In amplitude modulation

Options

A. Amplitude remains constant but frequency change
B. Both amplitude and frequency do not change
C. Both amplitude and frequency change
D. Amplitude of the carrier wave changes according to information signal

Answer

### Step-by-Step Solution:

1. **Understanding Amplitude Modulation (AM)**:
- Amplitude modulation is a technique used in electronic communication where the amplitude of a carrier wave is varied in proportion to the amplitude of the input signal (the information signal).

2. **Identifying the Components**:
- The carrier wave is a high-frequency signal that carries the information. The input signal (e.g., a voice signal) varies in amplitude, which corresponds to the loudness of the sound.

3. **Process of Amplitude Modulation**:
- When the input signal is applied to the carrier wave, the amplitude of the carrier wave changes according to the variations in the input signal. This means that the amplitude of the carrier wave is not constant; it varies based on the input signal.

4. **Comparison with Frequency Modulation (FM)**:
- In frequency modulation, it is the frequency of the carrier wave that changes based on the input signal, not the amplitude. In contrast, AM specifically involves changes in amplitude while keeping the frequency constant.

5. **Analyzing the Options**:
- A) Amplitude remains constant but the frequency changes: This is incorrect as AM involves changing amplitude.
- B) Both do not change: This is incorrect as the amplitude does change.
- C) Frequency changes: This is incorrect as the frequency remains constant in AM.
- D) Amplitude of the carrier wave changes according to the information signal: This is correct as it accurately describes the process of amplitude modulation.

6. **Conclusion**:
- The correct answer is option D, which states that the amplitude of the carrier wave changes according to the information signal.