Electricity

MCQs Part 5

21. Twelve equal resistors, each of resistance R, are connected to form a skeleton cube. Then the equivalent resistance taken between two diagonally opposite corners is

  1. R
  2. 12R
  3. 5R/6
  4. 7R/12

22. The resistance of a metallic wire becomes 8 times when

  1. length is doubled
  2. length is tripled
  3. length is doubled and radius is halved
  4. length is halved and radius is doubled

23. The value of current I in the given circuit is

  1. 3A
  2. 13 A
  3. 23 A
  4. -3A

24. There is a current of 1.344 amp in a copper wire whose area of cross-section normal to the length of the wire is 1 mm2. If the number of free electron per cm3 is 8.4 × 1022, then the drift velocity would be

  1. 1.0 mm per sec.
  2. 1.0 meter per sec.
  3. 0.1 mm per sec.
  4. 0.01 mm per sec.

25. In the following figure, the value of resistor to be connected between C and D so that the resistance of the entire circuit between A and B does not change with the number of elementary sets used is

  1. R
  3. 3R

Answer: 21. (d), 22. (b), 23. (a), 24. (c), 25. (a)

26. In the following figure, the resistance of the galvanometer G is 50 ohm. Of the following alternative in which case are the currents arranged strictly in the order of decreasing magnitudes with the larger coming earlier.

  1. I, I1, Ig, I2
  2. I, Ig, I1, I2
  3. I, I2, I1, Ig
  4. Ig, I1, I2, I

27. Five resistance have been connected as shown in the figure. The effective resistance between A and B is

28. When a resistance of 2 ohm is connected across the terminals of a cell, the current is 0.5 amp. When the resistance is increased to 5 ohm, the current is 0.25 amp. The e.m.f. of the cell is

  1. 1.0 volt
  2. 2.0 volt
  3. 1.5 volt
  4. 2.5 volt

29. Three copper wires have lengths and cross sectional areas as: (l, A), (2l, A/2) and

Resistance is minimum in

  1. wire of cross-sectional area A/2
  2. wire of cross-sectional area A
  3. wire of cross-sectional area 2A
  4. same in all the three cases

30. Two wires of same metal have same length but are joined in series. The resistance of the thicker wire is . The total resistance of the combination will be

  1. (5/2)W
  2. (40/3)W
  3. 40W
  4. 100 W

Answer: 26. (b), 27. (b), 28. (b), 29. (c), 30. (c)

31. In an experiment to measure the interal resistance of a cell by a potentiometer, it is found when the cell is shunted by a 5 W resistance and at a length of 3 m when the cell is shunted by a 10 W resistance. The internal resistance of the cell is then

  1. 1.5 W
  2. 10 W
  3. 15 W
  4. 1 W

32. The current in the primary circuit of a potentiometer wire is 0.5 A, r for the wire is 4 × 10_7 W_m and area of cross-section of wire is 8 × 10_6 m2. The potential gradient in the wire would be

  1. 25 mV/metre
  2. 2.5 mV/metre
  3. 25 V/metre
  4. 10 V/metre

33. A cell when balanced with potentiometre gave a balance length of 50 cm. Then a 4.5 W external resistance is introduced in the circuit. Now it is balanced on 45 cm. The internal resistance of the cell is

  1. 0.25 W
  2. 0.5 W
  3. 1.0 W
  4. 1.5 W

34. There is no current in a 2W resistance; then the equivalent resistance of the given circuit is

  1. 10W
  2. 20W
  3. (13/7)W
  4. 4W

35. In the circuit shown in the following figure, the potential difference between points A and B will be

  1. (8/9) volt
  2. (4/3) volt
  3. (2/3) volt
  4. 2 volt

Answer: 31. (b), 32. (d), 33. (c), 34. (a), 35. (b)

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