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
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220 volts
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440 volts
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120 volts
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240 volts
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.
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Transistor
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Resistor
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Transformer
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Generator
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.
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Current is constant
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Voltage is constant
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Current gets divided
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Current is equal to zero
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Voltage is zero
A
Correct answer
Explanation
A battery can be made to approximate a constant current source by adding a series resistance - the larger the resistance, the better the approximation - and the lower the current.
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Copper loss will be less.
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Noise level will be reduced.
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Iron losses will be more.
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Iron losses will be less.
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None of these
D
Correct answer
Explanation
The peaked wave has a lesser rms voltage than the sinusoidal wave.
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copper loss
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copper and eddy current losses
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eddy current and hysteresis losses
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copper loss, eddy current loss and hysteresis loss
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None of these
C
Correct answer
Explanation
Eddy current and hysteresis losses are constant losses.
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Yes
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No
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No, resistance has to be decreased
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Yes, at constant voltage
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None of these
B
Correct answer
Explanation
Core is at excessive saturation. Flux is to be doubled.
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eddy current and hysteresis loss of the transformer decreases
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eddy current and hysteresis increases
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hysteresis loss increases, while eddy current remains the same
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hysteresis loss remains the same, whereas eddy current decreases
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None of these
A
Correct answer
Explanation
Yes, it is the correct choice.
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Induced voltage is proportional to speed and armature current.
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Torque is proportional to square of armature current.
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Armature current is inversely proportional to speed for a constant Ea.
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Only 1 and 2
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1, 2 and 3
E
Correct answer
Explanation
Options 1, 2 and 3 are correct.
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OC test gives magnetic current and core loss at rated voltage.
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OC test gives sum of hysteresis and eddy current losses.
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OC test is performed with rated transformer voltage.
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All of the above
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None of these
D
Correct answer
Explanation
Yes, it's the correct choice.
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Resistance start
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Inductance start
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Capacitance start
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Split phase motor
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Electrolyte capacitor
C
Correct answer
Explanation
Yes, capacitance start single phase motor is very economical.
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arc lightening
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arc cooling
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arc splitting
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Only 1 and 2
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1, 2 and 3
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motor
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oscillator
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rectifier
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transformer
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.
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Live wire
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Neutral wire
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Earth wire
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Both 1 and 2
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All of the above
D
Correct answer
Explanation
This is the correct answer.
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Oscillator
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Amplifier
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Rectifier
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None of these
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.
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Live wire only
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Live wire and the earth wire
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Live wire and the neutral wire
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Earth wire and the neutral wire
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.