The modulation in which pulse. Duration varies in accordance with the modulating signal is called

Options

A. PAM
B. PPM
C. PWM
D. PCM

Explanation

**Step-by-Step Solution:**

1. **Understanding Modulation**: Modulation is a technique used in communication systems to encode information onto a carrier signal. It involves varying certain properties of the carrier signal based on the information signal.

2. **Identifying the Type of Modulation**: The question specifies that the modulation involves a change in pulse duration according to the modulating signal. This indicates that we are looking for a type of modulation that specifically alters the width of the pulses.

3. **Recognizing Pulse Width Modulation (PWM)**: The modulation where the duration of the pulses varies in accordance with the modulating signal is known as Pulse Width Modulation (PWM). In PWM, the width of the pulses is changed while keeping the amplitude constant.

4. **Alternative Name**: PWM is also referred to as Pulse Duration Modulation (PDM). Both terms describe the same concept of varying the duration of the pulses based on the input signal.

5. **Eliminating Other Options**: The other options mentioned (Amplitude Modulation, Frequency Modulation, and Code Modulation) do not involve varying pulse duration, thus confirming that they are not the correct answer.

6. **Conclusion**: Therefore, the modulation in which pulse duration varies in accordance with the modulating signal is called Pulse Width Modulation (PWM).

**Final Answer**: Pulse Width Modulation (PWM) or Pulse Duration Modulation (PDM).

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