Is an amplifier a BJT?

This may sound stupid, but I'm sort of confused

A BJT is a bipolar junction transistor.

It is a not very linear current gain device. Specifically in a certain range of voltages the emitter-collector current is a fairly constant multiple (called beta) as the current going into the base. Beta varies a lot between devices and over temperature, however a nominal value is about 100 for non specialized devices.

A BJT with a couple of resistors can be configured into a nice linear voltage or current amplifier. The resistors are used to create feedback that trades amplification for linearity.
A BJT is a "Bipolar Junction Transistor."

You can use them to build an amplifier. It is just one type of transistor.
an amp. has components,C,R,L..and BJT,FET,LED,,(and years ago vacume tubes)
It can be used as an amplifier, but is not necessarily an amplifier in and of itself. A BJT is as described by the other respondent. What I believe that you need to understand is that a BJT or the FET, or MOS-FET, and other similar semi-conductors are electronic devices that control the flow of electricity. They can amplify, detect, or oscillate with the appropriate circuit components to achieve the desired function. Any of these devices though, are not just an amplifier. They are control devices that can be used as already described.
A point of history, a "BJT", was at one time referred to as a transistor. It wasn't until other similar types of "transistors" came into wide spread use that the differentiations became needed. The name "transistor" comes from what the device actually was first called. When invented, this device was called a "transfer resistor". That is how the word transistor came into being.
The question is backwards really. A BJT is an amplifier.

An amplifier is a device that takes a small signal and increases it's magnitude.

Within certain limits, a BJT can act as an amplifier. There are other discrete devices that can do the same.

Amplifiers can also be multi part circuits including ICs. For example, a sound amplifier takes a small signal and boosts it for use by speakers. It does this with many parts and stages of amplification. An example of an IC amplifier is an operational amplifier. This is a muti stage amplifier with many parts on a single chip.

The answers post by the user, for information only, does not guarantee the right.

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