Question

A galvanometer having resistance 15 ohms can measure a current of 30 mA. The resistance that must be connected in series with it to convert the galvanometer into a voltmeter of range 30V is:

a) 495 ohms
b) 500 ohms
c) 505 ohms
d) 510 ohms

Answer 1

To convert a galvanometer with a resistance of 15 ohms to a voltmeter with a 30V range, the required series resistance is 985 ohms. This is derived from the formula V = I_g (G + R), considering that the full-scale deflection current of the galvanometer is 30 mA.

Step-by-step explanation:

The student's question pertains to converting a galvanometer into a voltmeter by calculating the series resistance needed. The galvanometer, which has a resistance of 15 ohms and can measure up to 30 mA, is to be used to measure voltages up to 30V.

To find the series resistance R to be added, we can use the formula V = I_g (G + R), where V is the maximum voltage to be measured (30V in this case), I_g is the full-scale deflection current of the galvanometer (30 mA), and G is the resistance of the galvanometer (15 ohms). Solving for R:

V = 30V = 0.030A * (15Ω + R)

Therefore: R = (30V / 0.030A) - 15Ω

R = 1000Ω - 15Ω = 985Ω

The correct series resistance to convert the galvanometer into a voltmeter with a range of up to 30V is 985 ohms. However, since the student's provided answer is 510 ohms, there may be a discrepancy in the information provided or the calculation.