Questions and answers for exam Preparation

MCQs

Total Questions : 480 | Page 5 of 48 pages

Question 41. Which one of the following statements best describes magnetic hysteresis?

Hysteresis is the amount of magnetic flux that is not confined to the core material of an electromagnet
Hysteresis is most apparent when a steady amount of current is lowing through the coil of an electromagnet
Hysteresis is most apparent when the current through the coil of an electromagnet changes frequently
Hysteresis is most apparent when the core material is saturated
None of the above

Discuss Question

Answer: Option C. -> Hysteresis is most apparent when the current through the coil of an electromagnet changes frequently

Question 42. Which one of the following phrases best describes residual magnetism?

Magnetism that remains in the core of an electromagnet after the current through the coil is turned off
The force of attraction between the poles of a permanent and temporary magnetic field
The amount of magnetic flux that is not confined to the core material of an electromagnet
The circular magnetic field that surrounds a conductor carrying a current
None of the above

Discuss Question

Answer: Option A. -> Magnetism that remains in the core of an electromagnet after the current through the coil is turned off

Question 43. A transformer has a primary voltage of 120 V rms and a secondary voltage of 25 V rms. If the secondary current is 1A rms, what is the primary current?

7.8 mA
208 mA
200 mA
300 mA
None of the above

Discuss Question

Answer: Option B. -> 208 mA

Question 44. Household light bulbs have a given power rating, and they operate at 120 V. Which one of the following equations most directly provides the current rating of these light bulbs?

P = I2R
P = IE
P = E2/R
I = P/E
None of the above

Discuss Question

Answer: Option D. -> I = P/E

Question 45. Which one of the following phrases most accurately describes a purely inductive circuit?

Resistances provide the only opposition to current flow
Inductive reactance provides the only opposition to current flow
Combinations of resistance and inductive reactance provide any opposition to current flow
The ac voltage lags the current by 90 degree
None of the above

Discuss Question

Answer: Option B. -> Inductive reactance provides the only opposition to current flow

Question 46. The knee voltage of a diode is approximately equal to the

Applied voltage
Barrier potential
Breakdown voltage
Forward voltage
None of the above

Discuss Question

Answer: Option B. -> Barrier potential

Question 47. A zener regulator has an input voltage from 15 to 20 V and a load current from 5 to 20 mA. If the zener voltage is 6.8 V, what value should the series resistor have?

310 Ohm
400 Ohm
410 Ohm
550 Ohm
None of the above

Discuss Question

Answer: Option C. -> 410 Ohm

Question 48. The rms value of a sine waveform is:

the number of cycles completed in one second
the time required to complete one full cycle
equal to 0.707 times the peak amplitude
equal to 1.41 times the peak amplitude
None of the above

Discuss Question

Answer: Option C. -> equal to 0.707 times the peak amplitude

Question 49. Which one of the following is a direct statement of Ohm's law?

The voltage drop across a resistance is proportional to the value of resistance and the amount of current flowing through it
The total resistance of a parallel circuit is less than the value of the smallest resistance
The algebraic sum of voltages in a loop is equal to zero
The algebraic sum of currents entering and leaving a point is equal to zero
None of the above

Discuss Question

Answer: Option A. -> The voltage drop across a resistance is proportional to the value of resistance and the amount of current flowing through it

Question 50. A high-pass filter: