Current Electricity: Level A Questions
Current Electricity: Level A Questions
Current Electricity: Level A Questions
LEVEL A QUESTIONS
6. Obtain an expression for the conductance in terms of number density of electrons & average
collision time. (2)
11. Give expressions for the equivalent resistance in the series & parallel combination of three
resistances. (1)
13. Give the expression for the equivalent emf when cells are connected in series. (1)
14. Write the expression for the terminal voltage when two cells ofemf E1& E2 are connected in
parallel. (1)
16. Explain the principle of Wheatstone bridge with the help of a circuit diagram. .(2)
17. What is the principle on which metre bridge works?With the help of a circuit diagram
explain how an unknown resistance can be measured by using a metre bridge.
(2)
18. Give the principle of potentiometer. (1)
19. Explain the procedure with the help of a circuit diagram for comparing the emfs of the two
cells using potentiometer. (3)
20. Explain the procedure with the help of a circuit diagram for determining the internal
resistance of a primary cell using potentiometer. (3)
LEVELB QUESTIONS
5. Two wires of equal length, one of copper & the other of managing have same
resistance.Which one is thicker? (1)
6. A copper wire of resistivity ρ is stretched to reduce its diameter to half. What will be its new
resistivity? (1)
9. Though the drift velocity of electrons is very small, yet an electric bulb lights up almost
instantly when switched on. Why? (2)
10. If a current of one ampere flows through a conductor ,find the number of electrons passing
through the wire in 1.6 seconds. (1)
11. Of metals &alloys ,which has largest value of temperature coefficient of resistance? (1)
12.For a carbon resistor of 47kΩ write the sequence of colours on its rings.(1)
13. If the potential difference across a conductor is doubled ,how will it affect the drift velocity
of the electrons? (1)
14. Two electric bulbs A & B are marked 220V,60W and 220V,100W respectively. Which one
of the two has greater resistance? (2)
15. The voltage V versus current I graph for a parallel & series combination of two metallic
resistors is shown. Which graph shows the parallel combination? Justify your answer. (2)
V A
I
16. When ‘n’ identical resistors ,each of resistance R are put in series ,effective resistance is X
ohm & when they are connected in parallel the effective resistance is Y ohm. Obtain a relation
connecting X,Y& R. (2)
17. A p.d ‘V’ is applied across the ends of a conductor of length ‘L’ & diameter ‘D’. How are
the electric field E and the resistance R of the conductor are affected when:
18.A steady current flows through a metallic conductor of non uniform cross section.Which of
these quantities is constant along the conductor?
19. Three bulbs of rating 40,60& 100 W are designed to work on 220V mains.Which bulb will
glow most brightly if they are connected in series across the mains? (2)
20. Why do we prefer potentiometer for measuring emf of a cell rather than a voltmeter? (1)
21. Why should the emf of a driver cell in a potentiometer be more than the emf of a cell which
is to be determined? (1)
22.When is a potentiometer said to be more sensitive?How can its sensitivity be increased? (2)
23. Why is it advised to obtain a null point in the middle of the metre bridge wire? (1)
24.State Kirchoff’s laws of an electrical network. Using Kirchoff’s laws, calculate the potential
difference across the 8 ohm resistor.
25.A metre bridge, the balance point is found to be at 39.5 cm from the end A, when the resistor
Y is of 12.5 ohm. Determine the resistance of X. Why are the connections between resistors in a
metre bridge made of thick copper strips? What happens if the galvanometer and cell are
interchanged at the balance point of the bridge? Would the galvanometer show any current?
LEVELC QUESTIONS
3. In the given network, find the values of the currents, I1, I2 and I3. (3)
(3)
5. A wire of resistance 4R is bent in the form of a circle. What is the effective resistance between
the ends of the diameter? (1)
6.A given copper wire is stretched to reduce its diameter to half of its previous value.What is its
new resistance? (2)
7.4 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.