Thermal Radiation Practice Questions

An iron poker is lying on a table in a room at $20\;^{\circ}\text{C}$.

Which statement about the poker is correct? Put a cross ($\boxtimes$) in the box next to your answer.

A It does not emit any thermal radiation.

B It emits thermal radiation mainly as visible light.

C It emits thermal radiation mainly as infrared.

D It absorbs thermal radiation but does not emit any.

The poker is then put into a fire. After a few minutes it glows red.

Describe two changes to the radiation emitted by the poker as its temperature increases.

Give two variables that the student must keep the same so that the investigation is a fair test.

Describe how the student should use the apparatus to find out which surface is the better absorber of thermal radiation.

Describe two ways in which the curve for the block at $1800\;\text{K}$ differs from the curve for the block at $1200\;\text{K}$.

A lamp filament glows a dull red when its temperature is about $1000\;\text{K}$, but gives out white light when its temperature is about $3000\;\text{K}$.

Explain this difference, using ideas about the radiation emitted by hot bodies.

Explain what must be true about this radiation for the average surface temperature of the Earth to stay constant.

The concentration of greenhouse gases in the Earth's atmosphere is increasing.

Explain how this leads to an increase in the average temperature of the Earth's surface.

As the Earth warms, ice sheets melt and are replaced by darker ocean and land.

Explain how this affects the temperature of the Earth.

Compare the cooling of the two cans during the $300\;\text{s}$. Use data from the table in your answer.

Calculate the mean rate of cooling of the matt black can over the $300\;\text{s}$. State the unit.

mean rate of cooling = .............................. unit ..............................

The rate of cooling of each can decreases as time goes on.

Explain why.

State and explain what happens to the temperature of the probe at this point in its journey.

The probe stays the same distance from the Sun for several days. Its temperature eventually becomes constant.

Explain why.

The probe then moves away from the Sun. The average power it absorbs falls to $300\;\text{W}$.

Explain what happens to the temperature of the probe from this point onwards.

Explain why the detector must be placed the same distance $d$ from each face.

One of the results for the shiny silver surface is anomalous.

Identify the anomalous result and calculate the mean reading for the shiny silver surface, ignoring the anomaly.

mean reading = .............................. mV

The student concludes: "Black surfaces are the only good emitters of thermal radiation."

Evaluate this conclusion and suggest one improvement to the method.