A galvanometer with resistance 1000 Ω gives full scale deflection with a current of 10 mA. The value of shunt, in order to convert it into an ammeter of 10 ampere range, will be:
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Use the shunt relation for converting a galvanometer into an ammeter.
In a moving coil galvanometer, the current I is related to the deflection θ as:
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For a moving-coil galvanometer in a radial field, deflection is directly proportional to current.
The pole pieces of the magnet in galvanometer are made concave to make the field:
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Concave pole pieces help produce a strong radial magnetic field.
To convert a galvanometer of resistance 500 Ω and current limit 2 mA into an ammeter of range 1 ampere, the resistance required is:
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Use S = IgRg/(I − Ig) for the required shunt resistance.
In order to increase the range of an ammeter, the shunt resistance is:
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A lower shunt resistance allows more current to bypass the galvanometer.
A galvanometer with resistance 50 Ω can read up to 5 mA. If this instrument is to be used to read up to 100 V, then the value of resistance to be used in its series will be:
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Use R = V/I − Rg, with full-scale current 5 mA.
The current passing through a coil of galvanometer is given by:
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From the galvanometer relation Cθ = NIAB, current is I = Cθ/(NAB).
An ammeter reads up to 1 A. Its internal resistance is 0.81 Ω. To increase the range to 10 A, the value of the required shunt is:
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The shunt carries the excess current while the ammeter coil carries its rated current.
Such a galvanometer in which the coil comes to rest quickly after the current is passed through it is called:
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A dead-beat galvanometer settles quickly without oscillation.
The effective and practical way to increase the sensitivity of a moving coil galvanometer is to:
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Sensitivity increases with the number of turns, coil area and magnetic field, with the source identifying many turns as the practical method.
The coil of a galvanometer is suspended in a radial field so that the deflecting torque on the coil is always:
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In a radial magnetic field, sin α = 1, so torque remains NIAB.
The sensitivity (I/θ) of a galvanometer is given by:
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From θ/I = NAB/C, the current sensitivity I/θ is C/(NAB).
To convert a moving coil galvanometer into voltmeter, the series high resistance (Multiplier) is given by:
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The total resistance needed is V/Ig; subtract the galvanometer resistance to obtain the series resistance.
When the coil of the galvanometer is in equilibrium, then the deflecting couple is:
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At equilibrium, the deflecting and restoring torques are equal and opposite.
Principle of working of a Galvanometer is that:
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A current-carrying coil placed in a magnetic field experiences a torque.
An ammeter measures the total current flowing through a circuit when it is connected:
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An ammeter must be connected in series so the circuit current passes through it.
To increase the measuring range of a voltmeter, the series resistance should be:
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A larger series resistance allows a voltmeter to measure a larger potential difference.
The S.I unit of galvanometer constant is:
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The galvanometer constant is current per unit angular deflection.
The galvanometer constant in a moving coil galvanometer is given by:
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Galvanometer constant is current per unit deflection: K = I/θ = C/(NAB).
In a Multi Range ammeter, as the range increases:
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A higher current range requires a smaller shunt resistance.
