UNIT 8 Light and Optics 1

Monday February 27 th 2 Light and Optics

TODAY’S AGENDA  Test Return  Thin Lenses Biconcave Lens  Total Internal Reflection Hw Practice B (all) p501  Reading Quiz Available Today UPCOMING…  Mon:Total Internal Reflection  Tue: Curved Mirror Lab  Wed:Interference and Diffraction  Thurs:Snell’s Law Lab Monday, February 27 3

Chapter 14 Light and Refraction

ConcepTest 35.4aRefraction I 1 air Parallel light rays cross interfaces from air into two different media, 1 and 2, as shown in the figures below. In which of the media is the light traveling faster? 1) medium 1 2) medium 2 3) both the same 2

ConcepTest 35.4aRefraction I 1 air The greater the difference in the speed of light between the two media, the greater the bending of the light rays. Parallel light rays cross interfaces from air into two different media, 1 and 2, as shown in the figures below. In which of the media is the light traveling faster? 1) medium 1 2) medium 2 3) both the same 2 Follow-up: air 12? Follow-up: How does the speed in air compare to that in 1 or 2? moving fastermoving slower

ConcepTest 35.5aGone Fishin’ I To shoot a fish with a gun, should you aim directly at the image, slightly above, or slightly below? 1) aim directly at the image 2) aim slightly above 3) aim slightly below

ConcepTest 35.5aGone Fishin’ I higher aimlower Due to refraction, the image will appear higher than the actual fish, so you have to aim lower to compensate. To shoot a fish with a gun, should you aim directly at the image, slightly above, or slightly below? 1) aim directly at the image 2) aim slightly above 3) aim slightly below

Total Internal Reflection Total internal reflection can occur when light attempts to move from a medium with a high index of refraction to one with a lower index of refraction Ray 5 shows internal reflection

Critical Angle A particular angle of incidence will result in an angle of refraction of 90° This angle of incidence is called the critical angle

Critical Angle, cont For angles of incidence greater than the critical angle, the beam is entirely reflected at the boundary This ray obeys the Law of Reflection at the boundary Total internal reflection occurs only when light attempts to move from a medium of higher index of refraction to a medium of lower index of refraction

Fiber Optics An application of internal reflection Plastic or glass rods are used to “pipe” light from one place to another Applications include Medical use of fiber optic cables for diagnosis and correction of medical problems Telecommunications

Atmospheric Refraction There are many interesting results of refraction in the atmosphere Sun’s position Mirages

Atmospheric Refraction and Sun’s Position Light rays from the sun are bent as they pass into the atmosphere It is a gradual bend because the light passes through layers of the atmosphere Each layer has a slightly different index of refraction The Sun is seen to be above the horizon even after it has fallen below it

Atmospheric Refraction and Mirages A mirage can be observed when the air above the ground is warmer than the air at higher elevations The rays in path B are directed toward the ground and then bent by refraction The observer sees both an upright and an inverted image

Lens and Mirror Aberrations One of the basic problems is the imperfect quality of the images Largely the result of defects in shape and form Two common types of aberrations exist Spherical aberration Chromatic aberration

Chromatic Aberration Different wavelengths of light refracted by a lens focus at different points Violet rays are refracted more than red rays The focal length for red light is greater than the focal length for violet light Chromatic aberration can be minimized by the use of a combination of converging and diverging lenses

The Rainbow A ray of light strikes a drop of water in the atmosphere It undergoes both reflection and refraction First refraction at the front of the drop Violet light will deviate the most Red light will deviate the least

The Rainbow, 2 At the back surface the light is reflected It is refracted again as it returns to the front surface and moves into the air The rays leave the drop at various angles The angle between the white light and the violet ray is 40° The angle between the white light and the red ray is 42°

Observing the Rainbow If a raindrop high in the sky is observed, the red ray is seen A drop lower in the sky would direct violet light to the observer The other colors of the spectra lie in between the red and the violet