NEETPhysicsMagnetic Properties of Matter
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): When an electromagnetic wave travels from vacuum into a non-magnetic dielectric medium, its propagation speed ( E₀/B₀ ) decreases but the ratio of electric field amplitude to magnetic intensity amplitude ( E₀/H₀ ) increases. Reason (R): For a non-magnetic dielectric medium, relative permeability is
Options
- ABoth (A) and (R) are correct and (R) is the correct explanation of (A)
- BBoth (A) and (R) are correct but (R) is not the correct explanation of (A)
- C(A) is correct but (R) is not correct
- D(A) is not correct but (R) is correct
Correct answer
D. (A) is not correct but (R) is correct
Step-by-step solution
The propagation speed of an electromagnetic wave is given by v = E₀ B₀ = 1 . The ratio of electric field amplitude to magnetic intensity amplitude (wave impedance) is given by E₀ H₀ = . For a non-magnetic dielectric medium, the relative permeability _r = 1 (so = ₀ ) and the relative permittivity _r > 1 (so > ₀ ). Substituting these values, the speed becomes v = 1 ₀ ₀ _r , which is less than the speed in vacuum ( c = 1 ₀ ₀ ). Thus, the propagation speed decreases. Similarly, the ratio E₀ H₀ becomes ₀ ₀ _r , which is