Sunday, 6 September 2015


Q1: A charge of 150 C flows through a wire in one minute. Find the electric current flowing through it.

Q2: The resistance of a wire of 0.01 cm radius is 10 Ω. If the resistivity of the material of the wire is 50 × 10-8 Ω­m, find the length of wire.

Q3: A circuit has line a line of 5A. How many lamps of rating 40W; 220V can simultaneously run on this line safely?

Q4: Show four different ways in which four resistors of r Ω each may be connected in a circuit. In which case is the equivalent resistance of the combination. (i) maximum (ii) minimum 

Q5: Amit lives in Delhi. He is much concerned about the increasing electricity bill of his house. He took some steps to save electricity and suceeded in doing so.
(i)                  Mention any two steps that Amit might have taken to save electricity.
(ii)                 (ii) Amit fulfilled his duty towards the environment by saving electricity. How? (iii) Which alternative source of energy would you suggest Amit to use? 

Q6: What is meant by resistance of a conductor? Name and define its SI unit? List the factors on which the resistance of a conductor depends. How is the resistance of a wire affected if: (i) its length is doubled, (ii) its radius is doubled? 

Q7: (a) Draw magnetic field lines of a bar magnet. "Two magnetic field linesnever interact with each other". Why? (b) An electric oven of 1.5 kW is operated in a domestic circuit (220V) that has a current rating of 5A. What result do you expect in this case? Explain. 

Q8: A student verifying Ohm's law computed the value of resistance of a resistor for each set of observation.
However the values of the resistor were slightly different from the actual value. Is his experiment wrong? Justify
your answer. 

9. Write any one method to induce current in a coil.

10 . The potential difference between the two terminals of an electric iron is 220 V and the current flowing through its element is 5.0 A. Calculate the resistance and wattage of the electric iron.

11 . Give reason for the following: (i) Why are copper and aluminum wires used as connecting wires? (ii) Why is tungsten used for filaments of electric lamps? (iii) Why is lead tin alloy used for fuse wires ?
12. An electric heater is used on 220 V supply and takes a current of 5 A. What is its power ? Calculate the per hour cost of using the heater if 1 unit costs. Rs. 6.0.

13 . A student fixes a sheet of white paper on a drawing board. He places a bar magnet in the centre of it.
He sprinkles some iron filings uniformly around the bar magnet. Then he taps the board gently. Now
answer the following questions :
(i) What does the student observe ? Draw a diagram to illustrate your answer.
(ii) Why do the iron filings arrange in such a pattern ?
(iii) What does the crowding of the iron filings at the ends of the magnet indicate ?

14 . What is meant by electric circuit ? What is done in order to have continuous flow of electric charge froma point A to another point B in an electric circuit ? Write the relation between coulomb and ampere.
Calculate the number of electrons passing per second through a conductor to produce a current of one ampere. (Charge on electron = 1.6 x 10 - 19 coulomb)

15. What is meant by an electric circuit?

16. Name, State and explain with the help of a diagram the rule to find the direction of magnetic field around a straight conductor carrying current.
17. List two safety measures commonly used in electric circuits. Explain the main function of each.
24. (a) How does the resistance of a wire change when- (i) Its length is tripled? (ii) Its radius is tripled?
(iii)Its material is changed to one whose resistivity is three times?
(b) List two reasons why nichrome is used for making heatingelement of electrical appliances
18.State how the magnetic field produced by a straight current carrying conductor at a point depends on (a) current through the conductor (b) distance of point from conductor.

19.Two lamps, one is rated 100 W at 200 V and the other 60 W at 220 V, are connected in parallel to a 220 V supply. Find the current drawn from the supply line.

20.(a) Fuse acts like a watchman in an electric circuit. Justify this statement. (b) Mention the usual current rating of the fuse wire in the line to (a) lights and fans (b) appliance of 2kw or more power.

21.(a) A fuse wire melts at 5A . If it is desired that the fuse wire of same material melt at 10 A, then whether the new fuse wire should be of smaller or larger radius than the earlier one ? Give reasons for your answer.
 (b) If the radius of a current carrying conductor is halved, how does current through it change ?

22.Define resistance of a conductor. State the factors on which resistance of a conductor depends. Name the device which is often used to change the resistance without changing the voltage source in an electric circuit. Calculate the resistance of 50 m length of wire of cross sectional area  of 0.01 square mm and of resistivity 5X10-8Ω.m