Electronic Voltmeter

Q. Two different voltmeters are used to measure the voltage across resistor $R_B$ in the circuit shown below.

The meters are as follows.

$MeterA:S=1k\Omega /V,R_m=0.2k\Omega ,range=10V$

$MeterB:S=20k\Omega /V,R_m=1.5k\Omega ,range=10V$

Voltage across $R_B$ when meter A, meter B are used respectively

1. 3.53 V, 4.9 V
2. 4.9 V, 3.53 V
3. 3.53, V 4.2 V
4. 3.2 V, 4.9 V

Q. In the DC milli voltmeter circuit shown in figure, the input voltage for full scale deflection is

1. 10 V
2. 1 V
3. 100 mV
4. 10 mV

Q. The op-amp based circuit of a half wave rectifier electronic voltmeter shown below uses a PMMC ammeter with a full scale deflection (FSD) current of 1 mA and a coil resistance of $1k\Omega .$ The value of R that gives FSD for a sinusoidal input voltage of 100 mV (RMS) is

1. $45\Omega$
2. $67.5\Omega$
3. $100\Omega$
4. $144.4\Omega$

Q.

An ac source of angular frequency ω is fed across a resistor R and a capacitor C in series. The current registered is I . If now the frequency of the source is changed to $\frac{\omega }{3}$ (but maintaining the same voltage), the current in the circuit is found to be halved. The ratio of the reactance to resistance at the original frequency ω is given as $\sqrt{\frac{x}{5}}$. Find x .

Q. A 50 V range voltmeter is connected across the terminals A and B of the circuit shown in figure below. If the voltmeter resistance is $1000k\Omega$, then the loading error is

1. -9.1%
2. -8.1%
3. -7.1%
4. -6.1%