GCE (A-level) Physics E16 Internal Resistance 2 of 4

[Steve4Physics]

Hi sedani2

I presume you mean “would the terminal pd always be 0 when there’s a short circuit?”

It depends how accurate you are trying to be.

Providing the resistance of whatever is causing the short-circuit is zero, then the terminal pd will be zero.

But in real life, pieces of (even thick) wire still have some resistance, and there will be some contact-resistance where the short-circuiting wire connects to the terminals. So in practice, the answer will be: not quite zero but very close.

[sedani2]

would it always be 0? when theres a short circuit?

[Steve4Physics]

If the internal resistance is changed from 0.1Ω to 0.75Ω and if (and this is a big IF) the current remained 2A, then you would correct – the ‘lost volts’ would equal the emf and the voltage (terminal pd) would be zero.

This could only happen if the cell is short-circuited – joining one side of the cell to another with thick wire (not recommended!).

[D1Z3AZ3D]

One question sir, at 4:55, in that diagram, you showed that the voltage that has been lost can be determined by currentxresistance= 0.2v. Does that mean if the resistance in that exact diagram was 0.75ohms, there would be no power coming out of the cell? (as 2x0.75= 1.5, and voltage remaining = 1.5-1.5= 0)