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AS Physics question

There is an electrical circuit that includes a flat circular coil. A small compass is placed close to the coil along its axis. When the switch is closed, the compass needle deflects so that it points in the direction North, away from the coil.

Okay, there is a graph with shows how the current varies with time t after the switch is closed.

It starts at 6A and decreases to 2A at 1.5 seconds and remains constant.

Explain why the current changes. 4 marks.
Reply 1
Avatar for corkskrew
corkskrew
2
Current flows through the circuit.
Temp increases.
Kinetic energy of metal atoms in the wire increases.
Ability of electrons to flow freely through the wire decreases - fewer paths available
This is an increase in resistance.
V=IR........potential difference the same, resistance increases, current therefore decreases.
Reply 2
Avatar for Dimez
Dimez
2
Widowmaker
There is an electrical circuit that includes a flat circular coil. A small compass is placed close to the coil along its axis. When the switch is closed, the compass needle deflects so that it points in the direction North, away from the coil.

Okay, there is a graph with shows how the current varies with time t after the switch is closed.

It starts at 6A and decreases to 2A at 1.5 seconds and remains constant.

Explain why the current changes. 4 marks.


Initially the current decreases since the temperature of the wires in the circuit is increasing, causing the positive metal ions to vibrate more vigorously hence impeding the flow of the conduction electrons, causing an increase in resistance thus current drops to 2A. The current stays constant from then on since there are no more temperature fluctuations and the resistance stays the same, therefor current also stays constant.
corkskrew
Current flows through the circuit.
Temp increases.
Kinetic energy of metal atoms in the wire increases.
Ability of electrons to flow freely through the wire decreases - fewer paths available
This is an increase in resistance.
V=IR........potential difference the same, resistance increases, current therefore decreases.

oh is it really as simple as that? Thankyou.
Reply 4
Avatar for corkskrew
corkskrew
2
Widowmaker
oh is it really as simple as that?


Yeah - an A level question based on a key stage 3 equation. Who'd have thought?
Reply 5
Avatar for john !!
john !!
14
corkskrew
Yeah - an A level question based on a key stage 3 equation. Who'd have thought?
Lol well it is quite a widely used equation.

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