Electromagnetic Wave

Assertion and Reason Questions Chapter-8 Electromagnetic Wave

Assertion (A) and other labelled Reason (R). Select the correct answer to these questions from the options as given below.

A. Both A and R are true, and R is the correct explanation of A.

B. Both A and R are true, but R is not the correct explanation of A.

C. A is true, but R is false.

D. A is false, but R is true.

1. Assertion (A): Electromagnetic waves can travel through a vacuum.

Reason (R): Electromagnetic waves do not require a medium for propagation.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Electromagnetic waves are self-propagating and do not need a medium, which allows them to travel through a vacuum.

2. Assertion (A): The speed of electromagnetic waves in a vacuum is equal to the speed of light.

Reason (R): The speed of light is constant in all inertial frames of reference.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Electromagnetic waves travel at the speed of light in a vacuum, and this speed is invariant across different frames.

3. Assertion (A): Electromagnetic waves consist of oscillating electric and magnetic fields.

Reason (R): The electric field and magnetic field are perpendicular to each other in an electromagnetic wave.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The oscillating electric and magnetic fields in electromagnetic waves are indeed perpendicular to each other, as well as to the direction of wave propagation.

4. Assertion (A): Radio waves have a longer wavelength than visible light.

Reason (R): The energy of a photon is inversely proportional to its wavelength.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Radio waves have longer wavelengths compared to visible light, and the energy of photons decreases with increasing wavelength.

5. Assertion (A): Electromagnetic waves are transverse waves.

Reason (R): In transverse waves, the particle displacement is perpendicular to the direction of wave propagation.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Electromagnetic waves are classified as transverse because the oscillations of the electric and magnetic fields are perpendicular to the direction of wave propagation.

6. Assertion (A): The frequency of electromagnetic waves is directly proportional to their energy.

Reason (R): Higher frequency waves have longer wavelengths.

• (b) A is true, but R is false.
• Answer: (b)
  Explanation: While the frequency is directly proportional to energy, higher frequency waves actually have shorter wavelengths.

7. Assertion (A): Microwaves can penetrate through certain materials, making them useful for communication.

Reason (R): Microwaves have lower frequencies compared to infrared waves.

• (b) A is true, but R is false.
• Answer: (b)
  Explanation: Microwaves have higher frequencies than infrared waves, which allows them to penetrate materials better.

8. Assertion (A): Ultraviolet rays can cause skin damage.

Reason (R): UV rays have higher energy than visible light.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Ultraviolet rays carry enough energy to damage skin cells, leading to issues like sunburn and increased cancer risk.

9. Assertion (A): The electromagnetic spectrum is a continuous range of wavelengths and frequencies.

Reason (R): Each type of electromagnetic wave has unique properties and uses.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The electromagnetic spectrum encompasses all types of electromagnetic radiation, each with distinct properties that make them useful for various applications.

10. Assertion (A): Gamma rays are the most energetic form of electromagnetic radiation.

Reason (R): Gamma rays have the longest wavelengths in the electromagnetic spectrum.

• (b) A is true, but R is false.
• Answer: (b)
  Explanation: Gamma rays are indeed the most energetic, but they have the shortest wavelengths, not the longest.

11. Assertion (A): Infrared radiation is used in remote controls.

Reason (R): Infrared waves are invisible to the human eye.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Infrared radiation is commonly used in remote controls because it is invisible, allowing for discreet operation.

12. Assertion (A): The electric and magnetic fields in electromagnetic waves oscillate in phase.

Reason (R): This phase relationship ensures the wave propagates effectively.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The electric and magnetic fields oscillate together in phase, ensuring the wave propagates effectively through space.

13. Assertion (A): Electromagnetic waves can exert pressure on surfaces.

Reason (R): This pressure is due to the momentum carried by the waves.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Electromagnetic waves carry momentum, which can exert pressure when they interact with surfaces, such as in solar sails.

14. Assertion (A): X-rays are used in medical imaging.

Reason (R): X-rays can penetrate soft tissues but are absorbed by denser materials like bones.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: X-rays are effective in medical imaging because they can pass through soft tissues while being absorbed by denser tissues, creating contrasting images.

15. Assertion (A): Electromagnetic waves can be polarized.

Reason (R): Polarization is a characteristic of transverse waves.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Since electromagnetic waves are transverse, they can be polarized, which is a property of such waves.

16. Assertion (A): The energy of an electromagnetic wave is carried by its electric field.

Reason (R): The magnetic field does not contribute to the energy of the wave.

• (b) A is true, but R is false.
• Answer: (b)
  Explanation: Both the electric and magnetic fields carry energy; hence, both contribute to the total energy of the electromagnetic wave.

17. Assertion (A): Electromagnetic waves are produced by charged particles in acceleration.

Reason (R): Accelerating charges emit electromagnetic radiation in all directions.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: When charged particles accelerate, they create disturbances in the electric and magnetic fields, producing electromagnetic waves.

18. Assertion (A): Light behaves as both a particle and a wave.

Reason (R): This dual nature is fundamental to quantum mechanics.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The dual wave-particle nature of light is a cornerstone of quantum mechanics, explaining various phenomena like the photoelectric effect.

19. Assertion (A): The intensity of electromagnetic waves decreases with distance from the source.

Reason (R): The energy spreads out over an increasing area as it propagates.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: As electromagnetic waves move away from the source, their intensity diminishes because the energy is distributed over a larger area.

20. Assertion (A): Electromagnetic waves can be reflected and refracted.

Reason (R): Reflection and refraction are properties of all types of waves.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Just like sound and water waves, electromagnetic waves can reflect and refract, demonstrating wave behavior.

21. Assertion (A): The frequency of a wave is inversely proportional to its wavelength.

Reason (R): This relationship is described by the equation c= \(\ \lambda f \).

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The speed of light equation c= \(\ \lambda f \) illustrates that as frequency increases, wavelength decreases, confirming their inverse relationship.

22. Assertion (A): The Doppler effect applies to electromagnetic waves.

Reason (R): The frequency of the wave changes when the source or observer moves.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The Doppler effect occurs with all types of waves, including electromagnetic waves, causing shifts in frequency based on relative motion.

23. Assertion (A): Electromagnetic waves can carry information.

Reason (R): Information can be modulated onto electromagnetic waves for transmission.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Modulating signals onto electromagnetic waves allows for information transfer in technologies like radio, television, and wireless communication.

24. Assertion (A): The ultraviolet region of the electromagnetic spectrum is between visible light and X-rays.

Reason (R): Ultraviolet rays have longer wavelengths than X-rays.

• (b) A is true, but R is false.
• Answer: (b)
  Explanation: While the ultraviolet region is between visible light and X-rays, it has shorter wavelengths than X-rays.

25. Assertion (A): All electromagnetic waves travel at the same speed in vacuum.

Reason (R): The speed of light in vacuum is a universal constant.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: All electromagnetic waves, regardless of their frequency or wavelength, travel at the speed of light in a vacuum, which is constant.

26. Assertion (A): The wavelength of electromagnetic waves determines their color in the visible spectrum.

Reason (R): Different colors correspond to different energies of photons.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: In the visible spectrum, each color corresponds to a specific wavelength, which in turn relates to the energy of the photons.

27. Assertion (A): Polarizers can be used to reduce glare from surfaces.

Reason (R): Polarizers allow only light waves vibrating in a particular direction to pass through.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Polarizers filter out certain orientations of light waves, reducing glare from reflective surfaces.

28. Assertion (A): The energy carried by electromagnetic waves is quantized.

Reason (R): Energy quantization is described by the concept of photons.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Electromagnetic waves can be understood in terms of photons, which have quantized energy levels based on frequency.

29. Assertion (A): Electromagnetic waves can be absorbed by matter.

Reason (R): Absorption occurs when the energy of the wave matches the energy levels of electrons in the material.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: When electromagnetic wave energy matches the energy difference of electrons in matter, it can be absorbed, causing transitions.

30. Assertion (A): Diffraction of electromagnetic waves occurs when they encounter obstacles.

Reason (R): Diffraction is a wave phenomenon resulting from the wave nature of electromagnetic radiation.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The wave nature of electromagnetic radiation allows for diffraction when they interact with obstacles or apertures.

31. Assertion (A): Electromagnetic waves can be used in satellite communication.

Reason (R): Satellites transmit and receive signals in the microwave region of the electromagnetic spectrum.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Microwaves are effectively used for satellite communication due to their ability to penetrate the atmosphere and carry information.

32. Assertion (A): Electromagnetic waves can interact with charged particles.

Reason (R): The oscillating electric field in the wave exerts a force on charged particles.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The electric field component of electromagnetic waves can influence charged particles, causing various interactions.

33. Assertion (A): The electromagnetic spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

Reason (R): Each type of electromagnetic radiation has a unique wavelength and frequency range.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The electromagnetic spectrum comprises various types of radiation, each characterized by its specific wavelength and frequency.

34. Assertion (A): The wavelength of a radio wave can be larger than that of visible light.

Reason (R): Longer wavelengths correspond to lower frequencies.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Radio waves have significantly longer wavelengths than visible light, which is due to their lower frequencies.

35. Assertion (A): The photoelectric effect supports the particle nature of light.

Reason (R): The effect demonstrates that light can knock out electrons from metal surfaces.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The photoelectric effect shows that light behaves as particles (photons) since only light above a certain frequency can release electrons.

36. Assertion (A): Infrared radiation is used in thermal imaging.

Reason (R): Infrared waves are emitted by all objects based on their temperature.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Infrared radiation is emitted by objects depending on their temperature, making it useful for thermal imaging applications.

37. Assertion (A): The frequency of electromagnetic radiation determines its energy.

Reason (R): Energy is directly proportional to frequency according to Planck’s relation.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Planck's equation E=hf shows that energy is directly proportional to frequency, confirming the relationship.

38. Assertion (A): Ultraviolet radiation is harmful to living organisms.

Reason (R): Ultraviolet rays can cause DNA damage in cells.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Ultraviolet radiation can cause mutations in DNA, leading to harmful effects like skin cancer.

39. Assertion (A): X-rays can be used for both imaging and cancer treatment.

Reason (R): X-rays have high energy that can destroy cancer cells.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The high energy of X-rays allows them to penetrate tissues for imaging and target cancer cells for treatment.

40. Assertion (A): The energy of electromagnetic waves increases with increasing frequency.

Reason (R): Higher frequency waves have shorter wavelengths.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: As frequency increases, energy increases while wavelength decreases, confirming their interdependence.

41. Assertion (A): The visible spectrum is a small part of the electromagnetic spectrum.

Reason (R): The visible spectrum ranges from 400 nm to 700 nm.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The visible spectrum is indeed a narrow range compared to the entire electromagnetic spectrum, which encompasses a much broader range of wavelengths.

42. Assertion (A): The electric field and magnetic field of an electromagnetic wave are perpendicular to each other.

Reason (R): Electromagnetic waves propagate in a direction perpendicular to both fields.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: In electromagnetic waves, the electric and magnetic fields are oriented at right angles to each other and the direction of wave propagation.

43. Assertion (A): Light behaves as both a wave and a particle.

Reason (R): Light exhibits phenomena such as interference and photoelectric effect.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The dual nature of light is supported by its wave-like behavior (interference) and particle-like behavior (photoelectric effect).

44. Assertion (A): The speed of electromagnetic waves is independent of their frequency and wavelength.

Reason (R): Electromagnetic waves in a vacuum travel at the speed of light, regardless of their type.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The speed of light in a vacuum is constant for all electromagnetic waves, which does not depend on frequency or wavelength.

45. Assertion (A): Electromagnetic waves do not require a medium for propagation.

Reason (R): Unlike mechanical waves, electromagnetic waves can travel through vacuum.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Electromagnetic waves can propagate through a vacuum, making them distinct from mechanical waves, which require a medium.

46. Assertion (A): Microwaves can be used for cooking food.

Reason (R): Microwaves cause water molecules in food to vibrate, generating heat.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The vibration of water molecules by microwaves generates heat, effectively cooking food.

47. Assertion (A): Gamma rays have the highest frequency in the electromagnetic spectrum.

Reason (R): Higher frequency waves have higher energy than lower frequency waves.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Gamma rays are the most energetic electromagnetic waves due to their high frequency, confirming their position in the spectrum.

48. Assertion (A): The phenomenon of total internal reflection is used in fiber optics.

Reason (R): Fiber optics utilize light transmission by bouncing light internally at angles greater than the critical angle.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Fiber optics rely on total internal reflection to guide light along the fiber, making it an essential technology for telecommunications.

49. Assertion (A): Electromagnetic waves can be produced by oscillating charges.

Reason (R): Accelerating charges emit electromagnetic radiation due to changing electric and magnetic fields.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The emission of electromagnetic waves results from the acceleration of charges, leading to variations in the electric and magnetic fields.

50. Assertion (A): Electromagnetic waves can propagate through space with no loss of energy.

Reason (R): In vacuum, electromagnetic waves face no resistance, unlike mechanical waves.

• (b) A is true, but R is false.
• Answer: (b)
  Explanation: While electromagnetic waves propagate through space without energy loss in an ideal vacuum, real-world conditions (like absorption by materials) can cause energy loss.