1. Given data

• Cell emf: $V = 90\,\text{V}$
• Two resistors in series: $R_1 = R_2 = 100\,\Omega$
• Voltmeter resistance: $R_v = 400\,\Omega$

We need the reading of the voltmeter when it is connected across each $100\,\Omega$ resistor.

2. Important idea

A voltmeter has finite resistance, so when connected across a resistor, it is in parallel with that resistor.

So, if the voltmeter is connected across one $100\,\Omega$ resistor, the effective resistance of that branch becomes:

Thus the circuit becomes:

• one branch of $80\,\Omega$ (resistor in parallel with voltmeter), in series with
• the other $100\,\Omega$ resistor.

So total resistance is:

3. Find total current

Using Ohm's law,

4. Find voltage across the branch containing voltmeter

The voltmeter reads the voltage across the parallel branch, whose equivalent resistance is $80\,\Omega$.

So,

Hence the voltmeter reading is:

5. Check options

• A: $40\,\text{V}$ ✅
• B: $90\,\text{V}$ ❌
• C: $45\,\text{V}$ ❌
• D: $80\,\text{V}$ ❌

So the correct option is A.

6. Comparison with stored answer

Stored correct answer: A

Our derived answer: A

They match.