Science (English Medium) Class 12 - CBSE Important Questions for Physics

Write the functions of three segments of a transistor.

Distinguish between 'intrinsic' and 'extrinsic' semiconductors

With what considerations in view, a photodiode is fabricated? State its working with the help of a suitable diagram.

Even though the current in the forward bias is known to be more than in the reverse bias, yet the photodiode works in reverse bias. What is the reason?

Define the terms : Input resistance How are these determined using typical input and output characteristics?

Define the terms :Current amplification factor. How are these determined using typical input and output characteristics?

Write the truth table for the combination of the gates shown. Name the gates used.

Identify the logic gates marked 'P' and 'Q' in the given circuit. Write the truth table for the combination.

Using the necessary circuit diagrams, show how the V-I characteristics of a p-n junction are obtained in

Forward biasing

How are these characteristics made use of in rectification?

Using the necessary circuit diagrams, show how the V-I characteristics of a p-n junction are obtained in

Reverse biasing

How are these characteristics made use of in rectification?

Differentiate between three segments of a transistor on the basis of their size and level of doping.

How is a transistor biased to be in active state?

With the help of necessary circuit diagram, describe briefly how n-p-n transistor in CE configuration amplifies a small sinusoidal input voltage. Write the expression for the ac current gain

Under what condition does the transistor act as an amplifier?

Explain, with the help of a circuit diagram, the principle and working of a Zener diode as voltage regular.

Explain, with the help of a circuit diagram, the working of a photo-diode. Write briefly how it is used to detect the optical signals.

Mention the important considerations required while fabricating a p-n junction diode to be used as a Light Emitting Diode (LED). What should be the order of band gap of an LED if it is required to emit light in the visible range?

The graph shown in the figure represents a plot of current versus voltage for a given semiconductor. Identify the region, if any, over which the semiconductor has a negative resistance.

Draw typical output characteristics of an n-p-n transistor in CE configuration. Show how these characteristics can be used to determine output resistance.

Draw V − I characteristics of a p-n junction diode. Answer the following questions, giving reasons:

(i) Why is the current under reverse bias almost independent of the applied potential up to a critical voltage?

(ii) Why does the reverse current show a sudden increase at the critical voltage?

Name any semiconductor device which operates under the reverse bias in the breakdown region.

Show on a graph, the variation of resistivity with temperature for a typical semiconductor.