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NCERT Class XII Chapter
Moving Charges and Magnetism
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Question : 10
Total: 28
Two moving coil meters, M1 and M2 have following particulars :
R1 = 10 Ω, N1 = 30, A1 = 3.6 × 10–3m2, B1 = 0.25 T
R2 = 14 Ω, N2 = 42, A2 = 1.8 × 10–3m2, B2 = 0.50 T.
(The spring constants are identical for two meters).
Determine ratio of (i) current sensitivity (ii) voltage sensitivity of M2 and M1.
Solution:  
Current sensitivity of a moving coil galvanometer is defined as
C.S. =
Φ
I
 =
NAB
k
and voltage sensitivity, V.S. =
NAB
kR
(i) Ratio of current sensitivity
C.S2
C.S1
 =
N2B2A2k
N1B1A1k
 =
42×1.8×0.5×10−3×k
30×0.25×03.6×10−3×k
 = 1.4
(ii) Ratio of voltage sensitivity
V.S2
V.S1
 =
C.S2×R1
C.S1×R2
 =
7
5
×
10
14
 = 1
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