A resistor and a capacitor are connected in series to an AC supply. What is the phase relation between the current and the supply voltage?
Correct answer A. Current leads the voltage by an angle between 0° and 90°
Topic / 30 questions
Alternating Current MCQs
Alternating Current MCQs cover phase, phase lag and lead, the behaviour of resistors, capacitors and inductors in AC circuits, reactance, rms values and the electromagnetic spectrum from radio waves to gamma rays. They suit MDCAT, ECAT and FSc revision, and every question on MCQs360 shows its correct answer instantly.
- Electromagnetic Induction 30
- Fluid Dynamics 30
- Electrostatics 30
- Electronics 30
- Electromagnetism 30
- Current Electricity 30
- Work and Energy 30
- Waves 30
- Vectors and Equilibrium 30
- Nuclear Physics 30
- Dawn of Modern Physics 30
- Thermodynamics 30
- Rotational and Circular Motion 30
- Atomic Spectra 30
- Alternating Current 30
- Force and Motion 30
Gamma rays are emitted from which part of an atom?
Correct answer D. The nucleus
Which region of the electromagnetic spectrum lies between infrared and radio waves?
Correct answer D. Microwaves
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Light of wavelength 600 nm travels in a vacuum. Take c = 3.0 × 10⁸ m/s. What is its frequency?
Correct answer B. 5.0 × 10¹⁴ Hz
Which statement best describes an electromagnetic wave?
Correct answer B. Oscillating electric and magnetic fields perpendicular to each other and to the direction of travel
Which region of the electromagnetic spectrum is mainly emitted by warm objects and used in thermal imaging cameras?
Correct answer D. Infrared
Which electromagnetic radiation is produced when fast-moving electrons strike a heavy metal target?
Correct answer C. X-rays
An FM radio station broadcasts at 100 MHz. Take c = 3.0 × 10⁸ m/s. What is the wavelength of its waves?
Correct answer C. 3.0 m
Which statement about electromagnetic waves travelling in a vacuum is correct?
Correct answer B. All travel at the same speed of about 3.0 × 10⁸ m/s
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Which part of the electromagnetic spectrum has the shortest wavelength?
Correct answer A. Gamma rays
Which list places the following electromagnetic waves in order of increasing frequency?
Correct answer B. Radio waves, microwaves, infrared, ultraviolet, X-rays
A 0.50 H inductor of negligible resistance is connected to a 230 V, 50 Hz supply. What rms current flows?
Correct answer B. 1.5 A
The rms value of an alternating current is defined as the value of the steady direct current that ____.
Correct answer B. produces the same heating effect in a given resistor
A capacitor draws 0.50 A from a 50 Hz supply. The frequency is changed to 100 Hz with the same rms voltage. What current does it now draw?
Correct answer C. 1.0 A
A sinusoidal voltage of peak value 100 V is applied across a 50 Ω resistor. What is the average power dissipated?
Correct answer D. 100 W
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An alternating voltage is given by V = 200 sin(100πt), with V in volts and t in seconds. What is its frequency?
Correct answer D. 50 Hz
For a 50 Hz supply, what time delay corresponds to a phase difference of π/2 rad?
Correct answer B. 5.0 ms
Two alternating voltages of the same frequency are such that one reaches its peak a quarter of a period after the other. What is the phase difference between them?
Correct answer D. 90°
In a series RLC circuit, what is the phase difference between the voltage across the inductor and the voltage across the capacitor?
Correct answer A. 180°
At what frequency does a 0.50 H inductor have a reactance of 100 Ω?
Correct answer B. 31.8 Hz
About Alternating Current MCQs
Circuit questions ask about the phase relationship between current and voltage across a pure resistor, inductor and capacitor, and the phase difference between inductor and capacitor voltages in a series RLC circuit. Calculation MCQs use inductive and capacitive reactance to find rms currents from mains supplies. The second part of the unit covers the electromagnetic spectrum: the order of its regions, their sources and uses, such as infrared in thermal imaging and X-rays from fast electrons striking a metal target, and the fact that all electromagnetic waves travel at the same speed in a vacuum.
Key facts to remember
- rms values: V_rms = V₀/√2 and I_rms = I₀/√2 for a sinusoidal supply.
- In a pure resistor, current and voltage are in phase; in a pure inductor, voltage leads current by 90°; in a pure capacitor, current leads voltage by 90°.
- Inductive reactance X_L = 2πfL; capacitive reactance X_C = 1/(2πfC).
- In a series RLC circuit, the voltages across L and C are 180° out of phase.
- Electromagnetic spectrum in order of increasing frequency: radio, microwave, infrared, visible, ultraviolet, X-rays, gamma rays.
- All electromagnetic waves travel at c = 3.0 × 10⁸ m/s in a vacuum.
Exams that include Alternating Current MCQs
Pakistan
- MDCAT
- ECAT (UET)
- NUMS
- AKU
- FSc boards
India
- NEET
- JEE Main
Bangladesh
- HSC
- Medical Admission Test
How to prepare for Alternating Current MCQs
- Use the memory aid 'ELI the ICE man': voltage (E) leads current (I) in an inductor (L); current leads voltage in a capacitor (C).
- Remember that X_L rises with frequency while X_C falls, so inductors block high frequencies and capacitors block low ones.
- Learn where each type of radiation comes from: gamma rays from the nucleus, X-rays from electrons hitting a target.
- For reactance calculations, find X first, then use I_rms = V_rms/X.
Frequently asked questions
Which exams ask Alternating Current MCQs?
Alternating Current is part of the FSc physics syllabus, so its MCQs appear in MDCAT, ECAT (UET), NUMS and AKU entry tests and in FSc board papers. Students in India meet the same ideas in NEET and JEE Main, and Bangladeshi students in HSC and the medical admission test.
What is the phase relationship in a capacitor in an AC circuit?
In a purely capacitive AC circuit, the current leads the voltage by 90°, or a quarter of a cycle. The current is greatest when the voltage is zero and changing fastest. In a pure inductor the opposite is true, with voltage leading current by 90°.
Last reviewed October 2026