ELECTRICAL POWER
3 marks · NormalA student connects a thin filament lamp and a mains kettle in parallel to a 230 V supply. Both use the heating effect of current.
Explain why the lamp glows but the kettle does not.
State one use of the heating effect of electric current, other than in a lamp or a kettle.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) The lamp's filament is much thinner and heats up to white-hot easily when current passes through it, causing it to glow. The kettle's heating element is not designed to glow and does not reach such high temperatures; it mainly gets hot but not bright like a lamp. · must show mention filament thinner and heats more, reference to filament glowing white hot
(b) An electric cooker / toaster / hairdryer / washing machine / iron / electric fire. · must show valid appliance using heating effect
Also accept: both glow and heat if both switched on
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Explain the lamp's filament heats up quickly and glows brightly due to being thin.
M2 (a) · 1 mark · State the kettle's heating element is not designed to glow white hot (gets hot, not bright).
B1 (b) · 1 mark · Name another appliance that uses the heating effect appropriately.
Worked solution
a) The lamp contains a thin filament with high resistance that heats up quickly and glows white-hot when electrical current passes through. The kettle's heating element is much thicker and designed to heat water but does not reach a high enough temperature to glow; it mainly just gets hot but does not emit light.
b) Example: electric cooker, iron, toaster, hairdryer, washing machine, electric fire.