Wavefront and Huygens' principle — practice questions

Question 1 · difficulty L1 · recall

A wavefront is a surface joining points that have

• A. the same amplitude only regardless of phase
• B. zero frequency
• C. the same phase
• D. the same velocity direction only

Question 2 · difficulty L1 · understanding

According to Huygens' principle, every point on a wavefront acts as

• A. a perfect absorber
• B. a magnetic monopole
• C. a stationary mirror only
• D. a source of secondary wavelets

Question 3 · difficulty L2 · understanding

For a point source in a homogeneous isotropic medium, wavefronts are

• A. spherical
• B. always plane
• C. cylindrical only
• D. random surfaces

Question 4 · difficulty L2 · application

For a plane wave propagating in a uniform medium, rays are

• A. tangent to wavefronts
• B. normal to the plane wavefronts
• C. parallel to E only and not propagation
• D. randomly directed

Question 5 · difficulty L3 · application

Huygens' principle can reproduce the law of reflection by comparing

• A. only photon momentum with no wave construction
• B. charges on the mirror
• C. the envelope of secondary wavelets at the reflecting surface
• D. thermal emission from the mirror

Question 6 · difficulty L3 · application

Huygens' construction of refraction reflects the fact that wave speed

• A. is identical in all media
• B. becomes infinite at an interface
• C. depends only on amplitude
• D. changes across media with different refractive indices

Question 7 · difficulty L4 · analysis

A plane wavefront enters a slower medium obliquely. The refracted wavefront orientation changes so the ray bends

• A. toward the normal
• B. away from the normal
• C. along the interface always
• D. back into the first medium only

Question 8 · difficulty L4 · analysis

A spherical wavefront of very large radius can locally be treated as

• A. exactly a point
• B. approximately plane
• C. a magnetic field line
• D. a standing wave only

Question 9 · difficulty L5 · analysis

Two neighbouring points on one ideal wavefront differ in phase by

• A. π/2 necessarily
• B. π necessarily
• C. zero modulo 2π
• D. a random value

Question 10 · difficulty L5 · analysis

Why are rays and wavefronts complementary descriptions in geometrical optics?

• A. They are unrelated physical entities
• B. Wavefronts apply only to sound
• C. Rays must lie tangent to wavefronts
• D. Rays give propagation direction while wavefronts map equal-phase surfaces