1. Principle of a voltmeter

A voltmeter is connected in parallel across the resistance whose potential difference is to be measured.

For an ideal voltmeter, its resistance should be very large, so that it draws negligible current and does not disturb the circuit.

2. Examine Assertion A

Assertion A says:

For measuring the potential difference across a resistance of $600\,\Omega$, the voltmeter with resistance $1000\,\Omega$ will be preferred over voltmeter with resistance $4000\,\Omega$.

This is incorrect.

Since a voltmeter should have higher resistance, the voltmeter of resistance $4000\,\Omega$ is preferred over the one of resistance $1000\,\Omega$.

Reason: when connected in parallel with the $600\,\Omega$ resistor, the effective resistance changes less if the voltmeter resistance is larger.

To see this:

• With $1000\,\Omega$ voltmeter, $R_{\text{eq}}=\frac{600\times 1000}{600+1000}=375\,\Omega$

• With $4000\,\Omega$ voltmeter, $R_{\text{eq}}=\frac{600\times 4000}{600+4000}\approx 521.7\,\Omega$

The second case disturbs the original $600\,\Omega$ resistor much less. So the $4000\,\Omega$ voltmeter is better.

Hence, Assertion A is false.

3. Examine Reason R

Reason R says:

Voltmeter with higher resistance will draw smaller current than voltmeter with lower resistance.

This is correct.

From Ohm’s law, $I=\frac{V}{R}$ for the same potential difference $V$, a larger resistance means smaller current.

So a high-resistance voltmeter draws less current.

Hence, Reason R is true.

4. Choose the correct option

• Assertion A: False
• Reason R: True

Therefore, the correct option is:

$\boxed{\text{A}}$

5. Comparison with stored answer

Stored correct answer: A

My derived answer: A

So, they agree.