Physics

Electrical Machines and Circuits

754 Questions

Electrical machines and circuits involve the principles of alternating and direct current, transformers, diodes, and power consumption. These concepts are essential for engineering and technical exams. Review these practice questions to test your knowledge of circuit analysis.

Transformers and impedanceAlternating and direct currentCircuit components and diodesPower consumption calculations

Electrical Machines and Circuits Questions

Multiple choice

Which of the following statements is/are incorrect?

a. Current does not flow if a circuit is complete. b. An electric circuit is opened when the switch is in the ‘ON’ position. c. A bulb will glow only when the electric circuit is open.

  1. a only

  2. b only

  3. c only

  4. b and c

  5. a, b and c
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

This is the correct answer as all statements are incorrect. Current flows only if a circuit is complete. An electric circuit is closed when the switch is in the ‘ON’ position. A bulb will glow only when the electric circuit is closed.

Multiple choice

Which of the following cause(s) excessive currents in electrical circuit?

  1. Overload in circuit

  2. Direct touching of wires

  3. Insulation on the wires coming off due to wear and tear

  4. Connection of many devices to a single socket

  5. All of the above
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

This is the correct option as all of the above are the reasons for excessive currents in electrical circuit.

Multiple choice

Which of the following statements is/are correct?

a. Different types of fuse are used in different types of circuits. b. These days, MCBs are used in place of fuses. c. Any wire or strip of metal can be used in place of a fuse.

  1. only a and b

  2. only b and c

  3. only a and c

  4. a, b and c

  5. only a
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is the correct answer as both statements are correct. Different types of fuse are used in different types of circuits. These days, MCBs are used in place of fuses.

Multiple choice

Which of the following statements is/are correct?

a. In the symbol of electric cell, the longer line represents the positive terminal and the thicker, shorter line represents the negative terminal. b. The heat wastage can be reduced by using CFL bulbs in place of electric bulbs. c. The ISI mark on an electrical appliance ensures that the circuit has been checked and is working properly.

  1. a only

  2. b only

  3. c only

  4. a and b

  5. a, b and c
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This is the correct answer as both these statements are correct.

Multiple choice

Sodium vapour lamps are preferred to incandescent lamp because of

  1. Higher tolerance to voltage fluctuation

  2. Higher intensity of illumination

  3. Easy installation

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Sodium vapor lamps produce nearly monochromatic yellow light (589 nm) with very high luminous efficacy - around 100-200 lumens per watt compared to 10-20 lumens per watt for incandescent lamps. This gives them much higher intensity of illumination for the same power consumption.

Multiple choice

Rectifiers are used to convert

  1. Low voltage to high voltage

  2. High voltage to low voltage

  3. D.C. to A.C.

  4. A.C. to D.C.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Rectifiers convert alternating current (A.C.) to direct current (D.C.) using diodes that allow current flow in only one direction.

Multiple choice

AC cannot be used in

  1. Amplifier

  2. Transformer

  3. Voltmeter

  4. Galvanometer
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Galvanometers measure direct current. AC would cause the needle to vibrate rapidly around zero, making reading impossible.

Multiple choice

The circuit element where the impressed voltage is always in phase with the resulting current is?

  1. An ideal resistor

  2. An ideal capacitor

  3. An ideal coil

  4. An ideal transformer
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In an ideal resistor, voltage and current are always in phase because resistors follow Ohm's Law (V = IR) without any phase shift. In an ideal capacitor, current leads voltage by 90 degrees. In an ideal coil (inductor), voltage leads current by 90 degrees. An ideal transformer has phase relationships between its primary and secondary windings.

Multiple choice

Electric current of a 100w, 220v electric bulb is _____.

  1. 2.2 A

  2. 1.1 A

  3. 0.45 A

  4. 0.22 A
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using the power formula P = VI, current I = P/V = 100W/220V = 0.4545...A ≈ 0.45A. This is the standard calculation for finding current from power and voltage ratings. Option A (2.2A) would be P/V = 484W, option B (1.1A) would be 242W, and option D (0.22A) would be 48.4W - none match the 100W rating.