2015

PHYSICS (Theory)

Full Marks: 70

Time: 3 hours

The figures in the margin indicate full marks for the questions

1. Answer the following questions: 1x8=8

- What is quantization of charge?
- Why is the Cyclotron not used to accelerate electrons?
- If R and L represent resistance and inductance respectively then what is the dimension of L/R.
- Out of the four Maxwell’s equations, which equation establishes the non-existence of magnetic monopole?
- What is the shape of the wave front of light emitted by a long neon bulb placed at a finite distance?
- Give the dimension of Planck’s constant.
- What is an?
- What is reversed Saturation Current?

2. Calculate the magnitude of electrostatic force between a proton and an electron separated by a distance. Given that magnitude of charge of proton and electron to be each and 2

Or

A. 100pF capacitor is charged by a potential difference of 100V. What is the amount of charge stored? What is the electrostatic energy stored in the capacitor? 2

3. An-identical cells each of e.m.f E and internal resistance r are connected in series. Find the expression for current in the circuit given below.

Or

Establish the following relation for drift velocity. 2

where symbols have their usual meaning.

4. A copper wire is stretched so as to increase its length by 0.2%. Calculate the percentage change in the resistance of the wire. 2

Or

A 100W heater coil is rated 200V. Find the resistance of the coil. 2

5. Show that total energy required to build up a current I in an inductor of coefficient of induction L is 2

Or

Find the expression for mutual inductance between a pair of co-axial coils. 2

6. A metal rod of length L meter rotates about one end in a vertical plane at right angles to the magnetic meridian. Frequency of revolution is f HZ. If the Horizontal component of Earth’s magnetic field is H Tesla then find the expression of induced emf between the ends of the rod. 2

Or

Find the peak current in the circuit given below: 2

7. What is power factor of an L-C-R circuit? Explain on the basis of power factor that an ideal inductor is a Wattless component. 2

Or

Why is electrical energy transmitted at high voltage from a distant power generating station? 2

8. Write down the expression for the velocity of electromagnetic wave in a medium and hence find out an expression for the refractive index of the medium. 2

Or

What is radiation pressure? 2

9. Draw a ray diagram to show the formation of final image at least distance of distinct vision by a compound microscope. 2

Or

Draw a ray diagram for the formation of an image by a reflecting telescope.

10. Obtain Bohr’s quantization condition on the basis of the wave nature of an electron. 2

Or

Describe in brief the process of gamma radiation. 2

11. What percentage of power of AM wave is carried by the side bands for modulation index m = 1? 2

Or

How is the critical frequency related to electron density in the ionosphere? 2

12. Draw the circuit diagram of a potentiometer to compare the emf of two cells and briefly describe the procedure. 3

Or

Draw the circuit diagram of a potentiometer to determine the internal resistance of a cell and briefly describe the procedure. 3

13. A coil of area A, number of turns N and resistance R is rotating in a radial magnetic field B with an angular speed w. What is the maximum power consumed by the coil? 3

Or

An AC source of is connected across in inductor having resistance and self inductance 2H. Calculate – 3

- Frequency of AC.
- Total impedance of the circuit.
- Peak value of the current flowing through the circuit.

14. Derive the expression for the equivalent focal length of a combination of two thin convex lenses in contact. 3

Or

Deduct the relation for a convex lens producing virtual image. 3

15. Establish Brewster’s Law of polarization of light. 3

Or

What is a Coherent Source? State two difference between interference and diffraction. 3

16. A monochromatic source of light operating at 200W emits photons/sec. Find the wavelength of the light. Given 3

Or

What is the de-Broglie wavelength of an electron in the Bohr’s orbit of radius in hydrogen atom? 3

17. Derive an expression for the radius of the first orbit of the electron of the hydrogen atom. 3

Or

Obtain the binding energies of the nuclei and in units of from the given data

Which nucleus has greater binding energy per nucleon? 3

18. How is a NOT gate realised with the help of a transistor? Give its truth table. 3

Or

Of transistor are 120. What is the change in collector current forchange in base current? Draw at least two input characteristics of a CE mode transistor. 3

19. What is breakdown voltage of a Zener diode? Explain its use as a voltage regulator. 3

Or

Draw a circuit diagram of a full wave rectifier and explain its working. 3

20. What is digital communication? Mention two advantages of digital communication. 3

Or

What are sidebands of an AM wave? Compare AM and FM wave. 3

21. Define electric dipole and dipole moment. Derive an expression for electric field intensity at a point on the axial line of an electric dipole. 5

Or

Explain the concept of electric field. Express electric flux through a surface in terms of electric field intensity. Show that the electric flux through a cylindrical surface with its axis parallel to a uniform electric field is zero. 5

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