6.10 Required practical: infrared radiation from surfaces
9 exam questions worth 19 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Which surface emits the most infrared radiation at the same temperature?
Choose one answer.
Correct Not quite: the answer is Matt black
Mark scheme
C: Matt black
Model answer
Matt black (C).
State the independent variable and the dependent variable in this investigation.
Mark scheme
independent: type / colour / texture of the surface (1); dependent: reading on the infrared detector / intensity of infrared radiation (1)
Model answer
The independent variable is the type of surface. The dependent variable is the reading on the infrared detector.
Give two control variables in this investigation.
Mark scheme
any two from: temperature of the water (1); distance of the detector from the surface (1); area of the face (1); the same detector (1)
Model answer
The temperature of the water and the distance from the detector to the surface.
Explain why the student should measure the infrared radiation from each face of the cube as quickly as possible.
Mark scheme
the water in the cube cools down (1); so the temperature of the surfaces falls, which would affect the readings / make it unfair (1)
Model answer
The water cools, so the cube's temperature falls, which would change the amount of infrared emitted and make the test unfair.
A student takes the readings in the order matt black, matt white, dull metal, shiny metal and repeats them in the reverse order. Explain why.
Mark scheme
the cube cools down during the experiment (1); doing it in a different order, and finding a mean, removes the effect of cooling on a particular surface (1)
Model answer
The cube cools as the experiment goes on, so doing the readings in a different order, and finding the mean, means that the cooling does not affect one surface more than the others.
Describe the pattern shown in the results and state what it shows about matt black surfaces.
Mark scheme
matt black gives the highest reading and shiny metal the lowest (1); matt black surfaces are the best emitters of infrared radiation (1)
Model answer
Matt black gives the highest reading and shiny metal the lowest, so matt black is the best emitter of infrared radiation.
Explain why radiators in a central heating system are usually painted matt, rather than shiny.
Mark scheme
matt surfaces are better emitters of infrared radiation (1); so more energy is transferred to the room (1)
Model answer
A matt surface is a better emitter of infrared radiation, so a radiator transfers more energy to the room.
Describe an experiment to show that a matt black surface is a better absorber of infrared radiation than a shiny surface.
Mark scheme
place a matt black plate and a shiny plate the same distance from a radiant heater (1); with a thermometer / sensor on the back of each plate (1); measure the temperature rise of each after the same time (1); the matt black plate heats up more quickly / by more (1)
Model answer
Put a matt black plate and a shiny plate at the same distance from a heater, each with a thermometer on the back. Measure how much each one's temperature rises in the same time. The matt black plate will warm up faster.
State two safety precautions needed when using a Leslie cube.
Mark scheme
use a heat-resistant mat / place on a stable surface (1); do not move the cube when it is full of hot water / be careful with boiling water (1)
Model answer
Use the cube on a heat-resistant mat, and take care when pouring in boiling water to avoid scalds.
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