You can also get Class XII Practicals on Biology, Physics, and Physical Education.
Aim : To convert the given galvanometer into a voltmeter of desired range and to verify the same .
Apparatus : A Weston type galvanometer , a voltmeter of 0-3 V range , a battery eliminator , two resistance boxes , the one way key , a rheostat , connecting wires .
Theory : the series resistance required for conversion ,
R=V/Ig-G
Where V is the range of conversion .
Procedure :
- Calculate the value of series resistance R to be connected In series with the galvanometer for the given V .
- Connect a resistance box in series with the galvanometer and take out the plug of R . The galvanometer is now ready for use as voltmeter of range V volts .
- For verification , make the connection as shown in diagram . A and B are the fixed terminals and C is the variables terminals .
- Take out the plugs of calculated R from the resistance box . Insert a key K and adjust the movable contact of the rheostat so that deflection in the galvanometer becomes maximum .
- Note the readings of voltmeter and galvanometer . Convert the galvanometer reading into volts.
- Find the difference , if any between the readings of voltmeter and galvanometer . The difference gives the error .
- Move the variable contact C and take five observation covering whole range of voltmeter .
- Record your observation.
Result
As the difference in actual and measured value of potential difference is very small , the conversion is perfect .
Precaution
1. Length of the shunt wire should be neither too short nor too long .
2. The voltmeter used for verification should preferable be of the same range as the range of conversion .
3. Value of required series resistance should be calculated accordingly .
Sources of error
The connection may be loose .
The emf of the cell or battery may be variable .
Circuit diagram :-
Observation
Resistance of given galvanometer (G) 60 ohm
No of division (n)=10
Current (Jg) =nk=0.00028A
Range of conversion = V
=0-3 V
Resistance to be placed in series = Rs
Rs =V/Ig-G
Rs =3/0.00028 -60.7
Rs = 10653.5 Ohm
Verification
V1 =3V
V2=2.8 V
% error = 3-2.8/3 x 100
=0.2/3 x 100
=6.67 %
Viva question
Why is a Galvanometer not suitable to work as an ammeter .
A galvanometer has more resistance and less current . carrying capacity from those required in ammeter . It will damage if large current flows through it .
What is a shunt ?
A small resistance connected in parallel with a galvanometer is called shunt .
Why is a galvanometer not suitable to work as voltmeter ?
A galvanometer has less resistance and more current carrying capacity from those required by a voltmeter .
How is a galvanometer converted into a voltmeter ?
A galvanometer is converted into a voltmeter by connecting a high resistance in series with the galvanometer coil.
What happens when a voltmeter is converted in series in a circuit ?
The voltmeter cannot measure the potential difference in the circuit because overall resistance of circuit increases .
You can also get Class XII Practicals on Biology, Physics, and Physical Education.
Where is observation table?
Please show that also.
Please give an observation table also
Show the observation table
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