please answer this :

Question

A galvanometer has an internal resistance of 12  and requires 0.01 A for full scale

deflection. To convert it to a voltmeter reading 3 V full scale, one must use a series resistance of:

A) 102 

B) 288 

C) 300 

D) 360 

E) 412 

Answer 1

You want the "voltmeter" to measure 3V across a resistor and the galvanometer resistance in series. Since you want the galvanometer to be reading full scale, that will happen when the current is .01 amps:

V = I(R+r) or, solving for R: V/I - r = R 3V/.01 amps - 12 Ω

Take care.