Electromagnetic Waves
Kerala Board · Class 12 · Physics
Flashcards for Electromagnetic Waves — Kerala Board Class 12 Physics. Quick Q&A cards covering key concepts, definitions, and formulas.
What is displacement current and why was it introduced by Maxwell?
Answer
Displacement current is an equivalent current that flows due to a changing electric field, just like conduction current produces magnetic field. Maxwell introduced it to resolve the inconsistency in A
Write the mathematical expression for displacement current.
Answer
Displacement current: id = ε₀(dΦE/dt), where ε₀ is the permittivity of free space and ΦE is electric flux. For a capacitor with area A and electric field E: id = ε₀A(dE/dt). This equals the conduction
State the modified Ampere's law (Ampere-Maxwell law).
Answer
∮B⃗·dl⃗ = μ₀(i + id) = μ₀i + μ₀ε₀(dΦE/dt), where i is conduction current and id is displacement current. This law states that both conduction current and changing electric field produce magnetic field
List all four Maxwell's equations.
Answer
1. ∮E⃗·ds⃗ = q/ε₀ (Gauss law for electricity) 2. ∮B⃗·ds⃗ = 0 (Gauss law for magnetism) 3. ∮E⃗·dl⃗ = -dΦB/dt (Faraday's law) 4. ∮B⃗·dl⃗ = μ₀i + μ₀ε₀(dΦE/dt) (Ampere-Maxwell law)
What is an electromagnetic wave and how is it generated?
Answer
An electromagnetic wave consists of oscillating electric and magnetic fields perpendicular to each other and to the direction of propagation. It is generated by accelerated charges. The oscillating el
Write the mathematical expressions for electric and magnetic fields in an electromagnetic wave.
Answer
For a wave propagating in z-direction: Electric field: Ex = E₀ sin(kz - ωt) Magnetic field: By = B₀ sin(kz - ωt) where k = 2π/λ is wave vector magnitude and ω is angular frequency.
What is the relationship between electric and magnetic field amplitudes in an electromagnetic wave?
Answer
B₀ = E₀/c, where c is speed of light in vacuum. Also, the instantaneous relationship is B = E/c. The magnetic field amplitude is much smaller than electric field amplitude numerically due to the large
What is the speed of electromagnetic waves in vacuum and in a medium?
Answer
In vacuum: c = 1/√(μ₀ε₀) = 3×10⁸ m/s In a medium: v = 1/√(με), where μ is permeability and ε is permittivity of the medium. Speed in medium is always less than in vacuum.
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Sources & Official References
- Kerala Board of Public Examinations — keralapareekshabhavan.in
- National Education Policy 2020 — education.gov.in
Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.
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