Chapter 18: Refraction and Lenses Pre-Class for Tuesday 4-10-12 In terms of light transmission, what is the difference between mirrors and lenses?

Refraction Definition: bending of light as it passes from one material to another Cause: light travels slower through more optically dense materials The optical density is measured by the index of refraction (n), which is the ratio of the speed of light in a vacuum (c) to the speed of light in that material (v) n = c / v

n1sinq1 = n2sinq2 Snell’s Law Describes how light behaves when passing from one material to another Light passes through an object, but is deflected off its original line Amount of refraction is based on the object’s optical density and incident angle Incident ray Normal Refracted ray n1sinq1 = n2sinq2

Total Internal Reflection Light attempts to pass from one material to another Light must be traveling from a more dense to a less dense material If the incident angle is larger than the critical angle (qc), then light is reflected Law of Reflection applies (qi=qr) sin qc = n2/n1

Pre-Class Wednesday 4-11-12 What causes a rainbow?

3 TYPES OF LENSES PLANE CONVEX CONCAVE flat lens (window) always gives a real image CONVEX curved towards the object (symmetric on both sides) gives virtual or real images CONCAVE curved away from object (symmetric on both sides)

1/f = 1/di + 1/do LENS EQUATION f : focal length di : distance to image from lens do : distance to object from lens

M = hi / ho = - di / do MAGNIFICATION M : magnification hi : height of image ho : height of object di : distance from image to lens do : distance from object to lens

S I G N S If di is negative, virtual image This Way If di is negative, virtual image If di is positive, real image If M is negative, inverted image If M is positive, upright image rule of thumb: real images are what we expect, so they are positive (light passes through lens) remember: just because M is negative does not mean it is smaller, the sign is for orientation only F=m a No, this way

Ray Diagrams for Lenses // OA, thru f1 Thru f2, then // OA Thru center of lens Note: use refraction line and not actual lens surface.

HW CH 18 67. 1.33; water 69. 25.4o; 28.9o 70. 1.24x108 m/s 71. 24.4o 73. 53o, shallower 75. 1.96x108 m/s; 1.99x108 m/s 78. 28o; 32o; 53o 82. 39.3 cm 83. 10 cm 84. 14 cm 86. -1.5 cm 92. 35 mm, do is infinity 93. 60 mm, -5, -20 mm, -10 94. 21 cm, -0.494 cm, inverted; -324 cm, -40 cm, inverted; -4 100. 0.19 mm

Pre-Class Thursday 4-12-12 Which color of light travels the slowest through a material? Red Green Yellow Violet

Optical Devices

Ch19: Interference and Diffraction Diffraction is the scattering of light from a surface. Incoherent light: light that travels in all directions with circular wavefronts Coherent light: light that travels in one direction with linear wavefronts Sunlight or light bulb Laser or collimated beam

One piece of paper per group. Be sure everyone’s name is on it. Practice Problems Complete the following four: p487 #1-4 Choose three of following: p496 #15-17 p497 #20-23 One piece of paper per group. Be sure everyone’s name is on it.

Lenses Activity For each person, find the position for each lens that produces a sharp, clear image. Repeat for 2 lenses together Your name Type of lens Lens to eye M Upright or inverted both Lens to lens

Pre-Class Wednesday 4-15-09 What type of lens is in your eye? Hint: there are only three possibilities.

What is the smallest value that the index of refraction can be? Pre-Class Thursday 4-16-09 What is the smallest value that the index of refraction can be?

LENS LAB Materials: Objective: Procedures: meter stick, optical bench kit, lenses Objective: Find the focal length for each lens Procedures: Fill-out the chart on the next slide Draw ray diagrams for each different lens Repeat step 1 as time allows for a different lens

FILL-IN CHART NOTE: Be sure image is sharp and clear. Look for it on the correct side (real or virtual image).