Heat transfer by convection — KCSE Physics

KCSE Physics · 123 practice questions · 8 syllabus objectives

39 easy44 medium40 hard

What You'll Learn

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

Describe applications of convection in heating systems, ventilation and rainfall formation

Explain convection in fluids in terms of density differences due to temperature changes

Describe convection currents in the atmosphere (sea breeze, land breeze) and in heating systems

Explain why convection cannot occur in solids or in a vacuum

Define convection and explain how convection currents are set up in fluids

Describe experiments to demonstrate convection in liquids and gases

Explain the formation of land and sea breezes using convection

Heat transfer by convection

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easySHORT ANSWER3 marks

State how convection leads to the formation of land breezes during the night. (3 marks)

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Part (a) — 3 marks

Land cools down faster than water at night, causing the air above the land to become cooler and denser (1 mk)

The cooler, denser air over the land sinks and creates an area of high pressure (1 mk)

The warmer, less dense air over the sea rises, creating an area of low pressure, resulting in a breeze blowing from land to sea (1 mk)

easySHORT ANSWER3 marks

State how you would demonstrate convection currents in a beaker of water using food colouring. (3 marks)

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Part (a) — 3 marks

Heat the bottom of the beaker to warm the water (1 mk)

Add a few drops of food colouring at the surface of the water (1 mk)

Observe the movement of the coloured water as it mixes and shows the convection currents (1 mk)

easySHORT ANSWER2 marks

Name two factors that contribute to the formation of sea breezes during the day. (2 marks)

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Part (a) — 2 marks

Land heats up faster than water, causing the air above it to rise (1 mk)

Cooler, denser air from the sea moves in to replace the rising warm air (1 mk)

Explain how convection currents are formed in a heated fluid and describe the role of density differences in this process. (4 marks)

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