232 questions on Electromagnetic Waves for NEET 2027. Below are 15 to try; tap a question to see its answer and explanation.
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Answer: (B) 54 MHz to 890 MHz
According to NCERT, television broadcast signals generally occupy the frequency band ranging from 54 MHz to 890 MHz. The standard AM band is 530 kHz to 1710 kHz, and FM band is 88 MHz to 108 MHz.
Answer: (D) 1.38 × 10³ W/m²
Average intensity is given by I = ε₀ c E_rms² = (8.85 × 10⁻¹²) × (3 × 10⁸) × (720)² = 2.655 × 10⁻³ × 518400 ≈ 1.376 × 10³ W/m² ≈ 1.38 × 10³ W/m².
Answer: (D) 4.0 × 10⁻¹⁵ N
Total incident power on the aperture is P = I × A = (1.5 × 10⁻⁶ W m⁻²) × (0.80 m²) = 1.2 × 10⁻⁶ W. For complete absorption, the radiation pressure is p_rad = I / c, and the radiation force is F = P / c = (1.2 × 10⁻⁶) / (3.0 × 10⁸) = 4.0 × 10⁻¹⁵ N.
Answer: (D) 7.4 A
The time constant is τ = R C = 5 Ω × 20 × 10⁻⁶ F = 0.1 ms. During discharging, the conduction current leaving the plates is equal in magnitude to the displacement current between the plates: i_d(t) = i(t) = (V₀/R) e^(-t/τ). At t = 0.1 ms = τ, i_d = (100 / 5) e⁻¹ = 20 × 0.37 = 7.4 A.
Answer: (D) Characteristic X-rays
Characteristic X-rays are emitted when high-energy electrons eject inner-shell electrons from heavy target atoms, prompting transitions of outer electrons into these vacancies. Gamma rays, by contrast, originate from transitions within atomic nuclei.
Answer: (A) (a) and (b) only
Statements (a) and (b) are correct: welding arcs emit intense ultraviolet light that can damage eyes (arc eye), so special dark glass filters are used; infrared lamps deliver heat to relax strained muscles. Statement (c) describes the production of X-rays, not gamma rays (gamma rays originate from nuclear transitions). Statement (d) is incorrect because the ionosphere is transparent to a wide band of radio frequencies (the radio window), allowing radio astronomy.
Answer: (A) Both Statement I and Statement II are correct
Ultraviolet light has very short wavelengths, allowing high spatial precision, which is utilized in excimer lasers for LASIK corneal surgery. UV radiation also exhibits germicidal properties, making it standard in commercial water purifiers.
Answer: (B) (2/3) ε₀ α A t
The displacement current density is J_d = ε₀ (dE/dt) = ε₀ (2α t). The displacement current through a cross-sectional area of A/3 is therefore i_d = J_d × (A/3) = (2/3) ε₀ α A t.
Answer: (C) 120 nT
B₀ = E₀/c = 36/(3 × 10⁸) T = 120 × 10⁻⁹ T = 120 nT.
Quick tip: B₀ = E₀/c, so the magnetic field is tiny in tesla.
NCERT Class 12, Chapter 8
Answer: (D) E⃗ = E₀ sin(kx - ωt) ĵ, B⃗ = B₀ sin(kx - ωt) k̂
For propagation in the +x-direction, the wave vector must satisfy Ê × B̂ = î. Here, ĵ × k̂ = î, and both fields oscillate in phase with identical argument (kx - ωt). Also, E and B must be mutually perpendicular and perpendicular to the direction of propagation.
Answer: (C) Microwaves < Infrared < Yellow light < X-rays
The momentum of an electromagnetic photon is given by p = h / λ = hf / c. Therefore, momentum is directly proportional to frequency. The correct ascending order of frequency is Microwaves < Infrared < Yellow light < X-rays, which corresponds identically to the ascending order of photon momentum.
Answer: (B) 0.030π A
In a capacitor, the displacement current equals the conduction current at every instant. The peak current is I₀ = V₀ / X_C = V₀ ω C = 150 × (100π) × (2.0 × 10⁻⁶) = 3 × 10⁻² π A = 0.030π A.
Answer: (A) Current
The term ε₀ (dΦ_E / dt) represents the displacement current. Since it is a form of current, its dimensional formula is [A] (or [M⁰ L⁰ T⁰ A¹]), which is the same as electric current.
Answer: (B) They penetrate deeply through packaging to eliminate microbes without raising temperature
Gamma radiation has exceptional penetrating capability and destroys microorganisms, spores, and bacteria by damaging their cellular DNA. Because this process eliminates pathogens without generating heat (cold sterilization), heat-sensitive foods and sealed packaging remain structurally intact.
Answer: (C) Velocity
In Maxwell's theory, the speed of light in vacuum is given by c = 1 / √(μ₀ε₀). Therefore, the dimensional formula of 1 / √(μ₀ε₀) is [L T⁻¹], which is identical to velocity.