1. Hypothesis → 2. Experiment → 3. Proof

Section § 9 · Wave Optics & Light Wavefront t = 0.00 s

Light Wavefront & Huygens–Fresnel Principle

Every point of a medium reached by a light wavefront becomes a source of secondary hemispherical wavelets, whose envelope forms the new wavefront at the next instant.

Question

A plane light wavefront passes from air (n_1 = 1.0) into optically denser glass (n_2 = 1.5) at an angle of incidence \alpha > 0. Why does the plane of the light wavefront bend toward the normal (\gamma < \alpha)?

Selected: Option B

According to Huygens' principle, as an oblique light wavefront reaches the interface, its left edge enters the glass first and emits secondary hemispherical wavelets that travel at a lower phase velocity v_2 = c/n_2. While the right edge travels v_1 \Delta t in air, the left edge travels only v_2 \Delta t in glass, rotating the wavefront envelope so that \sin\alpha / \sin\gamma = v_1 / v_2 = n_2 / n_1.

Formula

Energy balance E = 0.0 J

Kinetic E_k

0.0 J

Potential E_p

0.0 J

Heat Q

0.0 J

Fig. 9.1 . Light energy flux: incident, refracted, and reflected wavefronts

Equations

Parameters

Overlays

Force and velocity vectors Vector labels Trajectories and guides Wavefronts and particles

Velocity ($\vec{v}$)

Momentum / Projections

Gravity ($m\vec{g}$)

Normal / Tension / Pressure