Transfer of Thermal Energy

Transfer of Thermal Energy (O Level)

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Question 1
Object A is 2 kg. It has a temperature of 40oC and has an internal energy of 500000 J. Object B is 2 kg. It has a temperature of 50oC and has an internal energy of 400000 J. Which of the following statements is correct?
A
Heat flow from object A to object B.
B
Heat flow from object B to object A.
C
No heat flow between object A and object B.
D
There is not enough information to determine the direction of heat flow.
Question 1 Explanation: 
Heat will always flow from a region of higher temperature to a region of lower temperature. The direction of heat flow is not determined by the internal energy or mass.
Question 2
2 kg of ice at 0oC is floating on 5 kg of water at 0oC. Which of the following statements is true?
A
Heat flow from ice to water
B
Heat flow from water to ice
C
No heat flow between ice and water
D
There is not enough information to determine the direction of heat flow.
Question 2 Explanation: 
Heat will always flow from a region of higher temperature to a region of lower temperature. Since both ice and water have the same temperature, thermal equilibrium has reached and there will be no heat flow between them. The direction of heat flow is not determined by the state of matter or mass.
Question 3
Conduction is a transfer of thermal energy via
A
Vibration of the particles
B
Differences in densities
C
Movement of particles from one place to another
D
Radiation of wave
Question 3 Explanation: 
Conduction is a process whereby thermal energy is transferred from one point to another by vibration of the molecules. Energy is passed on from one molecule to another without the molecule moving out from their fixed position.
Question 4
Convection is transfer of thermal energy due to
A
Vibration of the particles
B
Expansion of fluid
C
Movement of particles from one place to another
D
Radiation of wave
Question 4 Explanation: 
Convection is a process whereby thermal energy is transferred from one point to another due to difference in densities. The portion of fluid with higher temperature will have a lower density. This portion of fluid will float among the cooler liquid and at the same time bring thermal energy upwards. Thermal energy is transferred by molecules moving from one place to another.
Question 5
What is radiation?
A
Transfer of thermal energy by wave which does not require a material medium
B
Transfer of thermal energy by vibration of nucleus
C
Transfer of thermal energy by the movement of free electrons
D
Transfer of thermal energy by movements of molecules due to a difference in densities.
Question 5 Explanation: 
Radiation is transfer of thermal energy by invisible electromagnetic waves. It does not require any medium to flow.
Question 6
Give a reason why Aluminium is a better conductor than wood?
A
Aluminium has a higher density than wood.
B
Aluminium has a higher specific heat capacity than wood
C
Aluminium has more free electrons than wood
D
Aluminium has a higher mass than wood
Question 6 Explanation: 
A good conductor is a kind of material with more free electrons. All metals are therefore good conductor. When a metal object is heated, the free electrons gain energy and drift towards the cooler part of the object. Therefore in a substance of more free electrons, thermal energy can be transferred more quickly.
Question 7
Conduction happens in
A
Solid only
B
Liquid only
C
Solid and liquid only
D
Solid, Liquid and gas.
Question 7 Explanation: 
Conduction happens in all matter. Conduction can take place as long as there is a medium. Rate of conduction is normally fastest in a solid and slowest in gas.
Question 8
Convection happens in
A
Liquid only
B
Gas only
C
Liquid and gas only
D
Solid, liquid and gas
Question 8 Explanation: 
Convection takes place only in fluid. Fluid refers to matters that can flow and therefore convection happens only in liquid and gas. Convection cannot take place in solid because the particles of solid are strongly bonded together and not allowed to flow.
Question 9
Which of the following statements about radiation is true?
  1. Radiation can pass through solids
  2. Radiation can pass through liquids
  3. Radiation can pass through gases
A
3 only
B
2 and 3 only
C
1 and 3 only
D
1, 2 and 3
Question 9 Explanation: 
Radiation can pass through solid. (e.g. transparent glass) Radiation can pass through liquid. (e.g. Water) Radiation can pass through gases. (e.g. Air) The higher the temperature of the heat source, the higher the frequency of the infra-red radiation it will transmit. High frequency radiation is more penetrating than the low frequency infra-red radiation.
Question 10
Which of the following heat transfer processes can take place in vacuum?
  1. Conduction
  2. Convection
  3. Radiation
A
1 only
B
3 only
C
1 and 2 only
D
1, 2 and 3
Question 10 Explanation: 
Radiation is transfer of thermal energy by invisible electromagnetic waves. It does not require any medium to transmit; therefore it can transfer thermal energy through vacuum.
Question 11
Which of the following heat transfer processes is/are caused by the movement of particles?
  1. Conduction
  2. Convection
  3. Radiation
A
1 only
B
3 only
C
1 and 2 only
D
1, 2 and 3
Question 11 Explanation: 
Conduction transfers thermal energy by the vibration of particles. Convection transfers thermal energy by the movement of the fluid particles. Radiation is a transfer of thermal energy by electromagnetic waves. It does not require any particles.
Question 12
Which of the following about conduction is/are true?
  1. Conduction can transfer thermal energy faster in denser medium.
  2. Conduction cannot happen together with convection.
  3. Conduction can transfer thermal energy faster through good electrical conductors.
A
1 and 2 only
B
1 and 3 only
C
2 and 3 only
D
1, 2 and 3
Question 12 Explanation: 
Conduction transfers thermal energy by the vibration of particles. The closer the particles are packed together, the more quickly it is for the energy to pass from one particle to another via vibration. When a good conductor is heated, its free electrons gain energy and drift towards the cooler part of the object. Since a good electrical conductor contains many free electrons, good electrical conductor is a good thermal conductor. Conduction can occur in all media. Convection happens in fluid. Conduction and convection therefore can happen simultaneously in fluids. Fluid is normally a bad conductor but it is still able to conduct.
Question 13
The white porcelain lid of a cup of hot drink is to
  1. reduce loss of thermal energy by evaporation.
  2. reduce loss of thermal energy by radiation.
  3. reduce loss of thermal energy by convection.
A
1 and 2 only
B
1 and 3 only
C
2 and 3 only
D
1, 2 and 3
Question 13 Explanation: 
White colour is a bad absorber of radiant heat. It reflects radiant heat back into the cup of water. The lid acts as a cover to prevent vapour going out of the cup due to evaporation, and warm air to go out of the cup because of convection. It helps to trap thermal energy within the cup.
Question 14
The wooden handle of a pot
A
Prevents the transfer of thermal energy by conduction to the hand.
B
Reduces the transfer of thermal energy by conduction to the hand.
C
Prevents the transfer of thermal energy by radiation to the hand.
D
Reduces the transfer of thermal energy by radiation to the hand.
Question 14 Explanation: 
Wood is an insulator. It helps to reduce the rate of conduction flowing to the hand. The word ‘prevent’ is not the right word to use unless the wood is able to totally stop thermal energy from being conducted to the hand. ‘Minimise’ or ‘reduce’ is a more appropriate work to use.
Question 15
During a barbecue, why do we always cook food on top of the charcoal?
A
To increase the rate of heat transfer by conduction.
B
To increase the rate of heat transfer by convection
C
To increase the rate of heat transfer by radiation
D
To increase the rate of heat transfer by evaporation
Question 15 Explanation: 
Convection is a process whereby thermal energy is transferred from one point to another due to the difference in densities. Hot air rises. By placing the raw food directly above the charcoals, thermal energy from the charcoals reaches the raw food via convection from the hot air. If the raw food is placed at the side of the charcoals, thermal energy will only reach the raw food via radiation. This allows the raw food to receive thermal energy via convection and radiation.
Question 16
Which of the following about the vacuum flask are correct?
  1. The silvered surface reduces loss of thermal energy by radiation.
  2. The vacuum in the flask reduces loss of thermal energy by radiation.
  3. The stopper reduces loss of thermal energy by convection and evaporation.
A
1 and 2 only
B
1 and 3 only
C
2 and 3 only
D
1, 2 and 3
Question 16 Explanation: 
1. The silvered surface reduces loss of thermal energy by radiation. (Correct) Silvered surface is a bad absorber and radiator of heat. When we have silvered surface along the path of heat flow, radiation will be slowed down as silvered surface will reflect away the oncoming radiant heat and emit slowly the outgoing radiant heat. 2. The vacuum in the flask reduces loss of thermal energy by radiation. (Incorrect) Vacuum reduces loss of thermal energy via conduction and convection because conduction and convection need a medium for the flow of thermal energy. Radiation can take place in a vacuum. 3. The stopper reduces loss of thermal energy by convection and evaporation. (Correct) Stopper prevents the hot air (caused by convection and evaporation) from escaping out of the vacuum flask.
Question 17
Cooling fins are used in refrigerators, car radiator and many other cooling devices to dissipate thermal energy out of the system to the environment. Which of the following statements about the cooling fins are correct?
  1. The cooling fins are made of metal to ensure that thermal energy is being conducted quickly out to the environment.
  2. The cooling fins are thin for heat to be dissipated to the environment quickly via convection and radiation.
  3. Cooling fins are normally black to achieve higher rate of thermal energy radiation.
A
1 and 2 only
B
1 and 3 only
C
2 and 3 only
D
1, 2 and 3
Question 17 Explanation: 
1. The cooling fins are made of metal to ensure that thermal energy is being conducted quickly out to the environment. (Correct) 2. The cooling fins are thin for heat to be dissipated to the environment quickly via convection and radiation. (Correct) 3. Cooling fins are normally black to achieve higher rate of heat dissipation by radiation. (Correct)
Question 18
Petrol storage tanks are not painted black because
A
Black is a good conductor of heat.
B
Black is a bad conductor of heat.
C
Black is a good emitter of radiation.
D
Black is a good absorber of radiation.
Question 18 Explanation: 
Black is both a good absorber of radiation and a good emitter of radiation. For the case of the petrol storage tank, absorption of heat is not desired as ignition temperature may reach and explosion may occur.
Question 19
How does a polar bear keep itself warm?
  1. By salivating
  2. By having thick fur
  3. By having white fur
A
1 and 2 only
B
1 and 3 only
C
2 and 3 only
D
1, 2 and 3
Question 19 Explanation: 
1. Salivate (incorrect) Salivation is a way for animals to dissipate their body thermal energy to the environment by evaporation. 2. have thick fur (Correct) Fur traps air and air is a very poor conductor of heat. Having thick fur can reduce loss of thermal energy to the environment by conduction and indirectly loss of thermal energy by convection. 3. have white fur (Correct) White colour is a bad emitter of radiant heat. Rate of radiation to the environment for white fur is less than for black fur.
Question 20
Which of the following is false?
A
Dog drools (salivates) to allow heat loss by evaporation.
B
Elephant sprays water over its body to allow heat loss by evaporation.
C
Jack rabbit has enormous ears with many blood vessels to dissipate thermal energy
D
Camel has big humps to store water so that it can dissipate thermal energy by convection.
Question 20 Explanation: 
The big humps do not store water but fats and flesh of the camel. It is a food reserve to be absorbed by the camel as nutrition when food is scarce.
Question 21
Which of the following is false?
A
We wear white to keep ourselves warm during winter.
B
We wear white to keep ourselves cool during summer.
C
Aluminium foil are used to keep food warm.
D
Pipes are painted black to minimize transfer of thermal energy.
Question 21 Explanation: 
White and silver are bad emitter and had absorber of radiation. They minimize heat flow and thus maintain constant temperature. Black colour is a good emitter and good absorber of radiation. It maximizes heat flow. Human being (warm blooded) wants to maintain our bodies at a constant temperature so during winter we wear white to minimize loss of thermal energy by radiation and during summer we wear white to minimize gain of thermal energy from the environment. Aluminium foil being silver is normally used to wrap round over hot food to help to reduce loss of thermal energy by radiation. Black pipes are used to maximize heat absorption or heat emission by radiation.
Question 22
Which of the following will increase the rate of heat transfer?
  1. Increase the temperature difference
  2. Paint the surface black
  3. Increase the surface area
A
1 and 2 only
B
1 and 3 only
C
2 and 3 only
D
1, 2 and 3
Question 22 Explanation: 
A bigger temperature difference between two bodies creates a bigger driving force for the heat to flow between them. Black surface is a good absorber of radiation when the environment is hot and a good emitter of radiation when the environment is cold. A bigger surface area provides more opportunities between hot and cold media to interact and therefore enhance rate of heat flow.
Question 23
Which of the following is true about pots?
  1. Black pots are used for cooking because they increase the rate of cooking.
  2. Silver pots are used for keeping food warm because they decrease the rate of heat dissipation.
  3. Pots are made of clay to increase the rate of cooking.
A
1 and 2 only
B
1 and 3 only
C
2 and 3 only
D
1, 2 and 3
Question 23 Explanation: 
1. Black pots are used for cooking because they increase the rate of cooking. (Correct) Black colour is a good absorber of heat. It helps to increase the rate of cooking by increasing the heat absorption by radiation. 2. Silver pots are used for keeping food warm because they decrease the rate of heat dissipation. (Correct) Silver colour is a bad emitter of heat. It helps to decrease the rate of heat dissipation by radiation to the surrounding. 3. Pots are made of clay to increase the rate of cooking. (Incorrect) Clay does not contain much free electrons. Clay is a bad thermal conductor. Clay pots are used to keep the food in it warm and not to increase the rate of cooking.
Question 24
Which of the following can be done to increase the rate of cooking?
  1. Use a black pot instead of silver pot.
  2. Use a thick pot instead of thin pot
  3. Cover the pot with a lid.
A
1 and 2 only
B
1 and 3 only
C
2 and 3 only
D
1, 2 and 3
Question 24 Explanation: 
1. Use a black pot instead of silver pot (Correct) Black colour is a good absorber of thermal energy. It helps to increase the rate of cooking by increasing the heat absorption by radiation. 2. Use a thick pot instead of thin pot (Incorrect) A thick pot will require more time for the heat to travel. It will slow down the heating process. 3. Cover the pot with a lid. (Correct) The lid acts as a cover to prevent vapour (caused by evaporation) and hot air (caused by convection) to go out of the pot. It helps to trap thermal energy within the pot to increase the rate of cooking.
Question 25
Container A and container B are filled with equal amount of hot water and the temperature of the water in the containers is measured with a thermometer some time later. It is observed that container A has a much lower temperature than container B. What are the possible reason(s)?
  1. Container A is black and container B is silver.
  2. Container A has a lid and container B is not covered.
  3. Container A is made of steel and container B is made of clay.
A
1 and 2 only
B
1 and 3 only
C
2 and 3 only
D
1, 2 and 3
Question 25 Explanation: 
1. Container A is black and container B is silver. (Correct) Black colour is a good emitter of heat. It helps to increase the rate of heat emission out of the container by radiation. Container A loses heat faster and thus has a lower temperature. 2. Container A has a lid and container B is not covered. (Incorrect) The lid acts as a cover to prevent vapour (caused by evaporation) and hot air (caused by convection) to go out of the pot. Container A with a lid will trap more thermal energy inside the container and therefore should have a higher temperature. 3. Container A is made of steel and container B is made of clay. (Correct) Steel is a better conductor than clay. It will have a faster rate of thermal energy transfer out of the water than clay. Water with less thermal energy will have a lower temperature.
Question 26
Which of the following is true?
A
Sea breeze happens during night time when the sea is cooler than the area.
B
Sea breeze happens during day time when the land is cooler than the sea.
C
Land breeze happens during night time when the land is cooler than the sea.
D
Land breeze happens during day time when the sea is cooler than the land.
Question 26 Explanation: 
During day time, the temperature of the land is higher than the temperature of the sea (heat capacity of the land is lower than the heat capacity of the sea), hot air above the land rises rapidly and cool air above the sea will move towards the hot land to take up the empty space. This breeze that flows from sea to land is known as the sea breeze. During night time, the temperature of the sea is higher than the temperature of the land ((heat capacity of the land is lower than the heat capacity of the sea), hot air above the sea rises rapidly and cool air above the land will move towards the sea to take up the empty space. This breeze that flows from sea to land is known as the land breeze.
Question 27
The diagram shows a man standing under a shelter on a sunny day. Given that the man feels hot, which of the following shows the processes of how thermal energy from the sun reaches the man? 27
A
Radiation → Conduction → Radiation
B
Radiation → Conduction → Convection
C
Radiation → Convection → Radiation
D
Radiation → Convection → Convection
Question 27 Explanation: 
Radiation of thermal energy from the sun to the plastic. Conduction of thermal energy through the solid plastic shelter. Radiation of thermal energy from the underside of the shelter to the man.
Question 28
The diagram shows a man besides a campfire. How does thermal energy from the campfire reach the man? 28
A
By radiation
B
By convection
C
By radiation and convection
D
By conduction and convection
Question 28 Explanation: 
Air is a very bad conductor and therefore the transfer of thermal heat by conduction is negligible. Convection is caused by the density difference in the air. Since hot air rises, convection only transfers the thermal energy vertically upwards and not to the man who is at the side. Thermal energy is radiated in all the directions from the heat source. The man feels hot because he receives heat by radiation.
Question 29
The diagram shows a brick wall in between a man and a campfire. How does thermal energy from the campfire reach the man? 29
A
Radiation → Conduction → Radiation
B
Radiation → Conduction → Convection
C
Radiation → Convection → Radiation
D
Radiation → Convection → Convection
Question 29 Explanation: 
Radiation of thermal energy from the campfire to the brick wall. Conduct of thermal energy through the solid brick wall. Conduct of thermal energy through the solid brick wall. Radiation of thermal energy from the brick wall to the man.
Question 30
The diagram shows water being heated in a tin can. A thermometer hangs directly above it. How does thermal energy from the heat source reach the thermometer? 30
A
Radiation → Conduction → Radiation
B
Radiation → Conduction → Convection
C
Radiation → Convection → Radiation
D
Radiation → Convection → Convection
Question 30 Explanation: 
Thermal energy is transferred by radiation and convection from the heat source to the tin can. Thermal energy is transferred by conduction through the solid tin can. Thermal energy is transferred by radiation and convection from the tin can through the water. Thermal energy is transferred by radiation and convection from the surface of the water to the thermometer.
Question 31
Expanded polystyrene is often used to make containers for storing ice-cream because the trapped air reduces loss of thermal energy by
A
Radiation only.
B
Conduction only.
C
Conduction and convection.
D
Conduction, convection and radiation.
Question 31 Explanation: 
The vibration mechanism of conduction is not suitable for air because the distance between air molecules is very wide. Although air is a good medium for convection but trapped air doesn’t allow the heat to flow out to the atmosphere.
Question 32
Which of the following statements about the vacuum flask is incorrect?
A
Loss of thermal energy by radiation is minimized by keeping hot water in a double-walled container.
B
Loss of thermal energy is minimized by using a cork or plastic stopper to close up the neck of the glass container.
C
The vacuum in the double-walled glass container effectively prevents conduction and convection.
D
The walls of the glass container are silvered to reduce radiation.
Question 32 Explanation: 
The air gap between the two walls does not reduce the loss of thermal energy by radiation. It will reduce the loss of thermal energy if the two walls are painted silver.
Question 33
The chief mechanism for conduction in a typical metallic conductor involves
A
The diffusion of atoms in the conductor from the hot end to the cooler end.
B
Atoms near the hot end vibrating with big amplitudes about their fixed positions and transferring their energy to neighbouring atoms located in cooler regions by knocking against them.
C
The diffusion of free electrons from the hot end to the cooler end of the conductor carrying their energy along with them.
D
The atoms near the hot end sending out energy to atoms near the cooler end.
Question 33 Explanation: 
Conduction is the process whereby thermal energy is transferred by the vibration of molecules. In the case of good conductors, the diffusion of electrons from the hotter region to the cooler region has a much bigger effect in transfer of thermal energy than the conduction process.
Question 34
Some steamboat restaurants use paper pots for their customers to boil the food themselves. What is the reason for the paper not to catch fire when in contact with the flame?
  1. The paper is thin and therefore heat is conducted quickly to the water in the paper pot.
  2. Water has a boiling point lower than the burning temperature of the paper.
  3. The paper is thick enough to withstand the high temperature of the flame.
34
A
1 and 2 only
B
1 and 3 only
C
2 and 3 only
D
1, 2 and 3
Question 34 Explanation: 
A substance will only burn when three conditions are fulfilled. The presence of a fuel (thing to be burnt), oxygen and a high enough temperature (ignition temperature) for the fuel. The paper cannot burn because the thermal energy that goes to the paper is quickly taken away by the water and therefore the paper cannot reach its ignition temperature. The temperature of the paper cannot go higher than 100oC because the thin paper allows heat flow quickly from the flame to the water by conduction and the water’s boiling point is 100oC. All water must vaporize before the temperature can increase. The ignition temperature of paper is about 233oC.
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