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Aim:
To convert the given galvanometer (of known resistance and figure of merit) into a voltmeter of desired range and to verify the same.
Apparatus Required:
A galvanometer, a voltmeter 0-3V, battery, 2 resistance box (10,000 ohms and 200 ohms), 2 one way keys, a rheostat, connecting wires and sandpaper.
Theory:
A galvanometer is an ideal device that is capable of detecting even the weakest electric currents in an electric circuit. It features a coil suspended or pivoted between concave pole faces of a strong laminated horseshoe magnet. The galvanometer shows the deflection when an electric current is passed through the coil. The deflection is directly proportional to the current passed. A voltmeter is an instrument used for estimating the electrical potential difference between 2 points in an electric circuit.
Series resistance required for conversion
V-range of conversion
Diagram
Procedure
- Connect the resistance box in series combination with the galvanometer and take the plugs of resistance R.
- A and B are the fixed terminals and C is the variable terminal of the rheostat.
- Now the galvanometer functions as a voltmeter of range V Volts.
- Take out the plugs of calculated resistance R from the resistance box.
- By using a key, adjust the movable contact of the rheostat such that the deflection of the galvanometer becomes maximum.
- Note both the readings of the galvanometer and voltmeter.
- Convert the readings of the galvanometer into volts.
- Find the difference in the reading. This difference between voltmeter reading and galvanometer reading gives the error.
- By moving the variable contact of rheostat, take 5 readings covering the range of voltmeters from 0-3 Volts.
Record your observation
The Least count of galvanometer converted into voltmeter = V/n =
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Reading of galvanometer into voltmeter
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Standard voltmeter reading V2
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Standard voltmeter reading V2 – V1
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The potential difference in volts V1
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Calculation
The resistance of the given galvanometer G =
The figure of merit k =
Number of divisions in galvanometer scale n =
Current for full scale deflection = Ig = nk =
Range of conversion =
Resistance to be placed in series with galvanometer R=V/Ig-G =
Precautions
- Calculate the resistance accurately
- Use the same range conversion voltmeter should be used for verification
- Use correct length shunt wire.
Result
The value of the actual and measured value of the potential difference is very small and conversion is perfect.
Viva Voce
- On what principle does a galvanometer work?
Ans: Works on the principle of converting electrical energy into mechanical energy.
- What is a voltmeter?
Ans: It is a device used to measure the potential difference between two points of the electrical circuit.
- How is a galvanometer converted into a voltmeter?
Ans: A galvanometer is converted into a voltmeter by connecting it with high resistance.
- Can a galvanometer be used to measure heavy currents?
Ans: No
- What is the resistance of the ideal voltmeter?
Ans: infinite
How can a galvanometer be converted into an ammeter?
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