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## Tuesday, May 3, 2011

### NUMERICAL - Electricity & its effects For (Class X)

NUMERICAL - Electricity & its effects For (Class X)

1. Calculate the number of electrons constituting one coulomb of charge per second through any cross section of a conductor.

2. How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V ?

3. How much energy is given to each coulomb of charge passing through a 6 V battery ?

4. Calculate the work done in moving a charge of 5 Coulombs from a point at a potential of 210 Volts to another point at 240 Volts.

5. When a particle of charge 10 µC is brought from infinity to a point P, 2.0 mJ work is done by the external forces. What is the potential at P ?

6. How many electrons pass through a lamp in one minute if the current be 200 mA?

7. Calculate the current supplied by a cell if the amount of charge passing through the cell in 4 seconds is 12 C ?

8. A 2 Volt cell is connected to a 1 Ω resistor. How many electrons come out of the negative terminal of the cell in 2 minutes ?

09. a) How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 Ω ?
b) How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100 Ω ?

10. The potential difference between the terminals of an electric heater is 60 Volts when it draws a current of 4 Ampere from a source. What current will the heater draw if the potential difference is increased to 120 Volt.

11. A torch bulb when cold has 1Ω resistance. It draws a current of 0.3 Ampere when glowing from a source of 3 V. Calculate the resistance of the bulb when glowing and explain the reason for the difference in resistance.

12. A current of 0.2 Ampere flows through a conductor of resistance 4.5 Ω. Calculate the potential difference at the ends of the conductor.

13. A resistance of 6 ohms is connected in series with another resistance of 4 ohms. A potential difference of 20 volts is applied across the combination. Calculate the current through the circuit and potential difference across the 6 ohm resistance.

14. Resistors R1, R2, R3 having values 5Ω, 10 Ω, 30 Ω respectively are connected in parallel across a battery of 12 Volts. Calculate (i) Current through each resistor (ii) otal current. (iii) Total resistance.

15. An electric lamp of 100 Ω, a toaster of resistance 50 Ω , and a water filter of resistance 500 Ω are connected in parallel to a 220 Volt source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it ?

16. How can three resistances of 2Ω, 3Ω & 6Ω be connected to give the total resistance of                   a) 4Ω b) 1 Ω

17. An electric lamp, whose resistance is 20 Ω, and a conductor of 4 Ω resistance are connected to a 6 V battery . Calculate
(a) The total resistance of the circuit,
(b) The current through the circuit, and
(c) The potential difference across the electric lamp and conductor.

18. a) Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a 5 Ω resistor, an 8 Ω resistor, and a 12 Ω resistor, and a plug key, all connected in series.

b) Redraw the circuit of above, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the potential difference across the 12 Ω resistor. What would be the readings in the ammeter and the voltmeter.

19. Judge the equivalent resistance when the following are connected in parallel – (a) 1 Ω and 106 Ω (b) 1 Ω and 103 Ω, and 106 Ω.

20. What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω?
21. A piece of wire having a resistance R is cut into four equal parts.  (i) How will the resistance of each part of the wire will compare with the original resistance?
(ii) If the four parts of the wire are placed in parallel, how will the resistance of the combination compare with the resistance of the original wire?

22. When two resistances R1 & R2 are connected in parallel, the net resistance is 3Ω. When connected in series, its value is 16Ω. Calculate the value of R1 & R2 .