Heat transfer by radiation — KCSE Physics

KCSE Physics · 129 practice questions · 8 syllabus objectives

41 easy42 medium46 hard

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Explain the greenhouse effect, solar energy applications and the role of surface colour in cooling and heating

State that thermal radiation is an electromagnetic wave that travels through a vacuum

Compare the emission and absorption of radiation by surfaces of different colour and texture (dull/shiny, black/white)

Describe the greenhouse effect and explain how radiation is used in solar panels and vacuum flasks

Define thermal radiation and state factors affecting emission and absorption of radiation

Describe experiments using Leslie’s cube and cans to compare emission and absorption by different surfaces

Describe the vacuum flask and explain how it minimises heat loss by conduction, convection and radiation

Heat transfer by radiation

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easySHORT ANSWER2 marks

Name two ways in which solar panels utilise the principles of radiation to generate energy. (2 marks)

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Part (a) — 2 marks

Solar panels absorb thermal radiation from the sun to heat a fluid (1 mk)

Solar panels convert electromagnetic radiation into electrical energy through photovoltaic cells (1 mk)

easySHORT ANSWER3 marks

State three reasons why a black surface is a better emitter of radiation than a shiny surface. (3 marks)

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Part (a) — 3 marks

Black surfaces absorb more thermal radiation (1 mk)

Dull surfaces have lower reflectivity, allowing more radiation emission (1 mk)

Black surfaces are generally better at converting thermal energy into radiation (1 mk)

easySHORT ANSWER2 marks

State how thermal radiation differs from conduction and convection in terms of the medium required for heat transfer. (2 marks)

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Part (a) — 2 marks

Thermal radiation does not require a medium and can travel through a vacuum (1 mk)

Conduction and convection require a material medium to transfer heat (1 mk)

Name two everyday examples of thermal radiation and explain their significance. (4 marks)

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