Question

In frequency modulated wave : (1) frequency varies with time (2) amplitude varies with time (3) both frequency and amplitude vary with time (4) both frequency and amplitude are constant

Short answer

In frequency modulated wave, frequency varies with time.

Step-by-step solution

Understanding Frequency Modulation

Frequency modulation (FM) is a method of encoding information in a carrier wave by varying the frequency of the wave. In FM, the information signal varies the frequency of the carrier wave. This results in a signal where the frequency changes over time depending on the information signal.

Examining Amplitude

In FM, the amplitude of the carrier wave remains constant. The information is not encoded by changing the amplitude, but purely by changing the frequency. Thus, the amplitude does not vary with time.

Conclusion

Based on the definitions and properties of frequency modulation, the correct statement is that only the frequency varies with time, and the amplitude remains constant.

Key concepts

FM Encoding

Frequency Modulation (FM) encoding involves transmitting information by altering the frequency of a carrier wave. Unlike other modulation techniques, such as Amplitude Modulation (AM), FM changes the frequency to encode the data. This means that the encoded signal varies in frequency according to the information being sent.
In FM encoding:

• The frequency of the carrier wave is varied.
• The amplitude of the carrier wave remains constant.

Imagine tuning a radio station. Different stations broadcast on different frequencies. When using FM encoding, the information (like music or voice) is transmitted by changing the frequency within a certain range while keeping the amplitude stable.

Carrier Wave

A carrier wave is a high-frequency electromagnetic wave that carries the information signal. In the context of frequency modulation (FM), this carrier wave is modulated to transmit the desired information.
Key aspects of the carrier wave in FM include:

• It has a consistent amplitude.
• Its frequency is varied to encode information.

The carrier wave remains at a steady amplitude so that it can travel efficiently through different mediums, like air or cables, without losing its strength. By keeping the amplitude constant, FM can reduce noise and improve the clarity of the transmitted signal. The carrier wave's frequency changes in direct response to the information signal's amplitude, which translates voice or music into variations in frequency.

Amplitude Variation

In frequency modulation (FM), the focus is on varying the frequency, not the amplitude. The amplitude of the carrier wave remains constant, which helps maintain the integrity and clarity of the signal.
Points to remember about amplitude in FM:

• Amplitude does not change over time during FM encoding.
• This constancy helps in reducing noise and enhancing signal clarity.

Imagine listening to a song transmitted over FM radio. The volume (amplitude) of the carrier wave stays the same, while the pitch (frequency) varies to create different sounds. This stability in amplitude is what helps FM signals achieve their high-quality audio transmission, even in environments with potential interference. By keeping amplitude constant, FM encoding avoids the common issues associated with amplitude variation, such as signal degradation and noise.