Question

A 10 V range Voltmeter is rated for 50 $\mu$A full-scale current. The total resistance of the voltmeter is_______.

• A. 100 k$\Omega$
• B. 200 k$\Omega$
• C. 300 k$\Omega$
• D. 400 k$\Omega$

Hint:

Always use Ohm’s Law to find internal resistance from voltmeter range and full-scale current: $R = V/I$.

Answer 1

The Correct Option is B

Step 1: Understand how voltmeter works.
A voltmeter measures voltage across its terminals. It's designed such that full-scale deflection happens at a certain current.
Given: \[ V = 10\ \text{V}, I = 50\ \mu A = 50 \times 10^{-6}\ \text{A} \] Step 2: Use Ohm’s Law.
\[ R = \frac{V}{I} = \frac{10}{50 \times 10^{-6}} = 200,000\ \Omega = 200\ k\Omega \] Conclusion: The total internal resistance of the voltmeter is: \[ \boxed{200\ k\Omega} \]