# CURRENT ELECTRICITY (5 marks & 3 marks)

1. Define drift velocity and derive an expression for it..
2. Derive the expression I=nAevd
3. Deduce Ohm's law from elementary ideas and hence write an expression for resistance and resistivity.
4. Derive an expression for conductivity in terms of mobility
5. Explain the color coding of carbon resistors.
6. Derive an expression for the current in a circuit with external resistance R when (a) n identical cells of emf E and internal resistance r are connected in series (b) m identical cells are connected in parallel
7. State and explain Kirchoff's laws.
8. State and explain the principle of Wheatstone's principle. Deduce it uing Kirchoff's laws.
9. Describe how will you determine the resistance of a given wire using metre bridge.
10. Explain the principle of a potentiometer. Describe how will you determine (a) the ratio of emfs of two primary cells using potentiometer. (b)the internal resistance of a primary cell using potentiometer.
11. Explain the variation of resistance and resistivity with temperature and hence define temperature coefficient of resistance and resistivity.