Physics 9702 · AS & A Level · Characteristics of alternating currents

Characteristics of alternating currents — practice question

(a)[2]

Describe what frequency modulation (FM) means.

(b(i))[1]

A sinusoidal carrier wave possesses a frequency of $600\,\text{kHz}$ and an amplitude of $5.0\,\text{V}$. A sinusoidal wave of frequency $7.0\,\text{kHz}$ and amplitude $2.0\,\text{V}$ is used to frequency modulate the carrier wave. The frequency deviation of the carrier wave is $20\,\text{kHz V}^{-1}$. Determine, for the modulated carrier wave, the amplitude.

(b(ii))[1]

Determine the maximum frequency of the modulated carrier wave.

(b(iii))[1]

Determine the minimum frequency of the modulated carrier wave.

(b(iv))[1]

Determine the number of times per second that the frequency falls from maximum to minimum and then returns to maximum.

(b)

A sinusoidal carrier wave has a frequency of $600\,\text{kHz}$ and an amplitude of $5.0\,\text{V}$. A sinusoidal wave with frequency $7.0\,\text{kHz}$ and amplitude $2.0\,\text{V}$ frequency modulates the carrier wave. The frequency deviation of the carrier wave is $20\,\text{kHz V}^{-1}$. Determine, for the modulated carrier wave, the quantities in parts (i) to (iv).

Worked solution & mark scheme

This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: The carrier-wave frequency changes in step with the displacement of the information signal

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