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

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.

Distinguish between nuclear fission and fusion giving an example of each.

Justify your answers for each case.

State the significance of the negative value of electrostatic potential energy of a system of charges.

Three charges are placed at the corners of an equilateral triangle ABC of side 2.0 m as shown in the figure. Calculate the electric potential energy of the system of three charges.

A photon of wavelength 663 nm is incident on a metal surface. The work function of the metal is 1.50 eV. The maximum kinetic energy of the emitted photoelectrons is ______.

A semiconductor device is connected in series with a battery, an ammeter and a resistor. A current flows in the circuit. If. the polarity of the battery is reversed, the current in the circuit almost becomes zero. The device is a/an ______.