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. (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,- (…
Correct answer: (L) increases- 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.
Correct answer: RMS value of current- 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…
Correct answer: Different- 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…
Correct answer: The capacitive reactance is halved- 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.
Correct answer: That steady current that produces the same rate of heating in a resistor as the actual current- 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}}…
Correct answer: (220 times sqrt{2})- 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…
Correct answer: radiation of suitable wavelength falls on it- 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.
Correct answer: consists of- 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…
Correct answer: increases- 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…
Correct answer: 5.67 x 10^-8 Wm^-2K^-4- 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…
Correct answer: ferromagnetic- 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.
Correct answer: time base generator- 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…
Correct answer: 8000- 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.
Correct answer: type of semiconductor- A. γ rays
- B. UV
- C. Microwaves
- D. X rays
Explanation: Electromagnetic radiation consists of various types of waves with different wavelengths.
Correct answer: Microwaves- A. 1.0 x 10^6 Hz
- B. 1.0 x 10^9 Hz
- C. 1.0 x 10^12 Hz
- D. 1.0 x 10^15Hz
Explanation: The frequency of electromagnetic waves, including ultraviolet radiation, is often measured in hertz (Hz), where 1 Hz is equivalent to one…
Correct answer: 1.0 x 10^15Hz- A. Infrared
- B. X-rays
- C. UV
- D. Gamma rays
Explanation: The electromagnetic spectrum consists of various types of radiation, each with a different wavelength.
Correct answer: Infrared- A. 10-10
- B. 10-8
- C. 10-4
- D. 10-12
Explanation: The value for the wavelength of X-rays is 10-10 corresponding to frequencies in the range of 30 petahertz (PHz) to 30 exahertz (EHz).
Correct answer: 10-10- A. Cell
- B. Skin
- C. Hair
- D. All of these
Explanation: The dosage of radiations is measured in sieverts or microsieverts given by the formula:De = D x RBE where D = energy from radiation / mass…
Correct answer: All of these- A. Gamma rays
- B. Light
- C. Radio waves
- D. All of these
Explanation: All of the above waves belong to electromagnetic waves. In space, electromagnetic waves travel at the same speed which is the speed of…
Correct answer: All of these