Finding terminal voltage without voltmeter

  • #1
<< 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...


Homework Equations


V=IR
V=emf-Ir


The Attempt at a Solution


Not a clue
 
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Answers and Replies

  • #2
Stephen Tashi
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What does the resistor look like? No color code? Any way to use only part of it in a circuit?
 
  • #3
No idea, I have only been provided with a list of equipment, but the practical is in about half an hour...
 
  • #4
http://www.ocr.org.uk/Images/67766-unit-g483-practical-skills-in-physics-1-quantitative-task-specimen.pdf [Broken]
This is the practical I'm doing
 
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  • #5
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
Stephen Tashi
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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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  • #7
Stephen Tashi
Science Advisor
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Good luck. It's 4:30 AM here and I must go to bed.
 

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