PHYSICS - CURRENT ELECTRICITY - CLASS 12 - ASSIGNMENT 3

 PHYSICS

ASSIGNMENT 3

CLASS 12

CURRENT ELECTRICITY


1. What is current electricity?


2. Define electric current.  Give its SI unit.


3. Distinguish between conventional and electronic current.


4. Define emf of a battery.  When is the emf of a battery equal to the potential difference between its terminals?


5. Is electric current a scalar or vector quantity?


6. Distinguish between electromotive force and potential difference.


7. How is the flow of electric current maintained in an electric circuit?


8. State Ohm's law.


9. Define resistance and state its SI unit.


10. Explain how we can measure the resistance of a wire.


11. What are the factors on which the resistance of a conductor depend?


12. Define resistivity and state its SI unit.


13. Define the following and also write their SI units:

a. current density

b. conductance

c. conductivity


14. (i) Which metal has the lowest resistivity?

      (ii) What is the order of resistivity of an insulator?


15. (i) What is the order of resistivity of conductor?

      (ii) How much is the resistance of a closed plug key?


16. Name two materials whose resistivity decreases with the rise of temperature.


17. Derive vector form of Ohm's law.


18. Define drift velocity.


19. Derive relation between electric current and drift velocity. Hence deduce Ohm's law.


20. Write the expression for resistivity in terms of number density of free electrons and relaxation time.


21. Name two parameters which determine the resistivity of a material.


22. What causes resistance in a conductor?


23. Explain the cause of instantaneous current in an electric circuit.


24. Define mobility of charge carrier.


25. What is a non ohmic device? State one example.


26. Give an example of non ohmic device which shows up negative resistance.


27. What is a linear resistor?


28. Explain the variation of resistivity of metals, semiconductors, insulators and electrolytes with the change in temperature.


29. Mention the uses of alloys in making standard resistors.


30. What is Meissner effect?


31. State the conditions under which Ohm's law is not obeyed in a conductor.


32. What is meant by equivalent resistance of  a combination of resistances?


33. Find an expression for the equivalent resistance of a number of resistances connected in series.


34. Find the equivalent resistance of a number of resistances connected in parallel.


35. what is internal resistance of a cell? On what factors does it depend?


36. Derive a relation between the internal resistance, emf and terminal potential difference of a cell.


37. Obtain an expression for the heat developed in a resistor by the passage of an electric current through it. Hence state Joule's law of heating.


38. Define electric power and write its SI unit.


39. State Kirchhoff's laws for electrical circuits. Also state the sign conventions used.


40. What is a Wheatstone bridge?  When is the bridge said to be balanced?  Apply Kirchhoff's laws to derive the balance condition of the Wheatstone bridge.


41. Write the advantages of Wheatstone bridge method.


42. Define sensitivity of a Wheatstone bridge.  On what factors does it depend?

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