May 29, 2012

Finding the Resistance of a Voltmeter

Today, I am sharing a method of finding the resistance of a voltmeter by a drawing graph between RH & 1/V. I performed this experiment in university lab.

The purpose of sharing this experiment process is to help fellow students for preparation of their Physics lab manuals.

Keep reading this post for circuit diagrams and full range of all the values and tables. This experiment was performed in the Campus Physics lab.

Experiment # 4

Finding the resistance of voltmeter by drawing graph between RH & 1/V

Apparatus: DC voltmeter of unknown resistance, Power Supply, Resistance Box, Key, Connecting Wires.
Circuit Diagram: Voltmeter, Battery, Key, High Resistance Box

  1. First of all I connect power supply, voltmeter, high resistance box and key in series as shown in figure.
  2. The power supply has greater e.m.f than range of voltmeter.
  3. I connected the circuit to the DC power supply by closing the key K.
  4. I adjusted the resistance (R) of HRB in such a way that there were deflections on the scale of voltmeter.
  5. To get multiple values I changed the resistance of H.R.B several times.
  6. Find out I/V reading and then plot graph between resistance ‘R’ of resistance box and I/V by taking ‘R’ on x-axis and I/v on y-axis.
  7. Extend this line backwards. It will intersect x-axis on –ive side.
Least count of voltmeter = Lc = Vv/Nv

Vv = Maximum voltage on scale of voltmeter.

Nv = Total number of division on scale of voltmeter.

Observations and Calculations:

This is all for finding the resistance of a voltmeter.

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