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

Draw a circuit diagram of a transistor amplifier in CE configurations.
Define the terms: (i) Input resistance and (ii) Current amplification factor. How are these determined using typical input and output characteristics?

Answer the following questions:
(a) In a double slit experiment using light of wavelength 600nm, the angular width of the fringe formed on a distant screen is 0.1°. Find the sapcing between the two slits.
(b) Light of wavelength 5000Å, propagating in air gets partly reflected from the surface of water. How will the wavelength and frequencies of the reflected and refracted light be affected?

A group of students while coming from the school noticed a box marked "Danger H.T. 2200 V" at a substation in the main street. They did not understand the utility of such a high voltage, while they argued, the supply was only 220V. They asked their teacher this question the next day. The teacher thought it to be an important question and therefore explained to the whole class.
Answer the following questions:
(i) What device is used to bring the high voltage down to low voltage of a.c. current and what is the principle of its working?
(ii) Is it possible to use this device for bringing down the high d.c. voltage to the low voltage? Explain.
(iii)

(a) State Ampere's circuital law. Use this law to obtain the expression for the magnetic field inside an air cored toroid of average radius 'r' having 'n' turns per unit length and carrying a steady current I.
(b) An observer to the left of a solenoid of N turns each of cross section area 'A' observes that a steady current I in it flows in the clockwise direction. Depict the magnetic field lines due to the solenoid specifying its polarity and show that it acts as a bar magnet of magnetic moment m = NIA

(a) Define mutual induactance and write its S.I. unit.

(b) In an experiment, two coils c₁ and c₂ are placed close to each other. Find out the expression for the emf induced in the coil c₁ due to change in the current through the coil c₂.

(a) Using Huygen's construction of secondary wavelets explain how a diffraction pattern is obtained on a screen due to a narrow slit on which a monochromatic beam of light is incident normallly.
(b) Show that the angular width of the first diffraction fringe is half that of the central fringe.
(c) Explain why the maxima at 𝜃 = (n+1/2)λ/a become waeker and weaker with increasing n.

(a) A point object 'O' is kept in a medium of refractive index n₁ in front of a convex spherical surafce of radius of curvature R which seperates the second medium of refractive index n₂ from the first one, as shown in the figure.

Draw the ray diagram showing the image formation and deduce the relationship between the object distance and the image distance in terms of n₁, n₂ and R.
(b) When the image formed above acts as a virtual object for concave spherical, surface seperating the medium n₂ from n₁ ( n₂ > n₁), draw this ray diagram and write the similar (simiar to (a)) re

(a) An electric dipole of dipole moment p (vector)
consists of point charges +q and -q
separated by a distance 2a apart. Deduce the expression for the electric field
E (vector)
due to the dipole at a distance x from the centre of the dipole on its axial
line in terms of the dipole moment p (vector)
. Hence show that in the limit x >> a,

E(vector)--->2 p / (4𝛱𝜀ₒx³).
(b) Given the electric field in the region

E (vector)= 2x i(cap) , find the net electric flux through
the cube and the charge enclosed by it.