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

The device which converts AC to DC is

  1. Oscillator

  2. Amplifier

  3. Rectifier

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

A rectifier uses diodes to convert alternating current (AC) to direct current (DC) by allowing current flow in only one direction. Oscillators generate AC signals, amplifiers increase signal amplitude, and neither performs conversion.

Multiple choice

When the main switch of the house is put off it disconnects the

  1. Live wire only

  2. Live wire and the earth wire

  3. Live wire and the neutral wire

  4. Earth wire and the neutral wire
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The main switch disconnects only the live (phase) wire to cut off power supply. The neutral wire remains connected to ground. The earth wire is a safety connection and is also not disconnected by the main switch. This prevents current flow while maintaining safety grounding.

Multiple choice

Directions: In the following question, find out the alternative which will replace the blank.

Resistance: Ohm :: Power: _________

  1. Energy

  2. Force

  3. Power station

  4. Watt

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The relationship is Physical Quantity: Its SI Unit. Resistance is measured in Ohms. Similarly, Power is measured in Watts. This tests knowledge of SI units in physics. Energy (Joule), Force (Newton), and Power station (place, not unit) are incorrect.

Multiple choice

Which device is used to limit the current in an electric circuit?

  1. Grid

  2. Fuse

  3. Hub

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

A fuse is a safety device that limits current by melting and breaking the circuit when current exceeds its rated capacity. Grids, hubs, and conductors are circuit components that do not provide current limiting protection.

Multiple choice

A DC voltmeter is capable of measuring a maximum of 300 volts. If it is used to measure the voltage across a device operating at 220-volts AC supply, the reading of the voltmeter will be- Which of these incidents caused alarm among the British rules?

  1. 300 volts

  2. 200 volts

  3. 110 volts

  4. 0 volts
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A DC voltmeter measures the average value of a voltage signal. Since a standard AC supply is a symmetric sine wave, its average value over a cycle is zero, resulting in a zero reading on a DC meter.

Multiple choice

A fuse wire is used in an electric circuit to:

  1. minimize loss of electric energy in transmission

  2. maintain constant voltage level

  3. prevent excessive current from passing through the circuit

  4. prevent heating of electric wire

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A fuse is a safety device consisting of a strip of wire that melts and breaks an electric circuit if the current exceeds a safe level. This prevents damage to the electrical appliances and the wiring from overheating or fire.

Multiple choice

A device which is used to limit the current in an electric circuit is called a

  1. grid

  2. fuse

  3. hub

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

A fuse is a safety device designed to protect an electrical circuit from excessive current. It contains a wire that melts and breaks the circuit if the current becomes too high, thereby limiting the flow and preventing damage or fire. A conductor, by contrast, allows current to flow easily.

Multiple choice

Who gave 'Ohm's law?

  1. T.E Ohm

  2. G.S Ohm

  3. F.Ohm

  4. S.Ohm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ohm's Law, which describes the relationship between voltage, current, and resistance, is named after the German physicist Georg Simon Ohm.

Multiple choice

Which of the following statements is/are not true?

(a) Electricity flow in open circuit (b) Electricity flow in closed circuit (c) Electricity flow when the switch is open (d) Electricity flow when the switch is closed

  1. Both (a) and (c)

  2. Both (c) and (d)

  3. Both (b) and (d)

  4. Both (a) and (d)

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

This is the correct answer. Correct options are (a) Electricity flows in a closed circuit and (c) Electricity flows when the switch is closed.

Multiple choice

In which of the following cases an electrical circuit may be broken?

(a) Circuit is made up of cotton threads. (b) Circuit is made up of copper wires. (c) Current flows from positive to negative. (d) Current flows from negative to positive.

  1. Both (b) and (c)

  2. Both (a) and (d)

  3. Both (a) and (c)

  4. Both (b) and (d)

  5. -
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This is the correct answer. Circuit is broken when it is made up of cotton threads, as cotton is a bad conductor of electricity. Current cannot flow from negative to positive, so the circuit is broken.