Basic Electrical Engineering

31. As the spacing between plates in a capacitor is made smaller

  1. The capacitance increases
  2. The capacitance decreases
  3. The capacitance does not change
  4. The resistance increases

Correct answer: (A)
The capacitance increases

32. At lagging loads, armature reaction in an alternator is

  1. cross-magnetising
  2. demagnetising
  3. non-effective
  4. magnetising

Correct answer: (D)
magnetising

33. At the exact moment a 60Hz ac sine wave is at its positive peak voltage, the instantaneous rate of change in the voltage is

  1. Large and positive
  2. Small and negative
  3. Large and negative
  4. Small and negative
  5. Zero

Correct answer: (E)
Zero

34. Capacitance acts to store electrical energy as

  1. Current
  2. Voltage
  3. A magnetic field
  4. An electric field

Correct answer: (D)
An electric field

35. Cells are connected in parallel to

  1. Increase the available voltage
  2. Reduce the cost of wiring
  3. Increase the available current
  4. Reduce the time required to fully charge them after use

Correct answer: (C)
Increase the available current

36. If 120°C of charge passes through an electric conductor in 60 sec, the current in the conductor is

  1. 0.5A
  2. 2A
  3. 3.33mA
  4. 0.3mA

Correct answer: (B)
2A

37. If a 175V dc source were connected in series with the utility mains from a standard wall outlet, the result would be

  1. Smooth dc at a constant voltage
  2. Pure ac with equal peak voltages
  3. Ac with one peak voltage greater than the other
  4. Fluctuating dc

Correct answer: (D)
Fluctuating dc

38. If a capacitor has a negative temperature coefficient then

  1. Its capacitance decreases as the temperature rises
  2. Its capacitance increases as the temperature rises
  3. Its capacitance does not change with temperature
  4. It will not work if the temperature is below freezing

Correct answer: (A)
Its capacitance decreases as the temperature rises

39. If all other factors are kept constant, the inductance of the air-core coil is not affected by

  1. The frequency
  2. The number of turns
  3. The diameter of the coil
  4. The length of the coil

Correct answer: (A)
The frequency

40. If two perfect sine waves have the same frequency and the same amplitude, but are in opposite phase, the composite wave

  1. Has twice the amplitude of either input wave alone
  2. Has half the amplitude of either input wave alone
  3. Is complex, but has the same frequency as the originals.
  4. Has zero amplitude ( that is, it does not exist) because the two input waves cancel each other out.

Correct answer: (D)
Has zero amplitude ( that is, it does not exist) because the two input waves cancel each other out.

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