Monday, 17 October 2016

CLASS 12 CBSE PHYSICS ELECTROSTATICS AND CURRENT ELECTRICITY ONE MARK QUESTIONS

1. Draw schematically an equipotential surface of a uniform electrostatic field along x-axis.
2. Sketch field lines due to (i) two equal positive charges near each other (ii) a dipole.
3. Name the physical quantity whose SI unit is volt/meter. Is it a scalar ora vector quantity?
4. Two point charges repel each other with a force F when placed in water of dielectric constant 81.
   What will the force between them when placed the same distance apart in air?
5. Electric dipole moment of CuSO4 molecule is 3.2 × 10–32 Cm. Find theseparation between copper
   and sulphate ions.
6. Net capacitance of three identical capacitors connected in parallel is 12microfarad. What will be    
   the net capacitance when two of them areconnected in (i) parallel (ii) series?
7. A charge q is placed at the centre of an imaginary spherical surface. What will be the electric flux
   due to this charge through any half of the sphere.
8. Draw the electric field vs distance (from the centre) graph for (i) a long charged rod having linear
   charge density λ <; 0 (ii) spherical shell of radius R and charge Q > 0.
9. Diagrammatically represent the position of a dipole in (i) stable (ii) unstable  equilibrium when
  placed in a uniform electric field.
10. A charge Q is distributed over a metal sphere of radius R. What is the electric field and electric
   potential at the centre?
11. If a body contains n1 electrons and n2 protons then what is the total charge on the body?
12. What is the total positive or negative charge present in 1 molecule of water.
13. How does the energy of dipole change when it in rotated from unstable equilibrium to stable equilibrium in a uniform electric field.
14. Write the ratio of electric field intensity due to a dipole at a point on the equatorial line to the field
   at a point at a point on the axial line, when the points are at the same distance from the centre of
   dipole.
15. Draw equipotential surface for a dipole.
16. An uncharged conductor A placed on an insulating stand is brought near a charged insulated conductor B. What happens to the charge and potential of B?
17. A point charge Q is placed at point O shown in Fig. Is the potentialdifference VA – VB positive,
   negative or zero, if Q is (i) positive (ii) negative charge.
18. An electron and proton are released from rest in a uniform electrostatic field. Which of them will
    have larger acceleration?
19. In an uniform electric field of strength E, a charged particle Q moves point A to point B in the
    direction of the field and back from B to A. Calculate the ratio of the work done by the electric
     field     in taking the charge particle from A to B and from B to A.
20. If a dipole of charge 2μC is placed inside a sphere of radius 2m, what is the net flux linked with
   the sphere.
21. Four charges + q, –q, +q, –q are placed as shown in the figure. What is the work done in
    bringing a test charge from ∞ to point 0.
22. Calculate number of electric field lines orignating from one coulomb charge.
23. If the metallic conductor shown in the figure is continuously charged from which of the points
    A,B,C or D does the charge leak first. Justify.
24. What is dielectric strength? Write the value of dielectric strength of air.

25. Two charge –q and +q are located at points A (0, 0, –a) and B(0, 0, +a). How much work is done
     in moving a test charge from point (b, 0, 0) to Q (–b, 0, 0)?
26. If an electron is accelerated by a Potential difference of 1 Volt, Calculate the gain in energy in
    Joule and electron volt.

27. Draw schematically the equipotential surface corresponding to a field that uniformly increases in
    magnitude but remains in a constant (say z) direction.
28. Without referring to the formula C = ε0A/d. Explain why the capacitance of a parallel plate
     capacitor reduces on increasing the separation between the plates?
29.Draw field lines to show the position of null point for two charges + Q1 and –Q2 when magnitude
   of Q1 > Q2 and mark the position of null point.
30. How does the relaxation time of electron in the conductor change when temperature of the conductor decreases.
31. Sketch a graph showing variation of resistivity with temperature of (i) Copper (ii) Carbon.
32. The emf of the driver cell (Auxillary battery) in the potentiometer experiment should be greater than emf of the cell to be determined. Why?
34. You are required to select a carbon resistor of resistance 47kΩ ± 10% from a large collection. What should be the sequence of color bands used to code it?
36. Two wire one of copper and other of manganin have same resistance  and equal length. Which wire is thicker?
37.Why is the potentiometer preferred to a voltmeter for measuring emf of a cell?
38. How can a given 4 wires potentiometer be made more sensitive?
39. Why is copper not used for making potentiometer wires?
40. A copper wire of resistance R is uniformally stretched till its length is increased to n times its original length. What will be its new resistance?
41. What is the largest voltage that can be safely put across a resistor marked 196Ω, 1W?
42. When does the terminal voltage of a cell become (i) greater than its emf (ii) less than its emf?

43.A car battery is of 12V. Eight dry cells of 1.5 V connected in series also give 12V, but such a
   combination is not used to start a car. Why?
44. Two electric lamps A and B marked 220V, 100W and 220V, 60W respectively. Which of the two
     lamps has higher resistance?
45. Resistors of high value are made up of carbon. Why ?
46. A 16Ω thick wire is stretched so that its length becomes two times.Assuming there is no change in density on stretching. Calculate the resistance of new wire.
47. State the Condition under which the terminal potential difference across
a battery and its emf are equal.

48. State the Condition for maximum current to be drawn from a Cell.