Wave Behavior of Light Aim: How does light behave when it encounters a new medium?

Terminology Incident Ray/Angle – The ray/angle that originates in a medium and strikes the boundary of a new medium Reflected Ray/Angle – A ray/angle that has rebounded from a boundary Refracted Ray/Angle – A ray/angle that continues into the new medium that has a different density than the original medium Normal Line – An imaginary line that is perpendicular to the surface of two boundaries ALL angles are measured between the RAY and the NORMAL

Law of Reflection When a light ray hits a reflective surface, the reflected angle is equal to the incident angle Mirror Normal Line Incident Ray Reflected Ray θiθi θrθr Incident Angle Reflected Angle

Example #1 Determine the (a) incident angle, (b) the reflected angle and (c) the angle between the incident ray and the reflected ray Mirror Normal Line Incident Ray Reflected Ray θiθi θrθr 30° a) 60°b) 60°c) 120°

Specular vs. Diffuse Mirror Diffuse Reflection: All reflected rays go in various directions, resulting in a distorted or no image Specular Reflection: All reflected rays go in the same direction, resulting in a clear image

Refraction As light travels from one medium to another, light changes its SPEED, WAVELENGTH and DIRECTION However, the frequency NEVER CHANGES

Refraction Less Dense  More Dense Wavelength Decreases Speed Decreases Bends TOWARDS the normal More Dense  Less Dense Wavelength Increases Speed Increases Bends AWAY from the normal

Example #1 Use the diagram to the left to rank the different media from least dense to most dense n1n1 n2n2 n3n3 n4n4

Snell’s Law Index of Refraction for the FIRST MEDIUM Incident Angle Index of Refraction for the SECOND MEDIUM Refracted Angle

Example #2 An incident light ray in air hits a piece of flint glass at an angle of 50°. Determine the refracted angle Air Flint Glass n 1 = 1.00 n 2 = 1.66 θ2θ2 50°

Example #3 An unknown substance covers a piece of diamond. If the incident angle in the diamond is 25° and the refracted angle is 48.8°, what is the unknown substance? Unknown Substance Diamond n 2 = ??? n 1 = ° 25° Ethyl Alcohol

Critical Angle & Total Internal Reflection A phenomena where a light ray traveling from a more dense medium to a less dense medium refracts 90° to the normal, causing the refracted ray to travel along the border between the two media.

Other Useful Refraction Relationships Since the frequency of visible light NEVER CHANGES, the following relationship can be derived Subscript 1 represents values for the FIRST medium Subscript 2 represents values for the SECOND medium

Example #4 A ray of violet light with a frequency of 7.69×10 14 Hz travels through diamond at a speed of 1.24×10 8 m/s. Determine the wavelength of the light ray if it emerges into water

Diffraction The BENDING of a wave (light) around an obstacle or through a small opening

Diffraction Patterns Smaller openings cause MORE diffraction Longer wavelengths cause MORE diffraction

Dispersion The separating of the visible light spectrum through a PRISM

Summary Describe the Law of Reflection What is the difference between Specular and Diffuse reflection? Describe Refraction How does a light ray behave when… – It enters a DENSER medium? – It enters a LESS DENSE medium? How does light behave when it encounters an obstacle or small opening? What affects the amount of diffraction? Describe dispersion