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 technology

A voltage will influence current only if the circuit is:

  1. open

  2. insulated

  3. high resistance

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

Voltage can only influence current flow in a closed circuit. An open circuit has no complete path for current. Insulation prevents current flow. High resistance limits but doesn't prevent current. Only a closed circuit allows current to flow continuously.

Multiple choice technology

A basic electric circuit is made up of what components?

  1. A load, a resistor, and a conductive path for current

  2. A voltage source, a load, and a conductive path for current

  3. . A voltage source, a conductive path for current, and a battery

  4. A conductive path for current, a battery, and a copper wire
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A complete electric circuit requires three essential components: a voltage source (battery, power supply) that provides potential difference, a load (resistor, device) that consumes electrical energy, and a conductive path (wires, traces) that connects them allowing current to flow.

Multiple choice technology

The purpose of choke in tube light is ?

  1. To decrease the current

  2. To increase the current

  3. To decrease the voltage momentarily

  4. To increase the voltage momentarily
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The choke in a tube light is a ballast that creates a high voltage surge when the starter is switched on. This momentary voltage increase is necessary to ionize the gas inside the tube and start the current flow.

Multiple choice technology

Larger buildings may be supplied with a medium voltage electricity supply, and will required a substation or mini-sub. What is the main item of equipment contained in these?

  1. Transformer

  2. Transponder

  3. Transducer

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

A transformer is the primary component in a substation or mini-sub, used to step down the medium voltage (typically 11kV, 22kV, or 33kV) to the low voltage (415V/240V) needed for building distribution. Transponders are communication devices, transducers convert energy forms, and converters change AC to DC - none of these are the main equipment in distribution substations.

Multiple choice

Which cable is utilised to get power from main socket?

  1. Power cable

  2. Signal cable

  3. AC cable

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

The power cable connects electronic devices to the main power socket, supplying the necessary electrical current for operation. Signal cables transmit data signals between devices. AC cables carry alternating current but 'power cable' is the specific common term for the cable from the main socket to the device.

Multiple choice

An ideal op-amp is an ideal

  1. voltage controlled current source

  2. voltage controlled voltage source

  3. current controlled current source

  4. current controlled voltage source
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

An ideal OPAMP is an ideal voltage controlled voltage source.

Multiple choice

Voltage series feedback (also called series-shunt feedback) results in

  1. increase in both input and output impedances

  2. decrease in both input and output impedances

  3. increase in input impedance and decrease in output impedance

  4. decrease in input impedance and increase in output impedance
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In voltage series feedback amplifier, input impedance increases by factor $(1+A\beta)$ and output impedance decreases by the factor $(1+A\beta)$

$$R_{if} = R_i(1+A\beta)\\

R_{of} = \dfrac{R_0}{(1+A\beta)} $$

Multiple choice

The effect of current shunt feedback in an amplifier is to

  1. increase the input resistance and decrease the output resistance

  2. increase both input and output resistances

  3. decrease both input and output resistances

  4. decrease the input resistance and increase the output resistance
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The given solution is right.                    Here  Ri  = input resistance without feedback                              Rif  = input resistance with feedback                              R of  = output resistance with feedback