Question

At the input an amplifer has a signal voltage level of $3\mu V$ and a noise voltage level of $1\mu V.$ If the voltage gain of the amplifier is 20, what is the S/N ratio at the output?

• A. 1/3
• B. 1/9
• C. 3
• D. 9

Answer 1

The correct option is D 9

Voltage level of signal at the output

$=20\times 3=60\mu V$

Voltage level of noise at the output

$=20\times 1=20\mu V$

$\therefore$ Signal to noise ratio at the output is,

$={\left(\frac{60\times {10}^{-6}}{20\times {10}^{-6}}\right)}^2=9$