A signal of frequency 20 kHz and peak voltage of 5 Volt is used to modulate a carrier wave of frequency 1.2 MHz and peak voltage 25 Volts. Choose the correct statement.

JEE Main 2017 Physics question

Not in JEE or NEET syllabus

A signal of frequency kHz and peak voltage of Volt is used to modulate a carrier wave of frequency MHz and peak voltage Volts. Choose the correct statement.

(1)Modulation index , side frequency bands are at kHz and kHz.
(2)Modulation index , side frequency bands are at kHz and kHz.
(3)Modulation index , side frequency bands are at kHz and kHz.Correct
(4)Modulation index , side frequency bands are at kHz and kHz.

Answer: (3)

Solution

The **modulation index** is the ratio of the modulating (signal) amplitude to the carrier amplitude:

μ = = = 0.2.

Since there is no over-modulation, as required for faithful transmission — and this value alone eliminates options (1), (2) and (4), all of which quote

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Question ID VK-115793