Heat radiation plenary MCQs

A small cork is attached to a metal plate with wax. An electric heater is placed close to the plate. After a time, the wax melts and the cork drops off. How does heat reach the cork?

• A by conduction only.

• B by convection only

• C by conduction and convection

• D by conduction and radiation.

The main reason for the vacuum is to reduce heat transfer due to

• A conduction only.

• B convection only.

• C radiation only.

• D conduction and convection.

Which types of surfaces are the best absorber and the best emitter of infra-red radiation?

• A best absorber: black and dull;

  best emitter: black and dull

• B best absorber: black and shiny;

  best emitter: white and dull

• C best absorber: white and dull;

  best emitter: black and shiny

• D best absorber: white and shiny;

  best emitter: white and shiny.

The diagram shows a vacuum flask and an enlarged view of a section through the flask wall.

The main reason for the silvering is to reduce heat transfer by

• A conduction.

• B radiation only.

• C conduction and convection.

• D convection and radiation.

A slice of bread is placed under a red-hot electric grill to make toast. How does the heat energy reach the bread?

• A by conduction

• B by conduction and convection

• C by convection and radiation

• D by radiation only

The tubes inside solar heating panels allow the Sun’s radiation to warm water. These tubes are painted black because

• A dark surfaces absorb radiation well.

• B dark surfaces conduct heat well.

• C dark surfaces emit radiation well.

• D dark surfaces reflect radiation well.

Which surface is the best emitter of heat radiation.

• A dull black

• B dull white

• C shiny black

• D shiny white.

A copper plate is heated in air to 100⁰C and then allowed to cool. It cools by emitting.

• A beta-particles
  

• B gamma-rays

• C infra-red radiation

• D ultraviolet radiation

Two identical metal plates are painted, one matt white and the other matt black. These are placed at equal distances from a radiant heater as shown. The heater is turned on for five minutes. Which metal plate absorbs more energy and which plate emits more energy in this time?

• A absorbs more: black, emits more: black

• B absorbs more: black, emits more: white

• C absorbs more: white, emits more: black

• D absorbs more: white, emits more: white

A long copper pipe is attached to a metal sheet, as shown below. Cold water is passed through the pipe. When the apparatus is placed in sunlight, the water is warmed.

(a) What colour should the apparatus be painted to make the water as hot as possible? [1]

(b) Explain your answer to (a) [1]