The Student Room Group

Quick multiple choice question

A variable resistor is connected across the terminals of a power supply of constant e.m.f. and
internal resistance r.

The resistance of the variable resistor is changed from zero to its maximum value.
Which of the following statements is/are correct?
1 The current in the circuit decreases.
2 The p.d. across the internal resistance decreases.
3 A graph plotted of terminal p.d. against current has a negative gradient.
A Only 1
B Only 1 and 2
C Only 1 and 3
D 1, 2 and 3

Why is statement 2 correct?
The internal resistance is a fixed value resistance with the full current provided by the power supply going through it.

So it follows from the first point, as the current coming out of the power supply gets reduced the PD across the internal resistor must also get reduced because V=IR
Original post by Joinedup
The internal resistance is a fixed value resistance with the full current provided by the power supply going through it.
So it follows from the first point, as the current coming out of the power supply gets reduced the PD across the internal resistor must also get reduced because V=IR

Thanks

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