Figure shows a light bulb (B) and iron cored inductor connected to a dc battery through a switch (S).

1. What will one observe when switch (S) is closed?
2. How will the glow of the bulb change when the battery is replaced by an ac source of rms voltage equal to the voltage of dc battery? Justify your answer in each case.

Obtain the resonant frequency and Q-factor of a series LCR circuit with L = 3.0H, C = 27μF, and R = 7.4Ω. It is desired to improve the sharpness of the resonance of the circuit by reducing its ‘full width at half maximum’ by a factor of 2. Suggest a suitable way.

1. Explain briefly the process of emission of light by a Light Emitting Diode (LED).
2. Which semiconductors are preferred to make LEDs and why?
3. Give two advantages of using LEDs over conventional incandescent lamps.

How are electromagnetic waves produced? What is the source of energy of these waves? Draw a schematic sketch of the electromagnetic waves propagating along the + x-axis. Indicate the directions of the electric and magnetic fields. Write the relation between the velocity of propagation and the magnitudes of electric and magnetic fields.

Find the time required for a 50Hz alternating current to change its value from zero to the rms value.

Draw the effective equivalent circuit of the circuit shown in Fig, at very high frequencies and find the effective impedance.

Define the electric resistivity of a conductor.
Plot a graph showing the variation of resistivity with temperature in the case of a (a) conductor, (b) semiconductor.
Briefly, explain, how the difference in the behaviour of the two can be explained in terms of number density of charge carriers and relaxation time.

Consider the situation of the previous problem. Find the average electric field energy stored in the capacitor and the average magnetic field energy stored in the coil.

1. In Young's double slit experiment, two slits are 1 mm apart, and the screen is placed 1 m away from the slits. Calculate the fringe width when light of wavelength 500 nm is used.
2. What should be the width of each slit in order to obtain 10 maxima of the double slits pattern within the central maximum of the single slit pattern?

1. Describe the working of photodiode by drawing the circuit diagram.
2. Draw the characteristics of a photodiode for different illumination intensities.
3. Why is photodiode operated in reverse bias even though the reverse bias current is much weaker than the current in forward bias?