Free Alternating Current MCQs with Answers

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

Explanation: [ I_{{rms}} = frac{I_{{peak}}}{sqrt{2}} ]We can rearrange this formula to find the peak current:[ I_{{peak}} = I_{{rms}} times sqrt{2}…

• A. 2 A
• B. ( sqrt{2} ) A
• C. 1 A
• D. ( 2sqrt{2} ) A

Explanation: For the alternating current (r.m.s) and the direct current to produce heat at the same rate in identical resistors, their powers must be…

• A. Lagging each other
• B. At a 90° phase difference
• C. Zero phase difference
• D. No phase difference

Explanation: In a pure resistor circuit, the voltage and current are in phase with each other. This means that they have zero phase difference.

• A. Unity when the circuit contains only an inductance
• B. Unity when the circuit contains only a resistance
• C. Unity when the circuit contains resistance and capacitor
• D. Unity when the circuit contains only a capacitance

Explanation: The power factor (PF) of an AC circuit is the cosine of the angle between the voltage and current waveforms.

• A. Lags behind voltage by π/2
• B. Is in phase with voltage
• C. Is opposite in phase of voltage by π
• D. Leads the voltage by π/2

Explanation: In a capacitive circuit, the current leads the voltage by a phase angle of ( frac{pi}{2} ) radians, or 90 degrees.

• A. Remains the same
• B. Brightness increases
• C. Brightness decreases
• D. No light

Explanation: When a dielectric material, like a glass plate, is introduced between the plates of a capacitor, it increases the capacitance.

• A. (C) decreases
• B. (R) increases
• C. (L) decreases
• D. (L) increases

Explanation: The impedance ((Z)) in an RLC series circuit is given by the formula:[ Z = sqrt{R^2 + (X_L - X_C)^2} ]where:- ( R ) is the resistance,- (…

• A. Exact value of current
• B. RMS value of current
• C. Net value of current
• D. Peak value of current

Explanation: An ammeter measures the current in a circuit. In an AC (alternating current) circuit, the current varies sinusoidally over time.

• A. Same
• B. Different
• C. ( V_{{L}} ) will be more than ( V_{{C}} )
• D. ( V_{{L}} ) will be less than ( V_{{C}} )

Explanation: When a pure inductor and a pure capacitor are connected in parallel to a sinusoidal potential difference ( V ), the potential difference…

• A. The capacitive reactance is doubled
• B. The capacitive reactance is halved
• C. The impedance is doubled
• D. The current amplitude is halved

Explanation: The capacitive reactance ((X_C)) in a series RLC circuit is given by the formula:[ X_C = frac{1}{2pi f C} ]where ( f ) is the frequency…

• A. Its peak value
• B. Its average value
• C. That steady current that produces the same rate of heating in a resistor as the actual current
• D. That steady current that charges a battery at the same rate as the actual current

Explanation: The RMS (Root Mean Square) value of an AC current is a way to represent its effective or equivalent DC value.

• A. 220V
• B. (frac{220}{sqrt{2}})
• C. 110V
• D. (220 times sqrt{2})

Explanation: In an AC circuit, the peak voltage ((V_{{peak}})) is related to the RMS voltage ((V_{{rms}})) by the formula:[ V_{{peak}} = V_{{rms}}…

• A. it is heated to a high temperature
• B. electrons of suitable velocity strike it
• C. radiation of suitable wavelength falls on it
• D. it is placed in a strong electric field

Explanation: The photoelectric effect occurs when radiation of suitable wavelength (typically in the ultraviolet or higher energy range) falls on the…

• A. is a transverse wave
• B. can be polarized
• C. is a longitudinal wave
• D. consists of

Explanation: The photoelectric effect can be explained only by assuming that electromagnetic radiation consists of quanta or photons.

• A. decreases
• B. remain same
• C. increases
• D. none of these

Explanation: According to Wien's displacement law, as the temperature increases, the proportion of shorter wavelengths in the emitted radiation…

• A. 5.67 x 10^-8 Wm^-2K^-4
• B. 5.67 x 10^-6 Wm^-2K^-4
• C. 2.9 x 10^-3 mK
• D. 6.63 x 10^-24 Js

Explanation: Stefan's constant (σ) is a physical constant that relates the total energy radiated per unit surface area of a black body to its…

• A. non-magnetic
• B. paramagnetic
• C. diamagnetic
• D. ferromagnetic

Explanation: The concept of domains is related to ferromagnetic materials. In ferromagnetic materials, such as iron, nickel, and cobalt, small regions…

• A. time base generator
• B. electric base generator
• C. X supplier
• D. power supply

Explanation: This specific circuit in a CRO generates a sawtooth waveform that is applied to the X plates.

• A. 2000
• B. 4000
• C. 6000
• D. 8000

Explanation: To increase the range of a voltmeter to measure a higher voltage, you need to connect a series resistance (also called a multiplier) to…

• A. forward voltage
• B. reverse current
• C. forward current
• D. type of semiconductor

Explanation: The color of light emitted by a light-emitting diode (LED) depends on the d.