Physics

Electrical Machines and Circuits

720 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

What is open circuit?

  1. A complete electrical circuit in which current can flow.

  2. An incomplete electrical circuit through which current cannot flow.

  3. The circuit in which equal amount of current passes through all the components.

  4. The circuit in which different amounts of current flows through the different appliances of a circuit.

  5. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

It is an open circuit.

Multiple choice

An electric bulb lights up only when _______.

  1. circuit is open

  2. circuit is closed

  3. when connected to proper terminal

  4. when we switch on the plug

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

When circuit is closed, then current easily passes through it and bulb will blink.

Multiple choice

For which of the following purposes is a transformer used?

  1. Conversion of DC into AC

  2. Regulation of fluctuation of voltage

  3. Measurement of flow of electricity

  4. Conversion of low voltage into high voltage and vice versa
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Correct Answer: Conversion of low voltage into high voltage and vice versa

Multiple choice

During which test of the induction motor, the reduced voltage is applied?

  1. No lead test

  2. Blocked rotor test

  3. Insulation test

  4. Resistance test
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The blocked rotor test applies reduced voltage to the motor while keeping the rotor stationary, measuring current and power to determine equivalent circuit parameters. This test is also called the locked-rotor test and helps determine starting torque characteristics.

Multiple choice

Which of the following statements is/are true?

  1. Half wave rectifier allows AC to flow continuously in one direction.

  2. Full wave rectifier allows AC to flow continuously in one direction.

  3. Rectification is done by a device known as amplifier.

  4. All of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Full wave rectifier allows AC to flow continuously in one direction.

Multiple choice

Why is the parallel electric circuit better for connecting bulbs in a house?

  1. The overall resistance of the circuit increases too much.

  2. Electrical appliance gets the same voltage.

  3. Electrical appliances have only one switch.

  4. If one electrical appliance stops working, then the others also stop working.

  5. They have a single operation.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In parallel circuits, each electrical appliance gets the same voltage as that of the power supply line.

Multiple choice

The earth-wire of a cable is connected to

  1. The outer metallic body of the appliance

  2. The fuse of the appliance

  3. The filament of the appliance

  4. Short circuitry of the appliance
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The earth wire (grounding wire) is connected to the outer metallic body of the appliance. This ensures that if any live wire accidentally touches the metal body, the current safely flows to earth through the earth wire, preventing electric shock. It is not connected to the fuse (which protects against overcurrent), the filament (the heating element), or short circuitry.

Multiple choice

During the course of power transmission the peak value of the voltage is

  1. 180 V

  2. 220 V

  3. 280 V

  4. 311 V
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For AC power transmission, the RMS voltage in India is 220V. The peak voltage (maximum instantaneous value) is √2 times the RMS value, so peak = 220 × √2 = 220 × 1.414 = 311V approximately. This peak value represents the maximum voltage reached during each cycle of the alternating current waveform. 220V is the RMS (root mean square) voltage, which is the effective DC equivalent.

Multiple choice

Alternating current is converted into direct current by a _____.

  1. transformer

  2. dynamo

  3. oscillator

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

A rectifier converts alternating current (AC) to direct current (DC) by allowing current flow in only one direction, using diodes in various configurations (half-wave, full-wave, bridge). Transformers only change AC voltage levels, dynamos generate electricity, and oscillators produce AC signals.