Transfer Of Thermal Energy - Radiation
Online Quiz - Radiation
- 1.
Which types of surface are the best absorbers and the best emitters of infra‑red radiation?
- A.
Best absorber - black and dull Best emitter - black and dull
- B.
Best absorber - black and dull Best emitter - white and shiny
- C.
Best absorber - black and shiny Best emitter - white and dull
- D.
Best absorber - white and dull Best emitter - black and shiny
Correct Answer
A. Best absorber - black and dull Best emitter - black and dullExplanation
Black and dull surfaces are the best absorbers and emitters of infra-red radiation because they have a higher ability to absorb and emit radiation compared to other surfaces. Black surfaces absorb more radiation because they have a higher absorption coefficient, meaning they can absorb a larger amount of radiation that falls on them. Dull surfaces, on the other hand, have a higher emissivity, which allows them to emit a larger amount of radiation. This combination of high absorption and high emission makes black and dull surfaces the best absorbers and emitters of infra-red radiation.Rate this question:
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- 2.
A small piece of aluminium is placed in your hand. After a short while, your hand feels warm. Explain why this happens.
- A.
Aluminium reflects the thermal energy radiated by the hand.
- B.
Aluminium absorbs thermal energy radiated from the surroundings.
- C.
Aluminium radiates thermal energy well.
- D.
Aluminium is a good absorber of radiation.
Correct Answer
A. Aluminium reflects the thermal energy radiated by the hand.Explanation
Aluminium is a good reflector of thermal energy. When the hand comes in contact with the aluminium, the thermal energy radiated by the hand is reflected back towards the hand instead of being absorbed by the aluminium. This reflection of thermal energy causes the hand to feel warm.Rate this question:
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- 3.
In the following set-up, equal volumes of hot water were poured into the containers and the temperatures of both containers and contents were the same. After an hour, the temperature of container P was found to be lower than that of container Q. This shows that P is a better ____ of heat than Q.
- A.
Conductor
- B.
Absorber
- C.
Radiator
- D.
Conductor and absorber
Correct Answer
C. RadiatorExplanation
Thermal energy needs to be radiated out of the container into the surroundings. For P to be at a lower temperature, it has to be a better radiator.Rate this question:
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- 4.
A small cork is fixed with wax to a metal plate. An electric heater is placed close to the plate. After a time, the wax melts and the cork drops off. How does thermal energy reach the wax?
- A.
By conduction only
- B.
By conduction and convection
- C.
By radiation and conduction
- D.
By radiation and convection
Correct Answer
C. By radiation and conductionExplanation
Thermal radiation radiates from the electric heater and conducts through the air. Convection cannot occur because the metal plate is not located above the heater.Rate this question:
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- 5.
A copper plate is heated to 100oC and then allowed to cool. It cools by emitting __________.
- A.
Electrons
- B.
Gamma radiation
- C.
Infra-red radiation
- D.
Ultraviolet radiation
Correct Answer
C. Infra-red radiationExplanation
When a copper plate is heated to 100oC and then allowed to cool, it cools by emitting infra-red radiation. Infra-red radiation is a form of electromagnetic radiation with longer wavelengths than visible light. As the copper plate cools, the atoms and molecules in the plate lose energy and emit this radiation. This radiation carries away the excess heat energy from the plate, causing it to cool down.Rate this question:
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- 6.
A vacuum will prevent heat transfer by ___________.
- A.
Convection only
- B.
Conduction and convection only
- C.
Radiation only
- D.
Conduction, convection and radiation
Correct Answer(s)
B. Conduction and convection only
D. Conduction, convection and radiationExplanation
A vacuum will prevent heat transfer by conduction and convection only because there are no particles or molecules present in a vacuum to transfer heat through direct contact or through the movement of fluids. However, a vacuum does not prevent heat transfer by radiation, as radiation can occur through the emission and absorption of electromagnetic waves, which do not require a medium to travel through.Rate this question:
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- 7.
A solar heater uses energy from the Sun to heat water. The panels of the heater are painted black. Why is this?
- A.
To improve absorption of infra-red radiation
- B.
To improve emission of infra-red radiation
- C.
To improve the conducting properties of the panel
- D.
To reduce convection currents
Correct Answer
A. To improve absorption of infra-red radiationExplanation
The panels of a solar heater are painted black to improve absorption of infra-red radiation. Black surfaces have a higher absorption rate for radiation compared to other colors, allowing the panels to absorb more of the Sun's energy and convert it into heat. This helps to maximize the efficiency of the solar heater in converting sunlight into thermal energy for heating water.Rate this question:
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- 8.
Which of the following will be the best absorber of infra-red radiation?
- A.
Dark animal fur
- B.
Shiny metal tray
- C.
White plastic bag
- D.
Writing paper
Correct Answer
A. Dark animal furExplanation
Black coloured objects are better absorbers of thermal energy.Rate this question:
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- 9.
When metal hot-water pipes are used to heat air in a room, how is most of the energy transferred through the metal and through the air?
- A.
Through metal - conduction through air - convection
- B.
Through metal - conduction through air - radiation
- C.
Through metal - convection through air - convection
- D.
Through metal - convection through air - radiation
Correct Answer
B. Through metal - conduction through air - radiationExplanation
Radiation is a more efficient method of heat transfer than convection.Rate this question:
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- 10.
The thermal energy from a campfire during a scout camp reaches the scouts’ faces mainly by __________.
- A.
Radiation only
- B.
Radiation and conduction
- C.
Convection only
- D.
Radiation and convection
Correct Answer
A. Radiation onlyExplanation
Air is a bad conductor of thermal energy. So most of the thermal energy will reach the faces by radiationRate this question:
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