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

In a series of small bulbs, one of the bulb fuses. Will the series of bulbs glow when the switch is on?

  1. The series of bulbs up till the fuse bulb will glow.

  2. The series of bulbs will glow as it is, except the fused bulb.

  3. The series of bulbs will not glow.

  4. The series of bulb just after the fused bulb, will glow.

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Yes, it is correct. Current passes through each bulb and because of the fused bulb, the circuit will be broken. Hence, the series of bulbs will not glow.

Multiple choice

The voltage of our household current supply is ________.

  1. 200 V

  2. 220 V

  3. 240 V

  4. 250 V
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In India and many countries, the standard household AC supply voltage is 220V at 50Hz. This is the RMS (Root Mean Square) voltage. Some countries use 110V or 240V, but 220V is the most common international standard outside North America.

Multiple choice

Why do we use rectifiers?

  1. To convert AC to DC

  2. To convert DC to AC

  3. To convert very high voltage to very low voltage

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

Rectifiers are circuits made of diodes and are used to convert AC to DC. 

Multiple choice

In an electric circuit, where is the fuse wire placed?

  1. Live wire

  2. Neutral wire

  3. Earth wire

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

The fuse wire must be placed in the live wire so that when it melts due to excess current, it disconnects the power supply from the appliance completely. If the fuse were in the neutral wire, the appliance would remain connected to live voltage even when the fuse blows, creating a serious shock hazard. The earth wire is for safety grounding and never carries current during normal operation. Placing the fuse in the neutral wire defeats the entire safety purpose of the fuse.

Multiple choice

Which of the following is the application of Voltage Dependent Resistors?

  1. Overvoltage protection crowbar for power supplies.

  2. To prevent massive power fluctuations.

  3. To suppress surges.

  4. Better cuts on metals and the welding of dissimilar metals without the use of a flux.

  5. Series resistors or current-regulated power supplies.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A varistor remains non-conductive as a shunt-mode device during normal operation when the voltage across it remains well below its clamping voltage, thus varistors are typically used for suppressing line voltage surges.

Multiple choice

Match the following:

 
a. Resistor 1. A non-metal that conducts electricity
b. Plug-key 2. Obstructs the flow of current
c. Connector 3. Used to join battery and terminals
d. Graphite 4. Used to close and open the circuit

  1. a - 2, b - 4, c - 3, d - 1

  2. a - 2, b - 4, c - 1, d - 3

  3. a - 4, b - 2, c - 3, d - 1

  4. a - 1, b - 4, c - 3, d - 2

  5. a - 2, b - 3, c - 4, d - 1
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is the correct option. A resistor obstructs the flow of current, plug-key is used to close and open the circuit, connector is used to join battery and terminals and graphite is a non-metal that conducts electricity.

Multiple choice

Consider the following statements: 1. In three pin switch, the pin of live wire is made bigger in size.

  1. Electricity transmitted along power lines is at very high voltages to reduce the loss of energy.

Which of the given statements is/are incorrect?

  1. Only (1)

  2. Only (2)

  3. Both (1) & (2)

  4. Neither of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Statement (i) is wrong. In three pin switch, the pin of earth wire is made bigger in size for the security reason. Statement (ii) is correct. Yes, to reduce the risk of loss of energy, electricity transmitted along power lines is at very high voltages.

Multiple choice

Which of the following statements regarding BEE (Bureau of Energy Efficiency) is/are correct? (1) The 5-star power saving label contains the information of resistance power of the electrical appliance. (2) Power labeling is mandatory for frost free refrigerator, air conditioner, tubular fluorescent lamp and distribution transformer.

  1. Only (1)

  2. Only (2)

  3. Both (1) & (2)

  4. Neither (1) nor (2)
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

(i) Statement (1) is wrong. The 5 star power saving label contains the information regarding electrical consumption, type of equipment, capacitance, etc. (ii) Statement (2) is also correct. Power rating is made mandatory for frost free refrigerator, air conditioner, tubular fluorescent lamp and distribution transformer.

Multiple choice

Consider the following statements:

  1. The fuse should be connected to neutral wire of appliance to get the protection against the electric shock.
  2. The fuse wires are used for household supply of electricity should have high melting point for safety purpose.

Which of the given statements is/are correct?

  1. Only (1)

  2. Only (2)

  3. Both (1) & (2)

  4. Neither (1) nor (2)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Statement (1) is wrong. Live wires carry current and our main purpose of using fuse is to break the circuit. A short circuit fault to earth or ground will bypass the neutral wire so, if the fuse were to be installed in the neutral wire, it would not operate.

Statement (2) is also wrong. A fuse is a device which is placed into an electrical circuit to prevent excessive current flowing under fault conditions. The fuse wires should have low melting point because on overloading, the wire forming the fuse element will heat up and melt (or blow) and interrupt the current flow thus preventing damage from excessive current to the remaining circuits.