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**7**

Section 35.6

Slide 42

The law of reflection can be derived from Huygens’s principle.

AB is a plane wave front of incident light.

The wave at A sends out a wavelet centered on A toward D.

The wave at B sends out a wavelet centered on B toward C.

AD = BC = c Δt

Section 35.6

Slide 43

Triangle ABC is congruent to triangle ADC.

cos g = BC / AC

cos g’ = AD / AC

Therefore, cos g = cos g’ and g = g’

This gives θ1 = θ1’

This is the law of reflection.

Section 35.6

Slide 44

Ray 1 strikes the surface and at a time interval Δt later, ray 2 strikes the surface.

During this time interval, the wave at A sends out a wavelet, centered at A, toward D.

Section 35.6

Slide 45

The wave at B sends out a wavelet, centered at B, toward C.

The two wavelets travel in different media, therefore their radii are different.

From triangles ABC and ADC, we find

Section 35.6

Slide 46

The preceding equation can be simplified to

This is Snell’s law of refraction.

Section 35.6

Slide 47

For a given material, the index of refraction varies with the wavelength of the light passing through the material.

This dependence of n on λ is called dispersion.

Snell’s law indicates light of different wavelengths is bent at different angles when incident on a refracting material.

Section 35.7

Slide 48

The index of refraction for a material generally decreases with increasing wavelength.

Violet light bends more than red light when passing into a refracting material.

Section 35.7

Slide 49

Since all the colors have different angles of deviation, white light will spread out into a spectrum.

Violet deviates the most.

Red deviates the least.

The remaining colors are in between.

Section 35.7

Slide 50

- Introduction to Light
- Light and Optics
- The Nature of Light
- Nature of Light – Alternative View
- Christian Huygens
- Confirmation of Wave Nature
- Particle Nature
- Dual Nature of Light
- Measurements of the Speed of Light
- Measurement of the Speed of Light – Roemer’s Method
- Roemer’s Method, cont.
- Measurements of the Speed of Light – Fizeau’s Method
- Fizeau’s Method, cont.
- The Ray Approximation in Ray Optics
- Ray Approximation
- Ray Approximation, cont.
- Reflection of Light
- Specular Reflection
- Diffuse Reflection
- Law of Reflection
- Law of Reflection, cont.
- Multiple Reflections
- Retroreflection
- Refraction of Light
- Refraction, cont.
- Refraction of Light, final
- Following the Reflected and Refracted Rays
- Refraction Details, 1
- Refraction Details, 2
- Light in a Medium
- The Index of Refraction
- Index of Refraction, cont.
- Frequency Between Media
- Index of Refraction Extended
- More About Index of Refraction
- Snell’s Law of Refraction
- Prism
- Huygens’s Principle
- Huygens’s Construction for a Plane Wave
- Huygens’s Construction for a Spherical Wave
- Huygens’s Principle and the Law of Reflection
- Huygens’s Principle and the Law of Reflection, cont.
- Huygens’s Principle and the Law of Refraction
- Huygens’s Principle and the Law of Refraction, cont.
- Huygens’s Principle and the Law of Refraction, final
- Dispersion
- Variation of Index of Refraction with Wavelength
- Refraction in a Prism
- The Rainbow
- The Rainbow, cont.
- Observing the Rainbow
- Double Rainbow
- Total Internal Reflection
- Possible Beam Directions
- Critical Angle
- Critical Angle, cont.
- Fiber Optics
- Construction of an Optical Fiber
- Fiber Optics, cont.

- Mechanics Lecture
- Geophysical Concepts, Applications and Limitations
- Radioactivity and Nuclear Reactions
- Static and Kinetic Friction
- Newton's Laws
- Newton's laws of motion
- Soil and Plant Nutrition

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