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

To solve the question regarding the type of modulation where pulse duration varies in accordance with the modulating signal, we can follow these steps:

### Step 1: Understand the Types of Modulation
- Modulation is a technique used to encode information onto a carrier signal. There are various types of modulation techniques, including Pulse Amplitude Modulation (PAM), Pulse Position Modulation (PPM), Pulse Width Modulation (PWM), and Pulse Code Modulation (PCM).

### Step 2: Analyze the Given Options
- **PAM (Pulse Amplitude Modulation)**: In PAM, the amplitude of the pulses varies according to the modulating signal, not the duration.
- **PPM (Pulse Position Modulation)**: In PPM, the position of the pulse varies according to the modulating signal, not the duration.
- **PWM (Pulse Width Modulation)**: In PWM, the width (duration) of the pulses varies according to the modulating signal.
- **PCM (Pulse Code Modulation)**: In PCM, the signal is converted into a digital signal, and it does not involve varying pulse duration.

### Step 3: Identify the Correct Modulation Type
- Since the question specifically asks for modulation where the pulse duration varies, the correct answer is **PWM (Pulse Width Modulation)**.

### Step 4: Conclusion
- Therefore, the modulation in which pulse duration varies in accordance with the modulating signal is called **PWM**.

### Final Answer:
**PWM (Pulse Width Modulation)**

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