Vous êtes sur la page 1sur 4


Find (i) the equivalent capacitance and (ii) the total energy stored in the system of capacitors given in the network. The charging battery has an emf of 4 V. 3

2. Draw a circuit diagram for a meter bridge to determine the unknown resistance of a resistor. Obtain the balance condition for a meter bridge. Why are the connections between resistors of a meter bridge made of thick copper strips? Find the shift in the balance point of a meter bridge, when the two resistors in its two gaps, are interchanged. Take the values of the two resistors as R and S. 3. In the figure shown, calculate the total flux of the electrostatic field through the spheres S1 and S2. The wire, AB, shown here, has a linear charge density , distance measured along the wire, from the end A. 3 , given by where x is the

4. An electric dipole of length 4 cm, when placed with its axis making an angle of 600 with a uniform electric field experiences a torque of Nm. Calculate the (i) magnitude of the electric field. (ii) potential energy of the dipole, if the dipole has charges of 2 5. Explain how does the resistivity of a conductor depend upon (i) number density n of free electrons, and (ii) relaxation time 2 6. State Gauss theorem in electrostatics. Using this theorem, derive an ex pression for the electric field intensity due to an infinite plane sheet of charge of charge density .

7. Deduce an expression for the capacitance of a parallel plate capacitor with air as the medium between the plates. 3 8. Define the term 'temperature coefficient of resistivity'. Write its S I unit. Plot a graph showing the variation of resistivity of copper with temperature. 3 9. The circuit diagram shows the set-up for measurement of emf generated in a thermocouple connected between points X and Y. The cell E of emf 2 V has negligible internal resistance. The potentiometer wire of length 1 m has a resistance of . The balance point S is found to be 400 mm from point P. Calculate the emf generated by the thermocouple. 3

10. An electrostatic field line cannot be discontinuous. Why? 11. A parallel capacitor is to be designed with a voltage rating 1 kV using a material of dielectric constant 3 and 4ickeclric strength about 10 7 Vm -1 . For safety we would like the field never to exceed say, 10% of the dipole strength. What minimum area of the plats is required to have a capacitance of 50 pF? 12. A capacitor is charged by a 200 V supply. The supply is then disconnec- ted and the charged capacitor is connected to another uncharged 2 c apacitor. How much electrostatic energy of the first capacitor is lost in the process of attaining the steady situation? 13. How does the resistivity of (i) a conductor and (ii) a semiconductor vary with temperature? Give reason for each case 14. Define electric field intensity. Write its S. l . unit. Write the magnitude and direction of electric field intensity due to an electric dipole of length 2a at the mid- point of the tine joining the two charges. 15. Two cells of emf 1.5 V and 2 V and internal resistance 1 ohm and 2 ohm respectively are connected in parallel to pass a current in the same direction through an external resistance of 5 ohm. (i) Draw the circuit diagram. (ii) Using Kirchhoff's laws, calculate the current through each branch of the circuit and potential difference across the 5 ohm resistor. 16. On the basis of the energy band diagrams distinguish between metals, insulators and semiconductors 17. Define dielectric constant of a medium. Briefly explain why the capacitance of a parallel plate capacitor increases, oii introducing a dielectric medium between the plates 18. Explain how electron mobility changes for a good conductor when (i) the temperature of the conductor is decreased at constant potential difference and (ii) applied potential difference is doubled at constant temperature 19. 4 cells of identical emf E, internal resistance r, are connected in series to a variable resistor. The following graph shows the variation of terminal voltage of the combination with the current output:

(i) What is the emf of each cell used? (ii) For what current from the cells, does maximum power dissipation occur in the circuit? (iii) Calculate the internal resistance of each cell. 20. derive an expression for the electric field intensity at any point outside a charged spherical shell of radius R and of charge density 21. Define the term electric potential due to a point charge. Calculate the electric potential at the centre of a square of side having charges

at the four corners of the square. 22. Find the equivalent capacitance between A & B in following combination.


B A 5MF 23. (i) Draw two equipotentials due to a point charge. (ii) What is the amount of workdone in moving a 100nC charge between two points 5cm apart on an equipotential surface? 24. A cylindrical metallic wire is stretched to increase its length by 5%. Calculate the

percentage change in its resistance 25. The electric field E due to a point charge at any point near it is defined as where q is the test charge and F is the force acting on it. What is the physical significance of in this expression ? Draw the electric field lines of a point charge Q when (i) Q > 0 and (ii) Q < 0. 2 26. . Deduce an expression for the electric potential due to an electric dipole at any point on its axis. Mention one contrasting feature of electric potential of a dipole at a point as compared to that due to a single charge. 3

1. charge on the plates 2. electric field intensity between the plates 3. capacitance of the capacitor. Justify your answer in each case. 3

28. . State Kirchhoff's rules of current distribution in an electrical network 29. Write the mathematical relation for the resistivity of a material in terms of relaxation time, number density and mass and charge of charge carriers in it. Explain, using this relation, why the resistivity of a metal increases and that of a semi-conductor decreases with rise in temperature. 3
30. Two point charges of 4C and -2C are separated by 1m in air. Find a point on the linejoining them where electric potential is zero 31. Prove that the current density of a metallic conductor is directly proportional to the drift speed of electrons 32. A 10 cm long wire of uniform cross-section and 20 ohm resistance is connected in series with a 5 Volt battery along with an external resistance 480 ohm. If an unknown emf is balanced at 6 m length of the wire. Calculate (i) potential gradient along the wire, and (ii) the value of unknown emf. 33. Two capacitors with capacitances C1 and C2 are charged to potentials V1 and V2 respectively and then connected in parallel. Find an expression for the loss of energy during this process. 34. Two cells with emfs E1 , E2 and internal resistances r1 , r2 are connected in parallel. Find the equivalent emf and internal resistance of the combination.