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#medium properties

3 public questions tagged with this topic.

Production of EM Waves and Hertz Experiment

Why does the speed of electromagnetic waves in a medium depend on the medium’s properties?

**Hertz experiment** used induction coil connected to two rods with gap, spark produced oscillating charge, emitted EM wave, received by loop with gap sparking when E induced, measured wavelength by standing wave, demonstrated EM wave properties, validating Maxwell. The speed of electromagnetic waves in a medium is determined by the medium’s permittivity ( ε ) and permeability ( μ ), as v = (1/√(μ ε)) , which modifies the wave’s propagation characteristics. Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields Dependence on permittivity and permeability, illustrating EM wave transverse nature and Maxwell's displacement current concept.

Ref: NCERT > Physics Book > Electromagnetic Waves > Production of EM Waves and Hertz Experiment

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Displacement Current and Ampere-Maxwell Law

The velocity of light in a medium with permittivity \( \varepsilon \) and permeability \( \mu \) is:

**Displacement current** I_d = ε₀ dΦ_E/dt, Φ_E = ∫ E·dA electric flux (V·m), ε₀=8.85×10⁻¹² F/m, ensures continuity of current in charging capacitor where conduction current stops between plates, I_d equals conduction current in wires, 3 A conduction ⇒ 3 A displacement, maintaining Ampere's law ∮ B·dl = μ₀(I_c+I_d). As per Maxwell's equations, the velocity of light in a medium is v = (1/√(μ ε)) . Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields (1/√(μ ε)), illustrating EM wave transverse nature and Maxwell's displacement current concept.

Ref: NCERT > Physics Book > Electromagnetic Waves > Displacement Current and Ampere-Maxwell Law

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Doppler Effect

Which property of a medium is most critical for the propagation of longitudinal waves through a gas?

**Relative motion** changes effective wavelength encountered. For moving source approaching stationary observer, wavelength ahead λ' = (v - v_s)/f, so f' = v/λ' = f·v/(v - v_s) > f, basis for calculating apparent pitch shift in sound. Longitudinal waves in a gas rely on compressibility, quantified by the bulk modulus, which provides the restoring force for pressure oscillations, unlike shear modulus needed for transverse waves. Using v = fλ and standing-wave condition fₙ = n v/(2L) or v/(4L) as applicable, calculation yields Bulk modulus, illustrating frequency-length-speed interdependence and quantization by boundaries.

Ref: NCERT > Physics Book > Waves > Doppler Effect

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