Wave Propagation: Reflection, Refraction, and Diffraction
Waves exhibit unique behaviors when they encounter obstacles or boundaries.
Reflection, refraction, and diffraction are three fundamental phenomena that reveal the wave nature of light and other types of waves.
Wavefronts and Rays: Visualizing Wave Propagation
- To understand how waves propagate, physicists use two complementary concepts: wavefronts and rays.
- These tools help us visualize the direction and behavior of waves in two and three dimensions.
Wavefronts
Wavefront
A wavefront is an imaginary surface that connects points on a wave that are in phase (i.e., at the same point in their oscillation cycle).
Wavefronts are often depicted as lines or surfaces:
- In two dimensions, wavefronts appear as lines (e.g., concentric circles for ripples on water).
- In three dimensions, wavefronts form surfaces (e.g., spherical shells for sound waves).
- Consider a pebble dropped into a pond.
- The wavefronts are the circular ripples that spread outward, representing points where the water surface is at the same height.
Rays
Ray
A ray is a line drawn perpendicular to a wavefront, indicating the direction of wave propagation.
Rays are useful for visualizing how waves travel and interact with obstacles.
ExampleIn the case of light waves, rays show the path that light takes as it travels, reflects, or refracts.
Using Wavefronts and Rays Together
Wavefronts and rays provide complementary information:
- Wavefronts show the shape and phase of the wave.
- Rays indicate the direction of energy transfer.
When drawing wavefronts and rays, remember that rays are always perpendicular to the wavefronts.
Reflection: Waves Bouncing Off Surfaces
Reflection
Reflection occurs when a wave strikes a surface and bounces back into the original medium.
This behavior is governed by the law of reflection, which states that the angle of incidence is equal to the angle of reflection.
Note- The angle of incidence is the angle between the incoming wave and the normal (a line perpendicular to the surface).
- The angle of reflection is the angle between the reflected wave and the normal.
How Reflection Works
- Consider a beam of light hitting a mirror.
- The light wave approaches the mirror at a certain angle, called the angle of incidence.
- Upon striking the mirror, the wave reflects off the surface at an angle equal to the angle of incidence.
- Reflection occurs in many types of waves, including light, sound, and water waves.
- The smoothness of the surface determines the quality of the reflection.
- A smooth surface, like a mirror, produces a clear reflection, while a rough surface scatters the waves in different directions.
