Transistor can be used as :-

Options

A. amplifier
B. modulator
C. oscillator
D. all of the above

Answer

To solve the question "Transistor can be used as:", we need to explore the various applications of transistors. Let's break it down step by step.

### Step 1: Understanding Transistors
Transistors are semiconductor devices that can amplify or switch electronic signals and electrical power. They come in two main types: NPN and PNP.

### Step 2: Identifying Uses of Transistors
1. **Amplifier**: Transistors can increase the amplitude of AC signals. This process is known as amplification. Therefore, transistors are used as amplifiers.

2. **Modulator**: Transistors can also be used to modulate signals. They can increase the frequency of an AC input signal, which is essential in communication systems. Thus, transistors can function as modulators.

3. **Oscillator**: Transistors can convert DC signals into AC signals. This ability allows them to function as oscillators, generating continuous waveforms.

### Step 3: Conclusion
Based on the above uses, we can conclude that transistors can serve multiple functions:
- They can act as amplifiers.
- They can function as modulators.
- They can operate as oscillators.

Thus, the correct answer to the question is that transistors can be used as **all of the above** (amplifier, modulator, and oscillator).

### Final Answer
Transistor can be used as:
- Amplifier
- Modulator
- Oscillator
- All of the above (Correct)

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