# Finding terminal voltage without voltmeter

<< Mentor Note -- OP has been warned about not showing any effort toward a solution >>

1.
How can I find the terminal voltage across a 6v power supply, without using a voltmeter. The problem is the only equipment listed on the practical is an ammeter and a resistor with unspecified resistance...

V=IR
V=emf-Ir

## The Attempt at a Solution

Not a clue

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Stephen Tashi
What does the resistor look like? No color code? Any way to use only part of it in a circuit?

No idea, I have only been provided with a list of equipment, but the practical is in about half an hour...

This is the practical I'm doing

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I'm only confused on the first point, seeing as no internal resistance or resistance of any resistor has been stated... It simply asks to draw a circuit set-up to find the terminal voltage across the power supply

Stephen Tashi
Assuming the protective resistor isn't color coded, the only idea that comes to my mind is to incorporate varying lengths of the wire in the circuit.

R = unknown resistance of protective resistor
Rw = unknown resistance of the wire
V = unknown voltage

Using the circuit in Fig. 1.1, assume incorporating 1/3 of the wire in the circuit puts a resisance Rw/3 in the circuit, etc
Make measurements to establish simultaneous equations

For example:

V = I1 R + I1 Rw
V = I2 R + I2 Rw/2
V = I3 R + I3 Rw/3

Gives 3 equations with currents I1, I2, I3 known by measurement to solve for unknowns V, R, Rw

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Stephen Tashi