Please help me determine iF The current through R2 and the galvanometer is the s

Question

Please help me determine iF

The current through R2 and the galvanometer is the same. Because the devices are in parallel the voltage across them is also the same. It stands from Ohm’s Law then that the resistance is also the same. Therefore r2=rg. Now that rg is known circuit 1 can be used to determine iF

R1 Circuit In circuit 2 the equivalent voltage and resistor R: are the same as in circuit 1. Assume also that the resistance R is known and the galvanometer reads half of full deflection. Rr is in series with the parallel combination of the galvanometer and R2, thus the same current that passes through Rr must pass through the rest of the circuit. In this case, because the galvanometer is at half of full deflection and Rris much greater than R, IF passes through R, and IF/2 passes through both the galvanometer and R. R1 R2 Circuit 2 The current through Rz and the galvanometer is the same. Because the devices are in parallel the voltage across them is also the same. It stands from Ohm's Law then that the resistance is also the same. Therefore R2 T Now that re is known circuit 1 can be used to determine I With the values known for If and , simple circuits can be used to determine unknown voltage or current for a resistor. Circuit 3 is a constructed voltmeter that can be used to find the voltage of an unknown power supply.

Explanation / Answer

Since R2 and rg are same and they are in parallel, the effective resistance of galvanometer and R2 will be rG/2 = R2/2

The total resistance of the circuit will be R1+rg/2 or R1+R2/2

Current, IF = V(R1+R2/2) = V/(R1+rG/2)

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