Question

The full-scale deflection current of a meter is 4 mA and its internal resistance is 400Ω. This meter is to have full deflection when 400 V is measured. What is the value of the series resistor to be used?

(a) 99.90 kΩ

(b) 100 kΩ

(c) 99.60 kΩ

(d) 100 Ω

The question was asked during an interview.

Asked question is from Advanced Problems on Indicating Instruments in division Extension of Instrument Ranges of Electrical Measurements

Answer 1

Right option is (c) 99.60 kΩ

The best I can explain: (RS + 400) × 10^-3 × 4 = 400

Or, RS = 100000 – 400 = 99.6 kΩ.