Question

To study the characteristics of a common emitter n-p-n or p-n-p transistor and tto find out values of current and voltage gains

Answer 1

It is object taken from physics manual of 12th grade class. Gain is obtained from ratio of output and input. This practical help to compare npn and pnp transistor.

Its apparatus include  

Npn transistor

Pnp transistor

30 volt battery

Voltmeter

Ammeter

Connecting wires

Voltmeter is a device that measures the volts at a given circuit.

Answer 2

In common-emitter circuit of a transistor, emitter-base make input section and emitter- collector make output section. As usual, base junction (input junction) is forward biased and collector junction (output junction) is reverse biased. ,

Resistance offered by base junction, is called input resistance (RI) It has a very small resistance due to forward biasing.

Resistance offered by collector junction, is called output resistance (R0). It has a high value due to reverse biasing.

Due to high output resistance (resistance in output section), a high resistance can be used as load resistance (RL). Generally RL = R0.

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Also emitter current (Ie) divides itself into base current (Ib) and collector current (Ic). In n-p-n transistor, Ic is about 98% of Ie, base current Ib remains only 2% of Ie. A little change in Ib causes a large change (about 49 times) in Ic. The ratio of change in collector current to the corresponding change in base current, measures current gain in common emitter transistor. It is represented by symbol β.

to-study-the-characteristics-of-a-common-emitter-npn-or-pnp-transistor-and-to-find-out-the-values-of-current-and-voltage-gains-2

For the example given above, P becomes 49.

The product of current gain and the resistance gain measures voltage gain of the common emitter transistor. It is about fifty times the resistance gain.

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