Electricity

MCQs Part 4

1. Electric current is due to drift of electrons in

  1. metallic conductors
  2. semiconductors
  3. both
  4. none of the above

2. 10,000 alpha particles per minute are passing through a straight tube of radius r. The resulting electric current is approximately

  1. 0.5 × 10_16 amp
  2. 2 × 1012 amp
  3. 0.5 × 1012 amp
  4. 2 × 10_12 amp

3. In the Bohr's model of hydrogen atom the electron moves around the nucleus in a circular orbit of radius 5 × 10_11 m with time period 1.5 × 10_16 sec. The current associated with the electron motion is

  1. zero
  2. 1.6 × 10_19 amp
  3. 0.17 amp
  4. 1.07 × 10_3 amp

4. The temperature of a metal wire rises when an electric current passes through it because

  1. collision of metal atoms with each other releases heat energy
  2. collision of conduction electrons with each other release heat energy
  3. when the coduction electron fall from higher energy level to lower energy level heat energy is released
  4. collision of conduction electrons with the atoms of metal give them energy which appears as heat

5. Unit of resistance is

  1. Volt/amp
  2. Volt2/amp
  3. Volt/amp2
  4. Volt

Answer: 1. (b), 2. (b), 3. (d), 4. (c), 5.(c)

6. The resistivity of a wire depends on its

  1. length
  2. area of cross-section
  3. shape
  4. material

7. The resistor R1 dissipates power P when connected to a generator. If a resistor R2 is inserted in series with R1, the power dissipated by R1

  1. increases
  2. decreases
  3. remains the same
  4. may decrease or increase depending on the values of R1 and R2

8. The e.m.f. of the Daniel cell is

  1. 0.56 Volt
  2. 1.12 Volt
  3. 2.56 Volt
  4. 3.12 Volt

9. The maximum current that flows in the fuse wire, before it blows out, varies with the radius r as

  1. r3/2
  2. r
  3. r2/3
  4. r1/2

Answer: 6. (c), 7. (b), 8. (b), 9. (b), 10. (c)

10. Formula for resistivity is

  1. RA/l
  2. l/AR
  3. Rl/A
  4. None of these

11. A wire of resistance R is cut into n equal parts. These parts are then connected in parallel. The equivalent resistance of the combination will be

  1. nR
  2. R/n
  3. n/R
  4. R/n2

12. Kirchhoff's first law is based on the law of conservation of

  1. charge
  2. energy
  3. momentum
  4. sum of mass and energy

13. There is a current of 4.8 ampere in a conductor. The number of electrons that cross any section normal to the direction of flow per second, is

  1. 1019
  2. 2 × 1019
  3. 3 × 1019
  4. 7.68 × 1020

14. A piece of copper wire is cut into ten equal parts. These parts are connected in parallel. The joint resistance of the parallel combination will be equal to the original resistance of uncut wire, mulitplied by a factor of

  1. 0.01
  2. 0.1
  3. 10
  4. 100

15. If R1 and R2 are respectively the filament resistances of a 200 watt bulb and a 100 watt bluld designed to operate on the same voltage

  1. R1 is two times R2
  2. R2 is two times R1
  3. R2 is four times R1
  4. R1 is four times R2

Answer: 11. (c), 12. (c), 13. (c), 14. (b), 15. (d)

16. A cell of e.m.f. E is connected across a resistance r. The potential difference between the terminals of the cell is found to be V. The internal resistance of the cell must be

  4. (E _ V)r

17. Kirchhoff's first law at a junction deals with the conservation of

  1. charge
  2. energy
  3. momentum
  4. angular momentum

18. A piece of wire of resistance R is cut into n equal parts. These parts are then connected in parallel. If the equivalent resistance of the parallel combination is R', then (R/R') is

  1. 1/1
  2. n/1
  3. n2/1
  4. 1/n

19. Three equal resistors, each equal to R are connected as shown in the adjoining figure; then the equivalent resistance between pioint A and B is

  1. R
  2. 3R
  3. R/3
  4. 2R/3

20. In the adjoining network of resistors, each of resistance R ohm, the equivalent resistance between points A and B is

  1. 5R
  2. 2R/3
  3. R
  4. R/2

Answer: 16. (b), 17. (c), 18. (c), 19. (a), 20. (c)

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