Thermal Radiation (Edexcel GCSE Physics)

A copper can, painted black, contains boiling water at 100 °C.

The can is left to cool and a measurement of the water temperature is taken every 5 minutes.

Figure 3 shows the measurements.

Figure 3

i) Two points, shaded in the table, have not been plotted.

Plot these two points on the graph, in Figure 4.

Figure 4

[2]

ii) One of the points on the graph in Figure 4 is anomalous.

Circle the anomalous point.

[1]

iii) Draw the best fit curve on the graph in Figure 4.

[1]

iv) An identical can contains the same amount of boiling water.

This can has a shiny silver surface.

The measurements are repeated with this can and a new curve is drawn.

State how the cooling curve would be different from the curve in the graph in Figure 4.

[1]

Figure 5 is a graph showing the intensity–wavelength curves for two hot objects, L and M.

Figure 5

i) Estimate the wavelength where the intensity is at a maximum for each of the objects.

wavelength at maximum intensity for object L = ............. μ  

wavelength at maximum intensity for object M =.............. μm

[2]

ii) State, with  a reason, which object is the hotter object.

Object............................................

Reason...........................................

[1]

Figure 1 shows a Leslie cube which can be used to investigate how the surface of a hot object affects the radiation emitted. 

The cube has four different vertical surfaces, each painted a different colour.

When the cube is filled with boiling water the temperature of each surface is the same.

A radiation sensor can be used to measure the radiation emitted from each surface. 

Figure 1

Some results are shown below.  

Draw a line linking each surface colour with its correct meter reading. One has been done for you.

The temperature of each surface is the same, but the radiation sensor gives a different reading for each surface.

Explain why.

In a similar experiment, a student wants to investigate good and bad absorbers of thermal radiation.

They have the apparatus shown in Figure 2, a supply of cold water and a metre rule.

Figure 2

Explain how the student could use the apparatus they have available to carry out their investigation.

Describe the results they would expect to obtain. Draw a diagram of the set-up.

One application of these findings is in solar panel design.

A solar panel is mounted on the roof of a house.

Figure 3 shows a section through part of the solar panel. 

Figure 3

A pump makes water flow through the copper pipes. The water is heated by passing through the solar panel. 

Explain three features of the solar panel that maximise the final temperature of the water.

A student is performing an experiment to investigate how much infrared radiation is radiated by different coloured surfaces.

Four conical flasks are painted shiny grey, dull drey, black and white as shown in Figure 1.

Figure 1

They fill the four conical flasks with boiling water and record the subsequent temperature every 30 s.

State the dependent and independent variables in this experiment. 

State two control variables in this investigation. 

The results of the experiment are plotted in Figure 2 below. Each line represents the temperature loss of a different flask.

Figure 2

(i) State the letter of the curve with the lowest temperature change per second.

[1]

(ii) State the letter of the flask covered in the best conductor. 

[1]

(i) Draw four lines between the labels from Figure 2 and the different flask colours. 

[4] 

(ii)   Suggest why the temperature of flask D does not drop below 23 °C.

[1]

A student constructs a device for absorbing thermal energy from the Sun as shown in Figure 1.

Figure 1

The student places the white plastic pipe in sunlight. The cold water flows slowly from Tank A to Tank B. Energy from the Sun heats the water in the pipe.

Figure 2 shows the temperatures in Tank A and Tank B.

 Figure 2

Determine the rise in temperature of the water.

 temperature rise = .................................................... °C

The student wants to increase the thermal energy absorbed by the water in the pipe.

Suggest three improvements he can make to increase the thermal energy absorbed.

Describe how the thermal energy is transferred from the Sun to the water inside the pipe.

The rate of absorption and emission of radiation on Earth contributes to the Greenhouse Effect.

This is the natural process that warms the Earth's surface from the Sun.

Explain how the Greenhouse Effect occurs.

A student investigates the thermal energy lost from two metal cans, A and B. The cans are identical apart from their outside colour.

The student pours the same volume of hot water into each can and seals each can. The student records the temperature of the water in each can at regular time intervals for a period of 35 minutes.

The equipment is shown in Figure 1.

Figure 1

The results from the investigation are shown in Figure 2.

Figure 2

For Can A, use Figure 2 to determine the drop in temperature of the water 

(i) in the first five minutes

[1]

(ii) in the last five minutes

[1]

Explain why the water cools at a greater rate during the first five minutes of the experiment, compared with the last five minutes.

The outside of one can is dull black and the outside of the other is shiny white. 

State the colour of can Y.  

Explain your answer.

State two safety precautions that should be taken during this experiment.

i) Figure 4 shows two light rays hitting a glass lens.

On Figure 4, draw the two light rays after they leave this lens.

Figure 4

[1]

ii) Figure 5 shows two light rays hitting a different glass lens.

On Figure 5, draw the two light rays after they leave this lens.

Figure 5

[1]

iii) A lens has a focal length of 25 cm.

Calculate the power of the lens.

Use the equation

power of the lens = .......................... dioptres[2]

Figure 6 shows two solid metal balls, P and Q.

Figure 6

P and Q are made from the same metal and have the same radius.

P is painted black and Q is painted white.

Each ball is heated to a different temperature.

The balls then cool in the same room.

The graph in Figure 7 shows how the temperature of each ball changes with time.

Figure 7

i) Use the graph in Figure 7 to determine the time when P and Q were at the same temperature.

Show your working on the graph.

time = ........................................... minutes[2]

ii) Which of these temperatures is most likely to be room temperature, as shown by the graph in Figure 7?

[1]

iii) Explain why the curve for P is different from the curve of Q. Use information from Figure 6 and Figure 7 to help your answer.

[2]

Equal volumes of hot water are added to two cans.

The cans are identical apart from their surfaces.

One can has a black surface and the other can has a silver surface.

The cans are left to cool and their temperatures are monitored. The graph in Figure 6 shows the results.

Figure 6

Explain, using evidence from the graph, which curve is for the black can and which curve is for the silver can.

Figure 7 shows some apparatus. 

Figure 7

Describe an investigation to find out how the nature of a surface affects the amount of thermal energy absorbed by the surface.

You should use the apparatus in Figure 7 and any additional items you choose.

Each can in Figure 7 has a bung in the top with a hole in it.

You may use a diagram if it helps your answer.  

Figure 8 shows a section of the electromagnetic spectrum. 

Figure 8

i) State one type of electromagnetic radiation that has a higher frequency than ultraviolet. 

[1]

ii) One star is blue and another star is red.

Explain why an astronomer expects the blue star to be hotter than the red star.

[2]