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RIYAS K
Conversion of Galvanometer
into Voltmeter and Ammeter
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Conversion of a Galvanometer
into Ammeter
Galvanometer: A galvanometer is a device
used to find direction of current and its
magnitude. It has small resistance and is
connected in series.
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Conversion of a Galvanometer into Ammeter
●
Ammeter: -It is a low
resistance galvanometer,
used to measure current
in a circuit.
●
It is connected in series
in a circuit.
●
An ideal ammeter have
zero resistance.
Ammeter
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It is done by connecting a low
resistance in parallel with
galvanometer.
The low resistance is called shunt
resistance.
Conversion of a Galvanometer into Ammeter
Potential drop across shunt resistance
and galvanometer are same.
(i−ig)xS=igxG
S =
ig xG
(i−ig)
ig=galavanometer current
G=resistanceof galvanometer
i=total current
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Conversion of a Galvanometer into Voltmeter
●
Voltmeter: -It is a high
resistance galvanometer,
used to measure
potential difference
between two points.
●
It is connected in
parallel in a circuit .
●
An ideal Voltmeter have
infinite resistance.
Voltmeter
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Conversion of a Galvanometer into Voltmeter
It is done by connecting a high
resistance in series with
galvanometer.
Potential drop across the
Voltmeter,
V=igx G+ig x R
V=ig(G+R)
R=
V
ig
−G
V=totalvoltage
G=resistance of galvanometer
ig=galavanometer current
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Numeric problem #1
A galvanometer coil has a resistance of 12Ω and it
shows full scale deflection at a current of 3 mA. How
would you convert it into (i) voltmeter of range 0 -18V
(ii) an ammeter of range 0 - 6A
G=12Ω
ig=3mA=3x10-3
A
i=6A
V=18V
(i)Voltmeter
R=
V
ig
−G
(ii)Ammeter
S =
ig x G
(i−ig )
Hint:
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Resistance of Ammeter
When galvanometer is converted into ammeter,
resistance decreases...
1
Ra
=
1
G
+
1
S
Ra=
G S
G+STherefore
Resistance of Voltmeter
Rv=R+G
Ammeter has very low resistance...
Voltmeter has very High resistance...
