Physics Chp 15

• What happens when “light” hits a transparent material?

• Some of it reflects and/or refracts

• Refraction is the bending of light due to a change in it’s speed in the new material

• Index of refraction

• n = c/v 1 or greater

• While θi=θr for reflection it isn’t always true for refraction, it depends in n

• Snell’s Law

• n1sinθ1 = n2sinθ2

• So why do objects under the water look closer to the surface and farther away from us than they really are?

• Why does “light” refract?

• Lenses use refraction to redirect light

• Converging – brings the light towards the axis

• Diverging – directs the light away from the axis

• Ray Diagrams• Converging• 1 – from tip parallel then towards f• 2 – from tip thru f then parallel • 3 – from tip thru center

• Ray Diagram• Diverging• 1- parallel then away from f• 2- towards far f then parallel• 3 – thru center

• Thin lens equation

• Magnification equation

1 1 1

o id d f

i i

o o

h dmh d

• Signs

• f + converging

• do + on the left of lens

• di + on the right of lens

• m + for upright

• Sketch a ray diagram for a converging lens with focal length of 1 m and the object 0.5 m left of the lens and 0.2 m tall. Then calculate the distance of the image as well as it’s height.

1 1 10.5 1id

10.2 0.5ih

• Multiple Lenses image 1 = object 2

• Eye Type of lense?

• Near point – closest object distance that still gives a clear image

• Far point – farthest object distance that still gives a clear image

• Nearsightedness – far point issue, image in front of retina, use a diverging lens

• Farsightedness – near point issue, image is behind the retina, use a converging lens

• Microscope

• Telescope

• If n1 > n2 then there is an angle where θ2 = 90o

• Sinθc = n2 / n1

• θc is the critical angle

• If θ = θc then the “light” totally internally reflects

• Since each wavelength refracts differently prisms cause the rainbow from white light

• Also rainbows in the sky are caused by water droplets dispersing the light back towards us.

• Lens Aberrations – not a single focal pt

• Spherical aberrations – farther from the principal axis moves the focus

• Chromatic aberrations – different wavelengths refracting differently