Free Alternating Current MCQs with Answers

• A. Inertia frames of reference
• B. Navstar
• C. Proton
• D. None of these

Explanation: Navstar is the satellite navigation system developed by the United States and commonly associated with GPS.

• A. Less than ordinary light
• B. More than ordinary light
• C. Equal to ordinary light
• D. Different for different colours or frequency

Explanation: Laser light is electromagnetic radiation, so in vacuum it travels at the same speed as ordinary light, approximately 3.0 x 10^8 m/s.

• A. Heating the filament
• B. Electron excitation in the gas
• C. Ionization of atoms
• D. All the above

Explanation: Ultraviolet radiation can be produced when electrons in a gas are excited to higher energy levels and then fall to lower levels, emitting…

• A. Cathode rays
• B. Positive rays
• C. γ-rays
• D. Beta rays

Explanation: X-rays and gamma rays are both high-frequency electromagnetic waves and differ mainly in their origin, not in their fundamental nature.

• A. Light waves
• B. Heat waves
• C. Microwaves
• D. γ-rays

Explanation: X-rays and gamma rays are both high-frequency electromagnetic waves and differ mainly by their origin, not by their basic nature.

• A. Refrigeration
• B. Aerosol spray
• C. Plastic foam industry
• D. All of above

Explanation: CFCs have been used as refrigerants, propellants in aerosol sprays and blowing agents in the manufacture of plastic foams.

• A. Stationary
• B. Longitudinal
• C. Transverse
• D. All the above

Explanation: Electromagnetic waves are transverse because their electric and magnetic fields oscillate perpendicular to the direction of propagation.

• A. Perpendicular to electric field
• B. Perpendicular to both electric and magnetic field
• C. Perpendicular to magnetic field
• D. Parallel to electric and magnetic field

Explanation: In an electromagnetic wave, the electric field, magnetic field, and direction of propagation are mutually perpendicular.

• A. Electric and magnetic fields moving parallel to each other
• B. Magnetic field moving with velocity of light in space
• C. Electric field moving with velocity of light
• D. Electric and magnetic fields moving perpendicular to each other

Explanation: An electromagnetic wave contains oscillating electric and magnetic fields that are perpendicular to each other and to the direction of…

• A. λ-rays
• B. Positive rays
• C. Cathode rays
• D. More than sound waves

Explanation: Gamma rays, apparently intended by λ-rays, are electromagnetic waves and travel in free space at the speed of light, approximately 3.0 x…

• A. A digital waveform
• B. An analogue waveform
• C. Discrete waveform
• D. None at all

Explanation: An alternating voltage changes continuously with time and can take a range of values, so it is an analogue waveform.

• A. I = 2I∫Sin(πt/2)
• B. I = 2I∫Sin(2πt)
• C. I = 2ISinπt
• D. I = I∫sin(2πt)

Explanation: The original current has amplitude I₀ and angular frequency π rad/s, so doubling both gives I = 2I₀ sin(2πt), with amplitude 2I₀ and…

• A. Mean value of I2
• B. Square root of mean value of I2
• C. Square root of I2
• D. Square of 1/2

Explanation: The RMS current is defined as the square root of the mean of the square of the instantaneous current: Irms = √(mean of I²).

• A. 20A
• B. 20.66A
• C. 6.66A
• D. 5.66A

Explanation: For a sinusoidal current, Ipeak = √2 Irms = 1.414 x 4.0 A = 5.66 A. The frequency of 50 Hz and resistance of 10 Ω are not needed to find…

• A. Average current
• B. Sinusoidal current
• C. r.m.s current
• D. Net current

Explanation: Heating in a resistor depends on I²R, so the steady current producing the same average heating as an AC current is its RMS current.

• A. Resistor
• B. Inductor
• C. Capacitor
• D. All the three

Explanation: This is the correct answer. All three elements-resistor, inductor, and capacitor-are basic and fundamental components of A.C circuits.

• A. From a source which is not the same as the unknown voltage.
• B. From a battery.
• C. From the same source as the unknown voltage
• D. Any of the above

Explanation: The correct answer is option (a) - From a source which is not the same as the unknown voltage.

• A. 90o
• B. 0o
• C. 180o
• D. None of these

Explanation: This is the correct answer. In a purely resistive A.C circuit, the current and voltage are in phase with each other, meaning they are…

• A. Leads the voltage by 90o or π/2
• B. Lags behind voltage by 90o or π/2
• C. In phase with voltage
• D. None of the above

Explanation: This is the correct answer. In a circuit with only a capacitor, the current leads the voltage by 90 degrees (π/2 radians) in phase.

• A. In the resistor, I leads V by 90 degrees - In the capacitor, I leads V by 90 degrees
• B. In the resistor, I lags V by 90 degrees - In the capacitor, I leads V by 90 degrees
• C. In the resistor, I and V are in phase - In the capacitor, I leads V by 90 degrees
• D. In the resistor, I and V are in phase - In the capacitor, I lags V by 90 degrees
• E. In the resistor, I lags V by 90 degrees - In the capacitor, I lags V by 90 degrees

Explanation: In a resistor, the current and voltage are in phase because the current flows in the same direction as the voltage.