A moving coil instrument gives full deflection with 15 mA. The instrument has the resistance of 5 ohms.

A moving coil instrument gives full deflection with 15 mA. The instrument has the resistance of 5 ohms. If resistance of 0.80 ohms is connected in parallel with the instrument, the instrument will be capable of reading upto

Right Answer is:

1087 mA

SOLUTION

The resistance of instrument Rm = 5 ohms

Shunt resistance Rs = 0.80 ohms

Full scale deflection current Im = 15mA = 0.015A

Instrument Current I =?

The shunt resistance is given as

Rs = ImRm ⁄ (I − Im)

0.80 = (0.015 × 5) ⁄ (I − 0.015)

0.80I − 0.012 = 0.075

I = 0.10875

I = 10875mA

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