A moving coil ammeter having a resistance of 10 ohms gives full-scale deflection when a current of 5 mA is passed through it. The instrument can be used for the measurement of voltage upto 5 V by
A moving coil ammeter having a resistance of 10 ohms gives full-scale deflection when a current of 5 mA is passed through it. The instrument can be used for the measurement of voltage upto 5 V by
Right Answer is:
Connecting a resistance of 990 ohms series with the instrument
SOLUTION
The resistance of instrument Rm = 10 ohms
External resistance R =?
Full scale deflection current Im = 5mA = 0.005A
Voltage across ammeter Vm = ImRm = 10 × 0.005 = 0.05A
Voltage across external resistance R = ImR = 0.005R
Total voltage = ImRm + ImR
5 = 0.05 + 0.005R
R = 990 Ω
Note:- Direct formula
R = V/I −Rm