Energy Transfers
4 marks · NormalA cyclist uses an electric light powered by a small dynamo attached to the bicycle wheel. When cycling, the dynamo transfers energy from the movement of the wheel to other forms.
Name the main useful energy output from the dynamo.
State one form of energy that is wasted during the operation of the dynamo.
Describe, using the idea of energy stores, how energy is transferred from the cyclist’s body to the moving bicycle and eventually produces light.
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) Light (energy/light energy)
(b) Heat (thermal energy) or sound (energy)
(c) Chemical energy in muscles is transferred to kinetic energy (movement) in the cyclist and the bicycle. The kinetic energy is transferred to the dynamo, which converts it to electrical energy. The lamp then changes electrical energy into light energy (and some heat).
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Marking points
B1 (a) · 1 mark · States light energy as the useful output from the dynamo.
B1 (b) · 1 mark · Names heat or sound as a wasted energy form.
M1 (c) · 1 mark · Describes transfer from chemical energy (muscles) to kinetic energy (movement of bike/cyclist).
M1 (c) · 1 mark · Describes transfer from kinetic energy to electrical energy in the dynamo, then to light energy by lamp.
Worked solution
(a) The useful energy output is light energy.
(b) Wasted energy forms include heat and sound.
(c) Chemical energy in the cyclist's muscles is transferred to kinetic energy as they pedal. This kinetic energy turns the bicycle wheel, driving the dynamo, which converts kinetic energy into electrical energy. The lamp then converts electrical energy into light (useful) and heat (wasted).