Question

Assuming ideal opamp, the RMS voltage (in mV) in the output $V_0$ only due to the 230 V, 50 Hz interference is (up to one decimal place)

• A. 10.84

Answer 1

The correct option is A 10.84

When voltage at the output due to only 230 V, 50 Hz supply is to be calculated, the DC supply should be short circuited as shown below.

C${}_3$ and 10 k$\Omega$ does not play any role in the value of V${}_0$. So, the reduced equivalent circuit can be given as shown below.


$V_0=-\frac{50k\Omega }{1/j\omega C_1}{V}_i=-j\omega C_1\left(50k\right)V_i$

$V_0\left(rms\right)=(2\pi \times 50)\times 3\times {10}^{-12}\times 50\times {10}^3\times V_{i\left(rms\right)}$

= $2\pi \times 75\times {10}^{-7}\times 230V$

$=\frac{345\pi }{100}mV=10.84mV$