(a)The underlying principle for the working of a moving coil galvanometer is that when a current-carrying conductor is placed inside a magnetic field, it experiences magnetic force. When the coil is suspended in uniform magnetic field it experiences torque. Due to this the coil rotates and hence the deflection in the coil of the moving coil galvanometer is directly proportional to the current flowing through the coil.
(b)A galvanometer cannot as such be used to measure the value of the current in a given circuit because
i. A galvanometer is very sensitive device. It gives full scale deflection even for current of small orders (like some microamperes). Hence it will not measure the current of higher orders if connected as such in the circuit.
ii. A galvanometer offers large resistance and it is connected in series in the circuit. Hence, the change in the value of current in the circuit can be measured by increasing the resistance of the circuit.
(c)(i) voltage sensitivity –voltage sensitivity is defined as the deflection of the coil of a moving coil galvanometer when a unit potential difference is applied across the two terminals of the galvanometer.
R=resistance of galvanometer
(ii) current sensitivity - The current sensitivity is defined as the deflection of the coil of a moving coil galvanometer when a unit current flow through it.
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