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Current Electricity

Question
CBSEENPH12038979

Define the current sensitivity of a galvanometer. Write its S.I. unit. Figure shows two circuits each having a galvanometer and a battery of 3 V. When the galvanometers in each arrangement do not show any deflection, obtain the ratio R1 / R2

Solution

Current sensitivity is defined as the ratio of deflection produced in the galvanometer to the current flowing through it.

 Mathematically it is given as, 
Current space Sensitivity comma space straight s subscript straight i space equals space straight theta over straight I

SI unit is radian per ampere.

No current flows through the galvanometer for balanced Wheatstone bridge.
4 over straight R subscript 1 space equals space 6 over 9 space

rightwards double arrow space R subscript 1 space equals space fraction numerator 4 space x space 9 over denominator 6 end fraction space equals 6 space capital omega
a n d space

6 over 12 space equals space R subscript 2 over 8 space

rightwards double arrow space R subscript 2 space equals fraction numerator 6 space x space 8 space over denominator 12 end fraction

therefore space R subscript 1 over R subscript 2 space equals space 6 over 4 equals 3 over 2