than X

Example 2.

In which of the following does thermal conduction not occur?

Gas
Liquid
Solid
Vacuum

A night storage heater contains a large block of material that is heated electrically during the night. During the day the block cools down, releasing thermal energy into the room. Which thermal capacity of the block and which night-time temperature increase will cause the most energy to be stored by the heater?

	thermal capacity	night-time temperature increase
A	high	high
B	high	low
C	low	high
D	low	low

A metal rod is heated at end X.

Why does end Y of the metal rod become hot?

Energy is transferred from end X of the rod to end Y by movement of positive ions only.
Energy is transferred from end X of the rod to end Y by the vibration of positive ions and by the movement of electrons.
Energy is transferred from end X of the rod to end Y by movement of electrons only.
Energy is transferred from end X of the rod to end Y by vibration of positive ions only.

The metal surface of a kettle is hot. When the cool air outside the kettle comes into contact with the hot kettle, what happens to it?

The density of the air increases, and the air rises.
The density of the air increases, and the air falls.
The density of the air decreases, and the air rises.
The density of the air decreases, and the air falls.

The diagram below shows a pan used for cooking.

Which option is correct for the materials used to make the base and the handle of the pan?

	base of pan	handle of pan
A	good thermal conductor	good thermal conductor
B	poor thermal conductor	poor thermal conductor
C	poor thermal conductor	good thermal conductor
D	good thermal conductor	poor thermal conductor

In which substances is convection a method of thermal energy transfer?

air, water and wood
air and water only
water only
air only

A glass contains an iced drink on a warm and humid day. Water starts to form on the outside of the glass.

What is the name of the effect by which the water forms?

condensation
conduction
evaporation
convection

The diagram below shows a convection current caused by placing a piece of ice in a beaker of water at room temperature.

Which row correctly compares the temperatures and densities at water points P and Q?

	temperature at P	density at P
A	higher than at Q	lower than at Q
B	lower than at Q	lower than at Q
C	lower than at Q	higher than at Q
D	higher than at Q	higher than at Q

10.

There are solar water panels on the roof of a house The solar water panels contain metal pipes. The panels absorb energy from the Sun to heat up the water in the metal pipes. Which row describes how energy is transferred from the Sun and through the metal of the pipes?

	from the Sun	through the metal of the pipes
A	radiation	conduction
B	radiation	convection
C	conduction	conduction
D	conduction	convection

11.

A teacher puts some cold water in a test-tube. She holds the bottom of the test-tube while heating the top. The water at the top boils but she continues to hold the test-tube as the bottom remains cold. Which conclusion about water is made from this experiment?

Experiment

Water is a good conductor.
Water is a good convector.
Water is a bad conductor.
Water is a bad convector.

12.

Which method of transfer of thermal energy is caused by changes in density?

evaporation
conduction
radiation
convection

13.

Four thermometers, with their bulbs painted different colours, are placed at equal distances from a radiant heater. Which thermometer shows the slowest temperature rise when the heater is first switched on?

shiny black
dull black
dull white
shiny white

14.

Vacuum flasks usually have silvered walls that help to keep the contents of the flask hot. Why are the walls silvered?

to reflect thermal radiation back into the flask
to reduce energy loss to the surroundings by conduction
to absorb thermal energy from the air around the flask
to increase the rate of convection inside the flask

15.

Four beakers containing equal volumes of water at 10C are placed outside in full sunshine on a hot day.The four beakers are identical except for their surface colour and texture. Which beaker will heat up the quickest?

16.

There are two identical shiny metal containers. The outside of one of the containers is painted dull black, They are filled with equal masses of hot water at the same temperature. Why does the water in the dull black container cool more quickly?

Black surfaces are better emitters of radiation than shiny surfaces.
Black surfaces are better conductors than shiny surfaces.
Black surfaces are worse absorbers of radiation than shiny surfaces.
Black surfaces are better reflectors of radiation than shiny surfaces.

17.

Two square sheets of metal of the same material, X and Y, are heated to the same temperature. The metal sheets are shown below.

Sheet Y is emitting more radiation than sheet X. Give the reason for this.

Dull black surfaces are better emitters of radiation.
White surfaces are better absorbers of radiation.
Dull black surfaces are better conductors of radiation
The surface area of Y is larger than that of X.

18.

In which does thermal conduction not occur?

a gas
a liquid
a vacuum
a solid

19.

Four cubic copper containers are filled with water. The surfaces of all the containers are painted black. Two of the containers have sides of length and the other two containers have sides of length . Two of the containers contain water at 80C and the other two contain water at 30C. Which of the containers radiate energy at the lowest rate?

20.

Four cups A, B, C and D contain hot coffee. Which cup keeps the coffee warm the longest?

	the outer surface of the cup	the top of the cup
A	black	no lid
B	white	covered with a lid
C	black	covered with a lid
D	white	no lid

21.

One end of a copper bar is heated to a high temperature. Which mechanism(s) are responsible for the transfer of thermal energy to the other end of the copper bar?

the lattice vibrations of copper ions only
the movement of high energy copper ions along the bar
the movement of high energy electrons along the bar only
the lattice vibrations of copper ions and the movement of high energy electrons along the bar

22.

Some surfaces are better at emitting radiation than others.

Describe an experiment to show whether a black surface or a white surface is a better emitter of radiation.
To ensure that the conclusion reached out in the experiment above is correct, several details of the experiment must be identical when testing the two surfaces. State two quantities that was described that must be identical in the experiment.

23.

Some hot water is sealed inside a metal can. The can is in a vacuum in outer space. The hot water slowly cools down. How does the thermal energy escape into space?

24.

A liquid is heated and it expands. How is a convection current formed through this?

25.

An aluminium saucepan with a plastic handle contains cold water. State why the pan is made from aluminium but the handle is made from plastic.

26.

There are four materials: aluminium, wood, plastic and iron. State all materials that are electrical insulators.

27.

An aluminium saucepan is filled with cold water and placed on a hot plate. The hot plate is switched on and, as the temperature of the water in the saucepan increases, the internal energy of the water increases.

State what is meant by an increase in internal energy.
Eventually, the water reaches boiling point. Thermal energy from the hotplate is still being transferred to the water. Explain, in terms of molecules, the effect of this thermal energy on the water during boiling.

28.

A student has a block of solid metal at room temperature. The metal block emits thermal radiation from its surface. State two features of a surface that is a good emitter of thermal radiation.

29.

The diagram below shows a cross-section of a double-glazed window in the room.

What are the main methods of thermal energy transfer from the room to the outside which are reduced by this type of window?

30.

A teacher fills a copper can with solid wax and heats the can. She measures the temperature of the wax every minute. She continues heating the wax until it starts boiling. State the term used for the process that transfers thermal energy through the copper.