Science (English Medium) कक्षा १२ - CBSE Important Questions for Physics

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.

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 ?

Describe briefly, with the help of a diagram, the role of the two important processes involved in the formation of a p-n junction.

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.

Describe briefly the following term:

minority carrier injection in forward biasing.