I've got the question below in a homework task and i need some help:

The unknown resistance R of a resistor can be measured by comparing with a 100Ω standard. A potentiometer slide-wire, which consists of a bare wire with constant resistivity, so that contact can be made at any point along its length, is used to find two balance points where the current through the ammeter is zero, when A is connected to B or C.

When A is connected to B, the balance point was found to be when l=400mm.

When A is connected to C, the balance point was found to be when l=588mm.

Any thoughts?

The unknown resistance R of a resistor can be measured by comparing with a 100Ω standard. A potentiometer slide-wire, which consists of a bare wire with constant resistivity, so that contact can be made at any point along its length, is used to find two balance points where the current through the ammeter is zero, when A is connected to B or C.

When A is connected to B, the balance point was found to be when l=400mm.

When A is connected to C, the balance point was found to be when l=588mm.

Any thoughts?

(edited 5 months ago)

It would help to see working, but basically the current through the ammeter = 0 when the pd across it is 0.

You know resistance = constant * length

So set up 2 equations where the pd dropped in the top loop = pd dropped in the bottom loop, with one equation for each different length.

Then cancel stuff and solve

You know resistance = constant * length

So set up 2 equations where the pd dropped in the top loop = pd dropped in the bottom loop, with one equation for each different length.

Then cancel stuff and solve

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