Maxwell's Electromagnetic Theory — IISER Physics MCQs with Solutions
Free IISER Physics Maxwell's Electromagnetic Theory MCQs with step-by-step solutions (18 questions). Part of Wave Theory of Light. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Maxwell's Electromagnetic Theory · easy · theory
According to Maxwell's electromagnetic theory, light is:
A. A stream of photons only
B. A longitudinal mechanical wave
C. A transverse electromagnetic wave ✓ Correct
D. A stream of corpuscles
Solution: Maxwell showed that light is a transverse electromagnetic wave consisting of oscillating electric and magnetic fields.
Q2 — Maxwell's Electromagnetic Theory · easy · theory
In an electromagnetic wave, the electric field (E), magnetic field (B) and direction of propagation are:
A. Mutually perpendicular to one another ✓ Correct
B. E and B along the direction of propagation
C. All parallel to one another
D. E parallel to B, both perpendicular to propagation
Solution: E, B and the direction of propagation form a mutually perpendicular right-handed set; E and B oscillate in phase.
Q3 — Maxwell's Electromagnetic Theory · medium · theory
The speed of an electromagnetic wave in free space is given by:
A. $c = \sqrt{\mu_0 \varepsilon_0}$
B. $c = \dfrac{1}{\sqrt{\mu_0 \varepsilon_0}}$ ✓ Correct
C. $c = \dfrac{\mu_0}{\varepsilon_0}$
D. $c = \mu_0 \varepsilon_0$
Solution: Maxwell derived c = 1/√(μ₀ε₀) ≈ 3 × 10⁸ m/s, matching the measured speed of light and identifying light as an EM wave.
Q4 — Maxwell's Electromagnetic Theory · medium · theory
In an electromagnetic wave, the ratio of the amplitude of the electric field (E₀) to that of the magnetic field (B₀) equals:
A. 1/c
B. 1
C. c²
D. The speed of light, c ✓ Correct
Solution: For an EM wave E₀/B₀ = c; the electric and magnetic field magnitudes are related by E = cB at every instant.
Q5 — Maxwell's Electromagnetic Theory · medium · theory
For a non-magnetic transparent medium of relative permittivity εᵣ, the refractive index according to electromagnetic theory is:
A. $n = 1/\sqrt{\varepsilon_r}$
B. $n = \sqrt{\varepsilon_r}$ ✓ Correct
C. $n = \varepsilon_r$
D. $n = \varepsilon_r^2$
Solution: n = √(μᵣεᵣ); for a non-magnetic medium μᵣ ≈ 1, so n = √εᵣ (Maxwell's relation).
Q6 — Maxwell's Electromagnetic Theory · medium · theory
A key advantage of Maxwell's electromagnetic theory over earlier mechanical wave models was that light:
A. Cannot carry energy or momentum
B. Does not require a material medium and can travel through vacuum ✓ Correct
C. Must travel through the luminiferous ether
D. Is made of particles with mass
Solution: EM waves are self-sustaining oscillations of electric and magnetic fields and need no material medium, so light can travel through vacuum.
Q7 — Maxwell's Electromagnetic Theory · easy · theory
Electromagnetic waves were first experimentally produced and detected by:
A. Heinrich Hertz ✓ Correct
B. Thomas Young
C. James Clerk Maxwell
D. Augustin Fresnel
Solution: Heinrich Hertz experimentally generated and detected electromagnetic waves, confirming Maxwell's theoretical prediction.
Q8 — Maxwell's Electromagnetic Theory · medium · theory
The energy in an electromagnetic wave is:
A. Entirely in the magnetic field
B. Shared equally between the electric and magnetic fields ✓ Correct
C. Entirely in the electric field
D. Independent of both fields
Solution: The average energy density is shared equally between the electric and magnetic field components of the wave.
Q9 — Maxwell's Electromagnetic Theory · medium · theory
Which of the following phenomena could NOT be explained by Maxwell's electromagnetic wave theory of light?
A. Polarisation of light
B. Interference of light
C. Diffraction of light
D. The photoelectric effect ✓ Correct
Solution: Maxwell's wave theory explained interference, diffraction and polarisation, but failed to explain the photoelectric effect and black-body radiation, which required the quantum theory.
Q10 — Maxwell's Electromagnetic Theory · medium · numerical
In a medium of refractive index n, the speed of light is v = c/n. Using Maxwell's theory, if a medium has εᵣ = 4 (and μᵣ ≈ 1), the speed of light in it is:
A. $0.75 \times 10^{8}$ m/s
B. $6 \times 10^{8}$ m/s
C. $3 \times 10^{8}$ m/s
D. $1.5 \times 10^{8}$ m/s ✓ Correct
Solution: n = √εᵣ = √4 = 2, so v = c/n = (3 × 10⁸)/2 = 1.5 × 10⁸ m/s.
Q11 — Maxwell's Electromagnetic Theory · medium · numerical
A non-magnetic medium has relative permittivity εᵣ = 4. The speed of light in it (c = 3 × 10⁸ m/s) is:
A. 0.75 × 10⁸ m/s
B. 6 × 10⁸ m/s
C. 3 × 10⁸ m/s
D. 1.5 × 10⁸ m/s ✓ Correct
Solution: n = √εᵣ = 2; v = c/n = 3 × 10⁸/2 = 1.5 × 10⁸ m/s.
Q12 — Maxwell's Electromagnetic Theory · medium · numerical
The relative permittivity of a non-magnetic medium of refractive index 1.5 is:
A. 0.67
B. 1.5
C. 3
D. 2.25 ✓ Correct
Solution: n = √εᵣ ⇒ εᵣ = n² = 1.5² = 2.25.
Q13 — Maxwell's Electromagnetic Theory · medium · numerical
In an EM wave the magnetic field amplitude is 2 × 10⁻⁶ T. The electric field amplitude (c = 3 × 10⁸ m/s) is:
A. 600 V/m ✓ Correct
B. 300 V/m
C. 150 V/m
D. 6.7 × 10⁻¹⁵ V/m
Solution: E₀ = cB₀ = 3 × 10⁸ × 2 × 10⁻⁶ = 600 V/m.
Q14 — Maxwell's Electromagnetic Theory · medium · numerical
An EM wave has electric field amplitude 9 V/m. Its magnetic field amplitude (c = 3 × 10⁸ m/s) is:
A. 3 × 10⁸ T
B. 2.7 × 10⁹ T
C. 3 × 10⁻⁸ T ✓ Correct
D. 9 T
Solution: B₀ = E₀/c = 9/(3 × 10⁸) = 3 × 10⁻⁸ T.
Q15 — Maxwell's Electromagnetic Theory · medium · numerical
A non-magnetic medium has εᵣ = 9. The refractive index and speed of light in it are:
A. n = 3, v = 9 × 10⁸ m/s
B. n = 1.5, v = 2 × 10⁸ m/s
C. n = 9, v = 3.3 × 10⁷ m/s
D. n = 3, v = 1 × 10⁸ m/s ✓ Correct
Solution: n = √9 = 3; v = c/n = 3 × 10⁸/3 = 1 × 10⁸ m/s.
Q16 — Maxwell's Electromagnetic Theory · medium · numerical
A medium has refractive index 2 (non-magnetic). Its relative permittivity is:
A. 8
B. 1.4
C. 2
D. 4 ✓ Correct
Solution: εᵣ = n² = 4.
Q17 — Maxwell's Electromagnetic Theory · hard · numerical
Light of wavelength 600 nm (vacuum) enters a medium of εᵣ = 2.25 (non-magnetic). Its wavelength in the medium is:
A. 400 nm ✓ Correct
B. 267 nm
C. 600 nm
D. 900 nm
Solution: n = √2.25 = 1.5; λ_medium = 600/1.5 = 400 nm.
Q18 — Maxwell's Electromagnetic Theory · medium · numerical
For a non-magnetic medium with εᵣ = 16, the speed of light in it (c = 3 × 10⁸ m/s) is:
A. 0.75 × 10⁸ m/s ✓ Correct
B. 12 × 10⁸ m/s
C. 1.5 × 10⁸ m/s
D. 3 × 10⁸ m/s
Solution: n = √16 = 4; v = c/4 = 0.75 × 10⁸ m/s.