Apr 022014

Time: 3 hours

Full Marks: 75
Pass Marks: 30

Group ‘A’

1. Attempt any four questions: [2 × 6 = 12]

a) Two wires, one of copper and other of iron, have the same diameter and carry same current. In which wire will the drift velocity of the electrons be more?
b) Why do the electrolytes have lower conductivity than metallic conductor?
c) What are hysteresis properties of ferromagnetic substance to make an electromagnet?
d) Explain why two parallel wires carrying current in opposite direction repel each other?
e) Hall voltage is much more measurable in semi-conductor than in metals. Why?
f) 220V a.c. is more dangerous than 220V d.c., why?

2. Attempt any four questions: [2 × 2 = 4]

a) If a discharge tube is filled up with various gases in turn, will the discharge in all gases take place at the same electrode potential?
b) A photon and an electron have got the same de-Brogile wavelength. Explain which has greater total energy?
c) What will happen to the number of electrons in the conduction band of a semiconductor as the temperature of the material is increased?
d) It is said that a powerful crane is required to lift a nuclear mass of microscopic size. Comment on this.
e) A particle consists of up, up and down quarks. How can we say that it is a proton?
f) What are the effects of pollution on living organisms?

3. Attempt any one question: [2 × 1 = 2]

a) How can bats fly around without colliding with objects that comes in their way?
b) Longitudinal waves cannot be polarized. Why?

4. Attempt any one question: [2 × 1 = 2]

a) Define spherical wavefront and plane wavefront.
b) How does the value of polarizing angle for a transparent medium depend upon the wavelength of light?

Group ‘B’

5. Attempt any three questions: [4 × 3 = 12]

a) State Biot-Savart’s law and use it to obtain an expression for magnetic field at the centre of circular coil.
b) What are the categories in which magnetic materials are classified? Explain their differences.
c) State Faraday’s law of electromagnetic induction. Find the expression for emf developed in a moving coil.
d) What is potentiometer? How is this used to compare emf of two cells?

6. Attempt any three questions: [4 × 2 = 8]

a) Describe Thomson’s experiment to determine the specific charge of an electron.
b) What is laser? Describe He-Ne laser.
c) Discuss P-N junction diode. How is it used as a full-wave rectifier?
d) Define decay constant of a radioactive element. How is it related to half life?

7. Attempt any one question: [4 × 1 = 4]

a) Show that both harmonics, odd and even, can be produced in an open organ pipe.
b) What is Doppler’s effect? Deduce an expression for the apparent frequency heard by a stationary observer when a source is moving towards him.

8. Attempt any one question: [4 × 1 = 4]

a) Describe Foucault’s method of determining the speed of light.
b) Show that in Young’s double slit experiment, the width of dark and bright fringes are equal.

Group ‘C’

9. Solve any three questions: [4 × 3 = 12]

a) A heating coil of power ration 10W is required when the p.d across it is 20V. Calculate the length of nichrome wire needed to make the coil if the cross sectional area of wire used is 1 × 10-7m2 and the resistivity of nichrome is 1 × 10-6 Ωm. What length of wire would be needed if its diameter was doubled?
b) At a place, the vertical component of earth’s magnetic field intensity is 0.21 × 10-4T and the angle of dip is 30o. Find the total intensity and horizontal component of earth’s magnetic field.
c) A narrow coil of 10 turns and area 4 × 10-2m2 is placed in a uniform magnetic field of flux density B of 10-2T so that the flux links the turns normally. Calculate the average induced emf in the coil if it is removed completely from the field in 0.5s. If the same coil is rotated about an axis through its middle so that it turns through 60o in 0.2s in the field B, calculate the average induced emf.
d) A circuit consists of a capacitor of 2µF and a resistor of 1000Ω. An alternating emf of 12V (r.m.s.) and frequency 50Hz is applied. Find (i) the current flowing, (ii) the voltage across the capacitor, (iii) the phase angle between the applied emf and current, (iv) the average power supplied.

10. Solve any two numerical questions: [4 × 2 = 8]

a) An electron moving with a speed of 107m/s is passed into a magnetic field of intensity 0.1T normally. What is the radius of the path of electron inside the field? If the field strength is doubled, what will be the new radius of the path? (e/m = 1.8 × 1011C/kg)
b) The maximum kinetic energy of the electrons emitted from a metallic surface is 1.6 × 10-19J when the frequency of the incident radiation is 7.5 × 1014Hz. Calculate the minimum frequency of radiation for which the electrons will be emitted. Assume that Plank’s constant is 6.62 × 10-34Js.
c) A city required 108W of electrical power on average. If this is to be supplied by a nuclear reactor of efficiency 20% by using 92U235 as the fuel, calculate the amount of fuel required for one day’s operation. (Energy released per fission of 92U235 = 200 MeV.)

11. A man standing at one ends of a closed corridor 57m long sends a short blast on a whistle. He found that the time from the blast to the sixth echo was 2 seconds. If the temperature was 17oC. What was the velocity of sound at 0oC? [4]

12. Light travelling in water strikes a glass plate at an angle of incidence of 53o, part of beam is refracted an part is reflected. IF the refracted and reflected portions make an angle of 90o with each other, what is the index of refraction of glass? [3]