JEE Main 2023 · 29 January · evening · Single correct · +4 / −1
Given below are two statements :
Statement I : Electromagnetic waves are not deflected by electric and magnetic field.
Statement II : The amplitude of electric field and the magnetic field in electromagnetic waves are related to each other as E₀ = √((μ ₀)/(ε ₀)) B₀.
In the light of the above statements, choose the correct answer from the options given below :
- (a) Both Statement I and Statement II are true
- (b) Statement I is true and Statement II is false
- (c) Both Statement I and Statement II are false
- (d) Statement I is false but Statement II is true
Answer and solution
Answer (b) Statement I is true and Statement II is false
Solution
Physics sir · 4 steps
Fields push only on charges, and E₀/B₀ has to be a speed, which is c.
- Statement I. Electric and magnetic fields exert force only on charges, through F⃗ = qE⃗ + qv⃗ × B⃗. An electromagnetic wave carries no charge, so q = 0 and the force is zero. The wave goes straight through, so Statement I is true.
- Correct relation. In an EM wave the two field amplitudes are linked by the wave speed, and that speed is fixed by μ₀ and ε₀.
E₀ = cB₀ = 1/√(μ₀ ε₀) B₀
- Check Statement II. Statement II uses √(μ₀/ε₀) instead. That quantity is about 377 Ω, the impedance of free space, not a speed. Since E₀/B₀ must have units of m s⁻¹, Statement II is false.
- So. Statement I is true and Statement II is false, which is option (b).
The idea to keep. Remember E₀ = cB₀ with c = 1/√μ₀ε₀. If you see √(μ₀/ε₀), that is about 377 Ω, a resistance, not a speed.
Answer from the NTA final answer key. Solution by PrepWiser.