Download Materials and equipment required

1 Energy
Teacher and technician notes
Energy transfer by heating process
Objectives
The intentions of this investigation are:
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to present convection in a different context from that seen at Key Stage 3.
•
to provide an opportunity for students to explain convection in their own words.
Safety
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The current through the immersion heaters should not exceed 1 A. This can be adjusted using
the variable resistor in the circuit.
•
Students’ circuits should be checked before they begin heating.
Materials and equipment required
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Two thermometers (0–110 °C)
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Retort stand and clamp
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Boiling tube
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Stop-clock
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Power pack
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Small immersion heater (this can be made by coiling thick nichrome wire around a pencil)
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Electrical leads
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Variable resistor (see safety note)
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Ammeter
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Crocodile clips
© Hodder & Stoughton Limited 2016
1 Energy
Teacher and technician notes
Answers
1 a) When the immersion heater is at the bottom, the water at the top still gets hotter, although
less quickly. The water at the bottom may not get hotter during the short heating time but, if
it does, it will heat up only slightly.
b) When the immersion heater is at the top, the water at the top will heat up. The water at the
bottom will remain cool.
2 When heated, water at the bottom of the tube expands and becomes less dense. The less dense
water rises and cooler, denser water at the top sinks. So the hot water is always found at the top
and the cooler water at the bottom.
3 When the water is heated at the top, hot less dense water is already at the top so it does not mix
with the water below. The water at the bottom therefore stays cool.
4 The highest temperature is produced when the immersion heater is near the top of the water.
5 The bottom position of the immersion heater will give most hot water if left for long enough
because the water is constantly mixing.
6 a) The bottom immersion heater will be needed for a bath so that plenty of hot water is
available.
b) The top heater will heat enough water quickly for washing up.
© Hodder & Stoughton Limited 2016