Question
Tue April 17, 2012 By:
 

can you give the symbols used in a circuit diagram and a description about the galvanomtre ,voltmetre etc if any

Expert Reply
Tue April 17, 2012

 

Let resistance of galvanometer = Rg and it gives full-scale deflection when current Ig is passed through     it. Then,
Vg = IgRg -------(i)
    Let a shunt of resistance (Rs) is connected in parallel to galvanometer. If total current through the     circuit is I.
    Then current through shunt:
Is = (I-Ig)
    potential difference across the shunt:
Vs= IsRs
or 
              Vs = (I – Ig)Rs -------(ii)
    But
Vs =Vg
(I - Ig)Rs = IgRg 

 

 

oltmeter is always connected in parallel to a circuit.
SYMBOL
 
CONVERSION OF GALVANOMETER INTO VOLTMETER
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    Since Galvanometer is a very sensitive instrument, therefore it can not measure high potential     difference. In order to convert a Galvanometer into voltmeter, a very high resistance known as "series     resistance" is connected in series with the galvanometer.
VALUE OF SERIES RESISTANCE
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    Let resistance of galvanometer = Rg and resistance Rx (high) is connected in series to it. Then     combined resistance = (Rg + Rx).
    If potential between the points to be measured = V and if galvanometer gives full-scale deflection,     when current "Ig" passes through it. Then,
 
V = Ig (Rg + Rx) 
V = IgRg + IgRx 
V – IgRg = IgRx 
Rx = (V – IgRg)/Ig

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