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LPSC (ISRO) Technician B (Electronic Mechanic): Previous Year Paper (Held on 4 March 2018)

Option 3 : 1200

CT 1: Current Affairs (Government Policies and Schemes)

54676

10 Questions
10 Marks
10 Mins

__Concept:__

Two or more amplifier circuits can be cascaded to increase the gain of an ac signal.

The overall gain Av can be calculated by simply multiplying each gain together. This is as shown:

Mathematically, this is defined as:

\({{\rm{A}}_{\rm{v}}} = {{\rm{A}}_{{{\rm{v}}_1}}}\times {{\rm{A}}_{{{\rm{v}}_2}}}\times {{\rm{A}}_{{{\rm{v}}_3}}} \ldots .\)

In dB, the overall gain is defined as:

\({A_v}\left( {dB} \right) = 20\;log{A_v}\)

This can be written as:

\({A_v}\left( {dB} \right) = 20\;log{A_v} = 20\;{\rm{log}}({A_{{v_1}}}\times {A_{{v_2}}}\times {A_{{v_3}}} \ldots .\;\)

\({A_v}\left( {dB} \right) = 20log{A_{v1}} + 20\;log{A_{v2}} + \;20\;log{A_{v3}}\; + \ldots \)

Hence,

\({A_v}\left( {dB} \right) = {A_{v1\left( {dB} \right)}} + {A_{v2\left( {dB} \right)}} + \;{A_{v3\left( {dB} \right)}}\; + \; \ldots \)

**∴ If the gain of each amplifier stage is expressed in decibels (dB), the total gain will be the sum of the gains of individual stages.**

__Calculation:__

The voltage gain of 1st amplifier = 30

The voltage gain of 2nd amplifier = 40

Voltage gain of the combined amplifier = 30 x 40 = **1200**