Question

The voltmeter has range $10\text{ V}$ and its internal resistance is $50\Omega$. To increase the range of voltmeter to $15\text{ V}$ , the resistance which is to be connected is

• A. $125\Omega$ resistance in parallel
• B. $125\Omega$ resistance in series
• C. $25\Omega$ resistance in parallel
• D. $25\Omega$ resistance in series

Hint:

To increase voltmeter range, add resistance in series. To increase ammeter range, add resistance in parallel.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
To increase a voltmeter's range, additional resistance must be added in series to limit the voltage across the original meter.
Step 2: Key Formula or Approach:
$V = I(R_g + R_s) \implies R_s = R_g \left[ \frac{V_{new}}{V_{old}} - 1 \right]$.
Step 3: Detailed Explanation:
$R_g = 50\Omega$, $V_{old} = 10\text{ V}$, $V_{new} = 15\text{ V}$.
$R_s = 50 [15/10 - 1] = 50 [0.5] = 25\Omega$.
Step 4: Final Answer:
$25\Omega$ resistance in series.