PHYSICS-3 MODEL PAPER

B.Sc., DEGREE (PHYSICS-PAPER-III)

Paper III - ELECTRICITY, MAGNETISM AND ELECTRONICS

Time : Three hours                                                              Maximum: 100 marks

SECTION A - (4 x 15 = 60 marks)

Answer ALL questions.

1.    (a)  Deduce the differential form of Gauss law.Derive Coulomb's law from Gauss  

           law.

Or

(b)  Obtain the expressions for capacitance of a capacitor without dielectric and 

      with dielectric in between the plates of a capacitor.

2.    (a)  What is a magnetic shell? Calculate the magnetic potential and magnetic field 

           strength due to a magnetic shell.

Or

       (b)  State the laws of electromagnetic induction and explain the principle and working 

            of Ballistic galvanometer.

3.    (a)  Derive an expression for the growth and decay of current in C-R circuit having 

          a DC source. What is meant by time constant?

Or

        (b)  Describe Hertz experiment for the production and detection of electromagnetic 

              waves.

          4.    (a)  Discuss the working of half wave rectifier and full wave rectifier.

Or

          (b)  State and prove De Morgan's theorem with examples.

SECTION B - (5 x 4 = 20 marks)

Answer any FIVE of the following.

5.    Derive an expression for mechanical force on a charged conductor.

          6.    Explain the boundary conditions at the dielectric surface.

          7.    Explain the working of cyclotron.

          8.    Explain the principle of Betatron.

          9.     State and explain Poynting theorem.

10. Explain Biot-Savarts law.

11. Mention the differences between intrinsic and extrinsic semiconductors.

12. What are universal gates? Explain with truth tables.

SECTION C - (5 x 4 = 20 marks)

Answer any FIVE of the following.

 13. Find the intensity of electric field at a point 0.25 m away from a point  charge  

         having a charge of 0.1 x 10 ^-9C.

14. Dielectric constant of a medium is 3.5. Find its permittivity and susceptibility.

15. Outer and inner radii of two spherical condenser are 9 cm, 10 cm. What is the 

     capacity when air is in between the two spheres?

16. A wire of 1m long carrying 10 Amp current is placed in a magnetic field of induction 

    1.5 w/m². If the conductor is making an angle 30⁰ with the direction of magnetic field,    

     find the force acting on the conductor.

17. Calculate Self inductance of a solenoid of length 1m and area of cross section 

      0.01sq.m. with 2000 turns.

18. What is the resonant frequency of LCR series circuit. L = 5mH, C =0.1µf,R = 100kΩ.

19. In a transistor circuit the base current changes from 50 µA to 150 µ A Collector  

      current changes from 0.2 mA to 4.2 mA Calculate its current gain .

20. Convert the given binary number into decimal number:

a.    1111₂

b.    1101₂