Free Electromagnetic Waves MCQs with Answers

• A. vibrating particles of a medium
• B. oscillating electric and magnetic fields at right angles to each other and to the direction of travel
• C. a stream of charged particles
• D. longitudinal compressions and rarefactions

Explanation: A changing electric field generates a magnetic field and vice versa, so the two sustain each other and the wave propagates without needing…

• A. Gamma rays
• B. X rays
• C. Visible light
• D. Radio waves

Explanation: The spectrum runs from radio waves at the long wavelength, low frequency, low energy end through microwaves, infrared, visible light and…

• A. 3 times 10 to the 8 m per second, whatever their frequency
• B. different for each frequency
• C. 340 m per second
• D. dependent on the intensity

Explanation: In a vacuum every electromagnetic wave from radio to gamma travels at the same speed c, so wavelength and frequency vary inversely.

• A. is absorbed strongly by water molecules, which then rotate and heat the food
• B. ionises the food
• C. reflects off water
• D. changes the chemical composition of the food

Explanation: The oscillating field makes polar water molecules flip back and forth, and the friction between them heats the food from within rather…

• A. travel faster
• B. have a longer wavelength
• C. carry more energy, enough to break chemical bonds in DNA
• D. are more numerous in sunlight

Explanation: Photon energy is proportional to frequency, so the shorter wavelength ultraviolet carries enough energy per photon to damage the bonds in…

• A. X-rays
• B. Ultraviolet rays
• C. Gamma rays
• D. Microwaves

Explanation: Gamma rays sit at the extreme short wavelength end of the electromagnetic spectrum, so they carry the highest frequency and photon energy…

• 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. Visible light
• B. X rays
• C. Ultraviolet rays
• D. Gamma rays

Explanation: Reasoning:Energy of electromagnetic waves is directly proportional to their frequency and inversely proportional to their wavelength.

• A. X-rays
• B. Beta rays
• C. Gamma rays
• D. No radiation needs medium to travel

Explanation: Option D is correct because radiation does not need a physical medium to radiate. These radiate in the form of electromagnetic waves.

• A. (velocity)2
• B. 1/velocity
• C. (velocity)1/2
• D. 1/velocity2

Explanation: The product μoεo has the same units as 1/velocity2.

• A. 1.0 kWm-2
• B. 1.4 kWm-2
• C. 1.0 Wm-2
• D. 1.4 Wm-2

Explanation: The correct answer is 1.0 kWm-2 because this is the standard value of solar irradiance reaching the Earth's surface on a clear day at…