A galvanometer with a full-scale deflection of 20 mA is C...
A galvanometer with a full-scale deflection of 20 mA is Converted to read 8 K by connecting a 395 Ω resistor in series with it. Determine the internal resistance of the galvanometer
2.5Ω
5.0Ω
8.0Ω
10.0Ω
Correct answer is B
r = resistance of the galvanometer
l = current through galvanometer = 20mA or 0.02A
V1 = p.d across the galvanometer = I X r = 0.02 X r
: V1 = 0.02r
V2 = p.d across the multiplier = 8 - 0.02r
R = resistance of the multiplier = 395Ω
where R = VI
--> 395 = 8−0.02r0.02
CROSS MULTIPLY
8−0.02r = 395 * 0.02
8−0.02r = 7.9
--> 0.02r = 8 - 7.9
∴ r = 0.10.02
= 5Ω