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

TTL with which output can be used for wired connection?

  1. Totem pole output

  2. Open collector output

  3. Active pull up

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

Open collector output TTL can be used for wired-AND (also called wired-OR for negative logic) connections. Multiple open collector outputs can be connected together with a single external pull-up resistor, implementing the AND function. Totem pole outputs cannot be wired together due to potential short circuits.

Multiple choice

An electric transformer caught fire due to an overload in current. You will

  1. call the police

  2. call the electricity board

  3. try to put it off by spraying water

  4. try to disconnect the high tension wires
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

It is too hazardous to disconnect the wires. Spraying water on the wires is also very dangerous. Calling the police is also not going to help the situation. The best option is to call the electricity board since they know how to handle the situation.

Multiple choice

A transformer is used to

  1. increase DC voltage

  2. increase or decrease AC voltage

  3. decrease DC voltage

  4. convert DC into AC
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Transformers work on the principle of electromagnetic induction, which requires a changing magnetic field. This is why transformers only function with alternating current (AC), allowing voltage to be stepped up or down. DC voltage cannot be transformed directly - it requires electronic converters.

Multiple choice

The voltage of electricity used in factories is

  1. 220 volts

  2. 440 volts

  3. 120 volts

  4. 240 volts
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Industrial electrical systems typically operate at 440 volts, which is higher than the standard 220V used in residential settings. This higher voltage efficiently powers heavy machinery and equipment.

Multiple choice

The rating of an electric lamp is 110 V. To use it on 220 V, one will have to use which one of the following?

  1. Transistor

  2. Resistor

  3. Transformer

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

To operate a 110V lamp on 220V mains, a resistor must be added in series to drop the excess voltage. Using P = V²/R, the lamp's resistance is fixed, so adding external resistance limits current to safe levels. A transformer would be more efficient but wasn't the expected answer.

Multiple choice

The constant power loss of a transformer is given by

  1. copper loss

  2. copper and eddy current losses

  3. eddy current and hysteresis losses

  4. copper loss, eddy current loss and hysteresis loss

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

Eddy current and hysteresis losses are constant losses.

Multiple choice

The instrument used to convert AC current into DC current is

  1. motor

  2. oscillator

  3. rectifier

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

A rectifier converts alternating current (AC) to direct current (DC) by allowing current flow in only one direction. This is essential for powering DC devices from AC mains and is found in all power supplies and battery chargers.