Q.

In a moving coil galvanometer, two moving coils M1 and M2 have the following particulars:

R1=5Ω, N1=15, A1=3.6×103m2, B1=0.25T

R2=7Ω, N2=21, A2=1.8×103m2, B2=0.50T

Assuming that torsional constant of the springs are same for both coils, what will be the ratio of voltage sensitivity of M1 and M2          [2025]

1 1 : 1  
2 1 : 4  
3 1 : 3  
4 1 : 2  

Ans.

(1)

Kθ=NIAB  θI=NABK

Voltage sensitivity =θV=θRI=NABKR

Ratio of voltage sensitivity =(N1A1B1R1)(R2N2A2B2)

Ratio =(N1A1B1N2A2B2)R2R1=15×3.6×0.2521×1.8×0.5×75=11