Science (English Medium) Class 12 - CBSE Question Bank Solutions

In the depletion region of a diode ______.

1. there are no mobile charges.
2. equal number of holes and electrons exist, making the region neutral.
3. recombination of holes and electrons has taken place.
4. immobile charged ions exist.

The breakdown in a reverse biased p–n junction diode is more likely to occur due to ______.

1. large velocity of the minority charge carriers if the doping concentration is small.
2. large velocity of the minority charge carriers if the doping concentration is large.
3. strong electric field in a depletion region if the doping concentration is small.
4. strong electric field in the depletion region if the doping concentration is large.

Can the potential barrier across a p-n junction be measured by simply connecting a voltmeter across the junction?

(a)

(b)

1. Name the type of a diode whose characteristics are shown in figure (A) and figure (B).
2. What does the point P in figure (A) represent?
3. What does the points P and Q in figure (B) represent?

A Zener of power rating 1 W is to be used as a voltage regulator. If zener has a breakdown of 5 V and it has to regulate voltage which fluctuated between 3 V and 7 V, what should be the value of Rs for safe operation (Figure)?

If each diode in figure has a forward bias resistance of 25 Ω and infinite resistance in reverse bias, what will be the values of the current I₁, I₂, I₃ and I₄?

In the circuit shown in figure, when the input voltage of the base resistance is 10 V, V_be is zero and V_ce is also zero. Find the values of I_b, I_c and β.

Consider a box with three terminals on top of it as shown in figure (a):

(a)

Three components namely, two germanium diodes and one resistor are connected across these three terminals in some arrangement. A student performs an experiment in which any two of these three terminals are connected in the circuit shown in figure (b).

(b)

The student obtains graphs of current-voltage characteristics for unknown combination of components between the two terminals connected in the circuit. The graphs are

(i) when A is positive and B is negative

(c)

(ii) when A is negative and B is positive

(d)

(iii) When B is negative and C is positive

(iv) When B is positive and C is negative

(f)

(v) When A is positive and C is negative

(g)

(vi) When A is negative and C is positive

(h)

From these graphs of current-voltage characteristics shown in figure (c) to (h), determine the arrangement of components between A, B and C.

The temperature (T) dependence of resistivity of materials A and material B is represented by fig (i) and fig (ii) respectively. Identify material A and material B.

fig. (i)

fig. (ii)

The graph of potential barrier versus width of depletion region for an unbiased diode is shown in graph A. In comparison to A, graphs B and C are obtained after biasing the diode in different ways. Identify the type of biasing in B and C and justify your answer

‘A’	‘B’	‘C’

Radiation of frequency 10¹⁵ Hz is incident on three photosensitive surfaces A, B and C. Following observations are recorded:

Surface A: no photoemission occurs

Surface B: photoemission occurs but the photoelectrons have zero kinetic energy.

Surface C: photo emission occurs and photoelectrons have some kinetic energy.
Using Einstein’s photo-electric equation, explain the three observations.

Two long straight parallel conductors carrying currents I₁ and I₂ are separated by a distance d. If the currents are flowing in the same direction, show how the magnetic field produced by one exerts an attractive force on the other. Obtain the expression for this force and hence define 1 ampere.

Draw V-I characteristics of a p-n Junction diode.

Differentiate between the threshold voltage and the breakdown voltage for a diode.

Write the property of a junction diode which makes it suitable for rectification of ac voltages.

Explain the formation of the barrier potential in a p-n junction.

Beams of electrons and protons move parallel to each other in the same direction. They ______.

A hydrogen atom makes a transition from n = 5 to n = 1 orbit. The wavelength of photon emitted is λ. The wavelength of photon emitted when it makes a transition from n = 5 to n = 2 orbit is ______.

• Assertion (A): Work done in moving a charge around a closed path, in an electric field is always zero.
• Reason (R): Electrostatic force is a conservative force.

Answer the following giving reasons:

A p-n junction diode is damaged by a strong current.