Current electricity class-12

wheatstone bridge

Very short answer questions

1. On what conservation principle is the Kirchhoff's first law based?
2. On what conservation principle is the Kirchhoff's second law based?
3. Can Kirchhoff's be applied to both a.c. and d.c. circuits?
4. Name the device which is used to measure emf of a cell.
5. When is wheatstone bridge most sensitive?
6. When is a wheatstone bridge said to be balanced?
7. Write the dimensional formula of electrical conductivity.
8. State Kirchhoff's first law.
9. State Kirchhoff's second law.
10. Write the vector form of Ohm's law.
11. What is current density? Write its S.I. unit and dimensional formula.
12. Write the relation between electric current and drift velocity.
13. Define drift velocity.
14. Write the expression of drift velocity.
15. How many electrons constitute one coulomb charge ?
16. Write the relation between current density and drift velocity.
17. How much is the resistance of air gap ?
18. Do bends in a wire affect its resistance?
19. A potential difference V is applied across a conductor of length l. How is the drift velocity affected when V is doubled and l is halved?
20. If potential difference V across applied across a conductor is increased to 2V,how will the drift velocity of the electrons change?
21. Name two parameters which determine the resistivity of a material.
22. Give the order of magnitude of thermal velocity and drift velocity of free electrons in a conductor carrying current at room temperature.
    Ans:- 10⁵ ms⁻¹ , 1mms⁻¹
23. Draw a graph to show the variation of resistance of a metal wire as a function of its diameter, keeping length and temperature constant.
24. Sketch a graph showing the variation of resistivity of carbon with temperature.
25. Write the expression for internal resistance of a cell.
26. Write an expression for terminal P.D. in terms of emf and internal resistance of a cell.
27. There are two conductors A and B of the same material, having lengths l and 2l ; and having radii r and r/2 respectively. What is the ratio of their resistances?
28. Write the relation between a coulomb and an ampere.
29. How many joules are there in 1kWh?Two wires of equal cross sectional area, one of copper and other of manganin have the same resistance . Which one will be longer?
30. Which metal has the lowest resistivity?