Chapter 8: Electromagnetic Waves Assertion-Reason Questions | physics Class 12 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): Maxwell introduced the concept of displacement current to remove the inconsistency in Ampere's circuital law. Reason (R): A time-varying electric flux between the capacitor plates gives rise to a displacement current equal to ε₀(dΦ_E/dt).

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): Inside a charging capacitor, no conduction current exists. Reason (R): Charges do not physically cross the gap between the capacitor plates.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 3

Logic Check

Assertion (A): Electromagnetic waves are transverse in nature. Reason (R): The electric and magnetic fields in an EM wave oscillate parallel to the direction of propagation.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 4

Logic Check

Assertion (A): A stationary electric charge cannot produce electromagnetic waves. Reason (R): Electromagnetic waves are produced only by accelerated charges.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 5

Logic Check

Assertion (A): All electromagnetic waves travel at the same speed c in vacuum regardless of their frequency. Reason (R): The speed c = 1/√(µ₀ε₀) depends only on the fundamental constants of free space, which are frequency-independent.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 6

Logic Check

Assertion (A): The speed of electromagnetic waves in a material medium is less than their speed in vacuum. Reason (R): In a material medium with permittivity ε and permeability µ, the wave speed v = 1/√(µε), and since ε > ε₀ and µ ≥ µ₀, v < c.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 7

Logic Check

Assertion (A): Light is an electromagnetic wave. Reason (R): Maxwell's equations predict waves with speed equal to c = 1/√(µ₀ε₀), which matches the experimentally measured speed of light.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): The magnetic field amplitude B₀ in an EM wave in vacuum is much smaller than the electric field amplitude E₀ (in SI units). Reason (R): B₀ = E₀/c, and since c = 3 × 10⁸ m/s is very large, B₀ ≪ E₀ numerically.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 9

Logic Check

Assertion (A): The laws of electricity and magnetism become more symmetrical after Maxwell's modification. Reason (R): Faraday's law shows changing B produces E, while the Ampere-Maxwell law shows changing E produces B — each field generates the other.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 10

Logic Check

Assertion (A): Gauss's law for magnetism (∮B·dA = 0) implies that magnetic monopoles do not exist. Reason (R): A non-zero right-hand side in ∮B·dA = 0 would imply isolated sources of magnetic field, analogous to electric charges for electric fields.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 11

Logic Check

Assertion (A): Radio waves and gamma rays are fundamentally different types of waves requiring different media for propagation. Reason (R): All electromagnetic waves, including radio waves and gamma rays, travel through vacuum at the same speed c and differ only in frequency.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 12

Logic Check

Assertion (A): Infrared waves are called heat waves. Reason (R): Water molecules and many other molecules readily absorb infrared radiation, increasing their thermal motion and heating the substance.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 13

Logic Check

Assertion (A): The frequency of an EM wave changes when it travels from vacuum into a glass medium. Reason (R): The speed of EM waves decreases in a medium, and since c = νλ, if speed decreases, wavelength decreases but frequency remains unchanged.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): UV radiation is used in LASIK eye surgery. Reason (R): UV radiation can be focused into a very narrow beam due to its shorter wavelength, enabling high precision corneal tissue ablation.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 15

Logic Check

Assertion (A): The displacement current between the plates of a charging capacitor produces the same magnetic field as the conduction current in the connecting wire. Reason (R): The displacement current iₐ = ε₀(dΦ_E/dt) equals the conduction current i, so both produce the same B field for the same loop radius.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 16

Logic Check

Assertion (A): Microwaves of wavelength 0.1 m to 1 mm are suitable for radar systems used in aircraft navigation. Reason (R): Short wavelengths allow microwaves to be directed into narrow beams and reflected effectively by metallic objects.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 17

Logic Check

Assertion (A): Electromagnetic waves can propagate through vacuum without any material medium. Reason (R): EM waves are self-sustaining oscillations of electric and magnetic fields — no material medium is needed as the fields themselves carry the wave.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 18

Logic Check

Assertion (A): X-rays can be used to detect bone fractures but cannot distinguish between different soft tissues. Reason (R): X-rays are absorbed more strongly by high atomic number materials like calcium in bones, creating contrast against less-absorbing soft tissue.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 19

Logic Check

Assertion (A): The speed of light in vacuum is used to define the SI standard of length (metre). Reason (R): The speed of EM waves is independent of wavelength in vacuum and is so precisely known that it serves as a better reference than mechanical length standards.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 20

Logic Check

Assertion (A): The centre of sensitivity of the human eye coincides with the centre of the wavelength distribution of the sun. Reason (R): Humans have evolved with vision most sensitive to the wavelengths most strongly emitted by the sun.

Reasoning Options

ByteNotes

Chapter sections

Chapter 8: Electromagnetic Waves | Assertion-Reason

Assertion (A): Maxwell introduced the concept of displacement current to remove the inconsistency in Ampere's circuital law. Reason (R): A time-varying electric flux between the capacitor plates gives rise to a displacement current equal to ε₀(dΦ_E/dt).

Assertion (A): Inside a charging capacitor, no conduction current exists. Reason (R): Charges do not physically cross the gap between the capacitor plates.

Assertion (A): Electromagnetic waves are transverse in nature. Reason (R): The electric and magnetic fields in an EM wave oscillate parallel to the direction of propagation.

Assertion (A): A stationary electric charge cannot produce electromagnetic waves. Reason (R): Electromagnetic waves are produced only by accelerated charges.

Assertion (A): All electromagnetic waves travel at the same speed c in vacuum regardless of their frequency. Reason (R): The speed c = 1/√(µ₀ε₀) depends only on the fundamental constants of free space, which are frequency-independent.

Assertion (A): The speed of electromagnetic waves in a material medium is less than their speed in vacuum. Reason (R): In a material medium with permittivity ε and permeability µ, the wave speed v = 1/√(µε), and since ε > ε₀ and µ ≥ µ₀, v < c.

Assertion (A): Light is an electromagnetic wave. Reason (R): Maxwell's equations predict waves with speed equal to c = 1/√(µ₀ε₀), which matches the experimentally measured speed of light.

Assertion (A): The magnetic field amplitude B₀ in an EM wave in vacuum is much smaller than the electric field amplitude E₀ (in SI units). Reason (R): B₀ = E₀/c, and since c = 3 × 10⁸ m/s is very large, B₀ ≪ E₀ numerically.

Assertion (A): The laws of electricity and magnetism become more symmetrical after Maxwell's modification. Reason (R): Faraday's law shows changing B produces E, while the Ampere-Maxwell law shows changing E produces B — each field generates the other.

Assertion (A): Gauss's law for magnetism (∮B·dA = 0) implies that magnetic monopoles do not exist. Reason (R): A non-zero right-hand side in ∮B·dA = 0 would imply isolated sources of magnetic field, analogous to electric charges for electric fields.

Assertion (A): Radio waves and gamma rays are fundamentally different types of waves requiring different media for propagation. Reason (R): All electromagnetic waves, including radio waves and gamma rays, travel through vacuum at the same speed c and differ only in frequency.

Assertion (A): Infrared waves are called heat waves. Reason (R): Water molecules and many other molecules readily absorb infrared radiation, increasing their thermal motion and heating the substance.

Assertion (A): The frequency of an EM wave changes when it travels from vacuum into a glass medium. Reason (R): The speed of EM waves decreases in a medium, and since c = νλ, if speed decreases, wavelength decreases but frequency remains unchanged.

Assertion (A): UV radiation is used in LASIK eye surgery. Reason (R): UV radiation can be focused into a very narrow beam due to its shorter wavelength, enabling high precision corneal tissue ablation.

Assertion (A): Microwaves of wavelength 0.1 m to 1 mm are suitable for radar systems used in aircraft navigation. Reason (R): Short wavelengths allow microwaves to be directed into narrow beams and reflected effectively by metallic objects.

Assertion (A): Electromagnetic waves can propagate through vacuum without any material medium. Reason (R): EM waves are self-sustaining oscillations of electric and magnetic fields — no material medium is needed as the fields themselves carry the wave.

Assertion (A): X-rays can be used to detect bone fractures but cannot distinguish between different soft tissues. Reason (R): X-rays are absorbed more strongly by high atomic number materials like calcium in bones, creating contrast against less-absorbing soft tissue.

Assertion (A): The speed of light in vacuum is used to define the SI standard of length (metre). Reason (R): The speed of EM waves is independent of wavelength in vacuum and is so precisely known that it serves as a better reference than mechanical length standards.

Assertion (A): The centre of sensitivity of the human eye coincides with the centre of the wavelength distribution of the sun. Reason (R): Humans have evolved with vision most sensitive to the wavelengths most strongly emitted by the sun.

Unlock all Assertion-Reason Questions

Practice in Quiz Mode