Wave phenomena including reflection, refraction, diffraction Notes

What Are Wave Phenomena?

1. As waves travel, they often interact with their surroundings.
2. Waves do not always continue in straight lines without change.
3. When a wave meets a surface, boundary, or opening, its direction or shape may change.
4. These changes in wave behaviour are called wave phenomena.
5. The same wave phenomena occur for all types of waves, including sound waves and water waves.
6. The key wave phenomena are reflection, refraction, and diffraction.

Reflection Changes Direction By Bouncing From A Surface

1. Reflection occurs when a wave meets a boundary and returns to the original medium.
2. Reflection happens when a wave strikes a surface and bounces back.
3. The wave remains in the same medium after reflection.
4. Reflection occurs for all waves, including sound and water waves.
5. The reflected wave still carries energy.

The Law Of Reflection Uses Angles To The Normal

1. The direction of a reflected wave follows a clear and predictable rule.
2. The incident wave is the wave that approaches the surface.
3. The reflected wave is the wave that leaves the surface.
4. The normal is an imaginary line drawn at right angles to the surface.
5. Angles are measured between the wave direction and the normal.
6. The angle of incidence is equal to the angle of reflection.

$$\theta_i = \theta_r$$

Specular And Diffuse Reflection Explain Images Versus Glare

1. The nature of the surface affects how waves reflect.
2. Smooth surfaces produce regular reflection, where reflected waves remain parallel.
3. Rough surfaces produce diffuse reflection, where waves reflect in many directions.
4. Diffuse reflection spreads wave energy over a wider area.

Refraction Bends Waves Because Their Speed Changes

1. When a wave enters a new medium, its speed changes.
2. Refraction occurs because wave speed changes.
3. Refraction happens when a wave passes from one medium into another.
4. The wave changes speed in the new medium.
5. This speed change causes the wave to change direction.
6. Refraction occurs at the boundary between two materials.

What Changes During Refraction?

1. Wave speed changes when the medium changes.
2. Wavelength changes because wave speed changes.
3. Frequency remains constant because it is set by the source.
4. Energy continues to be transferred across the boundary.

Direction of Bending During Refraction

1. The direction in which a wave bends depends on whether it speeds up or slows down.
2. When a wave enters a medium where it travels slower, it bends towards the normal.
3. When a wave enters a medium where it travels faster, it bends away from the normal.

Refractive Index Quantifies How Much Light Slows Down

1. For light, the change in speed is often expressed using the refractive index $n$.
2. The refractive index of a medium describes how much a wave slows down.
3. A higher refractive index means the wave travels more slowly in that medium.
4. Refractive index has no units.

$$v = \frac{c}{n}$$

Bending Direction Depends On Whether The Wave Slows Or Speeds Up

1. If a wave slows down on entering the new medium, it bends towards the normal.
2. If a wave speeds up, it bends away from the normal.

Apparent Depth Is A Consequence Of Refraction

1. Refraction can make objects under water look closer to the surface than they really are.
2. Light from the object bends as it leaves the water, but your brain assumes light traveled in a straight line, so it places the image at a shallower (apparent) position.

Snell’s Law

1. Snell’s law relates the angles of incidence and refraction.
2. It applies when waves cross a boundary between two media.

$$n_1 \sin \theta_1 = n_2 \sin \theta_2$$

where:

1. n1,n2n_1, n_2n1​,n2​ are refractive indices
2. θ1\theta_1θ1​ is the angle of incidence
3. θ2\theta_2θ2​ is the angle of refraction

Diffraction Spreads Waves Out After Gaps And Around Edges

1. Diffraction describes the spreading of waves.
2. Diffraction occurs when waves pass through a gap or around an obstacle.
3. The wave spreads out after passing the gap.
4. Diffraction happens for all types of waves.
5. The amount of diffraction depends on wavelength and gap size.

Gap Size Compared With Wavelength Controls The Diffraction Strength

1. Diffraction is most noticeable when the gap size is similar to the wavelength.
2. If the gap is much larger than $\lambda$, the wave spreads only a little.
3. If the gap is about the same size as $\lambda$, the wave spreads out strongly (often almost semicircularly).
4. If the gap is much smaller than $\lambda$, the emerging wave can spread out in almost all directions, but less energy passes through.

Interference Connects Wave Behavior And Enables Noise Cancellation

1. Interference occurs when waves overlap.
2. Interference happens when two or more waves meet at the same point.
3. The waves combine according to the principle of superposition.
4. The resulting wave depends on how the wave displacements combine.

1. Constructive Interference

1. Occurs when waves meet in phase.
2. Crests meet crests and troughs meet troughs.
3. The resulting wave has a larger amplitude.

2. Destructive Interference

1. Occurs when waves meet out of phase.
2. A crest meets a trough.
3. The resulting wave has a smaller amplitude or may cancel out.