Free Electromagnetic Waves MCQs with Answers
92 Electromagnetic Waves MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Electromagnetic waves consist of mutually perpendicular, oscillating electric and magnetic fields that also remain perpendicular to the direction of propagation. They travel through vacuum at the speed of light and include radio waves, microwaves, infrared, visible, ultraviolet, X-rays and gamma rays. Unlike mechanical waves, they do not require a material medium.
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- A. Space waves
- B. Cable waves
- C. Antenna waves
- D. None of these
Explanation: Line-of-sight communication uses space waves, which travel directly from the transmitting antenna to the receiving antenna through the…
Correct answer: Space waves- A. . dc circuit
- B. ac circuit
- C. both ac and dc
- D. full wave rectifier circuit
Explanation: Answer: b. ac circuitExplanation: A choke is an inductor that is primarily used to provide impedance to alternating current (ac) in a…
Correct answer: ac circuit- A. Zero
- B. 1/2
- C. 1
- D. Not definite
Explanation: Explanation: At resonance in an L-C-R series circuit, the impedance becomes purely resistive, and the power factor is maximum.
Correct answer: 1- A. 1 ohm
- B. 5 ohm
- C. 7 ohm
- D. ( frac{7}{sqrt{2}} ) ohm
Explanation: Answer: c. 7 ohmExplanation: In an A.C. series circuit, the impedance ((Z)) is given by the formula (sqrt{(R^2 + X_L^2)}), where (R) is…
Correct answer: 7 ohm25. The phase angle between the voltage and the current in an AC circuit consisting of a resistance is:
- A. zero
- B. 45 degrees
- C. 90 degrees
- D. 180 degrees
Explanation: Answer: a. zeroExplanation: In an AC circuit containing only resistance, the voltage and current are in phase with each other.
Correct answer: zero- A. ( C_i/2 )
- B. ( C_i/4 )
- C. ( 2C_i )
- D. ( 4C_i )
Explanation: Answer: (b) ( C_i/4 )Explanation: The resonant frequency (( f )) of an LC circuit is given by the formula ( f = frac{1}{2pisqrt{LC}} )…
Correct answer: ( C_i/4 )- A. positive
- B. negative
- C. both
- D. zero
Explanation: In an alternating current (AC) circuit, the current and voltage vary sinusoidally over time.
Correct answer: both- A. magnetic field
- B. electric field
- C. electromagnetic force
- D. artificial gravitational field
Explanation: According to Faraday's law of electromagnetic induction, a changing magnetic flux induces an electromotive force (EMF) or voltage in a…
Correct answer: electric field- 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: The correct option is (b) because electromagnetic waves consist of both electric and magnetic fields oscillating perpendicular to each…
Correct answer: Perpendicular to both electric and magnetic field- A. Electric and magnetic fields moving parallel to each other
- B. Magnetic field moving with the velocity of light in space
- C. Electric field moving with the velocity of light
- D. Electric and magnetic fields moving perpendicular to each other
Explanation: An electromagnetic wave is a transverse wave, meaning that the electric and magnetic fields oscillate perpendicular to the direction of…
Correct answer: Electric and magnetic fields moving perpendicular to each other- A. Energy
- B. Mass
- C. Heat
- D. None
Explanation: Electromagnetic waves, including light, are a form of energy transfer. They do not carry mass; instead, they transport energy through…
Correct answer: Energy- A. Sound waves
- B. Electromagnetic waves
- C. Radio waves
- D. Modulated waves
Explanation: When waves are emitted from an antenna, they are typically radio waves.
Correct answer: Radio waves33. If the capacitance of an L-C circuit is made four times, then the frequency of the circuit becomes:
- A. Twice
- B. One-half
- C. Four times
- D. None
Explanation: The resonant frequency ((f_0)) of a series L-C circuit is inversely proportional to the square root of the product of inductance (L) and…
Correct answer: One-half- A. Mean value of 12
- B. Square root of mean value of 12
- C. Square root of 12
- D. Square of 1/2
Explanation: The Root Mean Square (R.M.S) value of an alternating current is calculated using the following formula:[ I_{{rms}} = sqrt{frac{1}{T}…
Correct answer: Square root of mean value of 12- 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}…
Correct answer: 5.66 A- 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…
Correct answer: 2 A- 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.
Correct answer: 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.
Correct answer: Unity when the circuit contains only a resistance- 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.
Correct answer: Lags behind voltage by π/2- 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.
Correct answer: Brightness decreases