Science (English Medium) Class 12 - CBSE Important Questions

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.

The current in the forward bias is known to be more (~mA) than the current in the reverse bias (~μA). What is the reason, then, to operate the photodiode in reverse bias?

Draw a simple circuit of a CE transistor amplifier. Explain its working ?

Show that the voltage gain, A_V, of the amplifier is given by `A_v = (beta_(ac) R_1)/r_i`where β_ac is the current gain, R_L is the load resistance and r_i is the input resistance of the transistor. What is the significance of the negative sign in the expression for the voltage gain?

Draw the circuit diagram of a full wave rectifier using p-n junction diode.

Explain its working and show the output, input waveforms.

Show the output waveforms (Y) for the following inputs A and B of (i) OR gate (ii) NAND gate ?

Why a photo-diode is operated in reverse bias whereas the current in the forward bias is much larger than that in the reverse bias? Explain. Mention its two uses.

What is meant by doping of an intrinsic semiconductor?

Name the two types of atoms used for doping of Ge/Si.

In an extrinsic semiconductor, the number density of holes is 4 × 10²⁰ m^-3. If the number density of intrinsic carriers is 1.2 × 10¹⁵ m^-3, the number density of electrons in it is ______.

The formation of the depletion region in a p-n junction diode is due to ______.

Draw an energy band diagram for a p-type semiconductor at T > 0 K.

Draw the circuit arrangement for studying V-I characteristics of a p-n junction diode in (i) forward biasing and (ii) reverse biasing. Draw the typical V-I characteristics of a silicon diode.

Define modulation index.

How are side bands produced?

Draw a block diagram of a detector for AM signal and show, using necessary processes and the waveforms, how the original message signal is detected from the input AM wave.

Explain the process of amplitude modulation.