# Finding terminal voltage without voltmeter

1. Jan 22, 2015

### learnings_sweet

<< 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...

2. Relevant equations
V=IR
V=emf-Ir

3. The attempt at a solution
Not a clue

Last edited by a moderator: Jan 22, 2015
2. Jan 22, 2015

### Stephen Tashi

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

3. Jan 22, 2015

### learnings_sweet

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

4. Jan 22, 2015

### learnings_sweet

This is the practical I'm doing

Last edited by a moderator: May 7, 2017
5. Jan 22, 2015

### learnings_sweet

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

6. Jan 22, 2015

### 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

Last edited: Jan 22, 2015
7. Jan 22, 2015

### Stephen Tashi

Good luck. It's 4:30 AM here and I must go to bed.