Question

# The value of $$R$$ for which $$20\%$$ of the main current passes through galvanometer of resistance $$80\Omega$$ is

A
10Ω
B
20Ω
C
30Ω
D
40Ω

Solution

## The correct option is C $$20\Omega$$Given : 20% of the main current passes through the galvanometer of resistance 80Ω80Ω Solution :Let the main current be "i"Since the Galvanometer and resistance R are connected in parellal so both will have same potential diffrence "v"Current through Galvanometer is 20% of iusing ohm's law we can write v=$$\frac{20}{100}i\times$$80 $$\Rightarrow$$ v=16i        Eq-(1)Left current will go through resistor R that is 80% of iusing ohm's law in resistor R v=$$\frac {80}{100}i \times$$R      $$\Rightarrow$$   v=$$\frac{4}{5}iR$$            Eq -(2)From Eq 1 and Eq 2 we get16i=$$\frac{4}{5}$$iRR=20 ohmThe Correct Opt: BPhysics

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