The device that is used to amplify or switch power (electrical signals) is called a transistor. Transistors are used in many electronic devices. They are manufactured using PN diodes. These PN diodes are made using semiconductors. Materials like silicon and germanium are examples of semiconductors. 

The working principle of a transistor is that the current or voltage applied to one pair of terminals will control the output current or voltage through the other pair of terminals. The minimum number of terminals in a transistor is 3. The three terminals of the transistor are called the emitter, base and the collector. The centre region of the transistor is the base. The base is very thin and lightly doped, Adding of impurity to the semiconductor is called doping. The region on the left side of the base is called the emitter, it is heavily doped and is of moderate size. The collector on the right side of the base is moderately doped and larger in size than the emitter.

The junction between emitter and base is forward biased. The collector-base junction is reverse biased.

The transistor has three wires connected to the emitter, base and collector. The wires are unevenly spaced. The wire from the collector is more separated from the base wire than the emitter wire. The transistors start working when the charge carriers like electrons or the holes start moving across the junctions of the transistor

Development of Transistors

In the year 1947-48 transistors were invented by three American physicists, John Bardeen, Walter H. Brattain and William B. Shockley. The transistors were a viable alternative for electron tubes. Transistors helped in the miniaturization of many complex circuits because of its small size, low power consumption, low heat generation and high reliability.

Transistor types

Transistors are available in different types. The most popular types of transistors are Bipolar Junction Transistor (BJT) and Field Effect Transistor (FET). The Bipolar Junction transistor is either a PNP transistor or NPN transistor. The transistor is called bipolar because it has two PN junctions. The field-effect transistor is a unipolar device, it is either n-type or p-type.

Applications of Transistor

The transistor can be used as an amplifier and as a switch. As an amplifier, the transistor amplifies the small input current. The hearing aid is an example of a transistor being used as amplifiers. The computer chip consists of many transistors, that can be switched on and switched off individually. The transistor can be put together to make the logic gates.

Do check BYJU’S pages for more interesting topics like Coulomb’s Law.

Coulomb’s law also known as the inverse-square law states that the force of attraction between two point charges is directly proportional to the product of charges and inversely proportional to the square of the distance between them.

F = k(q1q2/r2)

The proportionality constant k is equal to 1/4πε0. ε0 is the permittivity of vacuum.

The value of k is equal to 9 x 109 Nm2/C2.