Optics Mirrors, Lenses and Stuff

The Electromagnetic Spectrum

What uses to we make for different types of EM radiation? -radio -medical imaging -seeing -studying the universe -cooking our delicious food(microwaves)

The Electromagnetic Spectrum EM radiation is pretty crazy stuff—it exhibits wave-particle duality EM radiation is pretty crazy stuff—it exhibits wave-particle duality That means that you can think of light as being both a wave(Maxwell and others) and a particle(photon)(Newton and others) That means that you can think of light as being both a wave(Maxwell and others) and a particle(photon)(Newton and others) The way that you examine the light will determine which of the properties it demonstrates The way that you examine the light will determine which of the properties it demonstrates

Wave-Particle Duality

My Friend Roy G. Biv

Roy G. Biv hk5ICTI hk5ICTI hk5ICTI hk5ICTI

The Eye Humans(among other animals) are trichromats Humans(among other animals) are trichromats We have three types of cones; one optimised for blue, one for green and one for red We have three types of cones; one optimised for blue, one for green and one for red

Colour Addition -vision -vision

Colour Addition

Colour Subtraction

A—Red A—Red B—Red B—Red C--Black C--Black

Colour Why does the Sun appear yellow? Why does the Sun appear yellow? What colour would it appear in space? What colour would it appear in space?

Reflection Light travels in straight lines Light travels in straight lines How do you know this is the case? How do you know this is the case?

Law of Reflection

Images in Plane Mirrors Image seems to be the same distance “behind” the mirror as the object is in front Image seems to be the same distance “behind” the mirror as the object is in front Images are left-right inverted Images are left-right inverted

Describing Images S—size, bigger or smaller than object S—size, bigger or smaller than object A—attitude, upright or inverted A—attitude, upright or inverted L—location L—location T—type, either real(can be projected on a screen) or virtual T—type, either real(can be projected on a screen) or virtual

Fancy Mirrors Ooh la la

Concave Mirrors C is the centre of curvature F is the focal point Describe the image

Convex Mirrors Convex mirrors only produce virtual images.

Refraction Refraction is the bending of waves when they travel from one substance into another Refraction is the bending of waves when they travel from one substance into another The bending is caused because the wave changes speed in the new substance The bending is caused because the wave changes speed in the new substance And now for the famous students holding meter sticks demonstrating refraction demo And now for the famous students holding meter sticks demonstrating refraction demo

nding-light nding-light nding-light nding-light

Index of Refraction Materials in which lights travels more slowly are called optically dense Materials in which lights travels more slowly are called optically dense To compare how optically dense a medium is, we compare the apparent speed of light in the medium to the speed of light in the vacuum of space To compare how optically dense a medium is, we compare the apparent speed of light in the medium to the speed of light in the vacuum of space In space, c=3.0X10 8 m/s In space, c=3.0X10 8 m/s The ratio is called the index of refraction The ratio is called the index of refraction n will always be greater than 1—why? n will always be greater than 1—why?

Index of Refraction Ex) Diamond has an index of refraction of What is the apparent speed of light in diamond?

Snell’s Law n is the index of refraction and is physical property of the medium n is the index of refraction and is physical property of the medium A higher n, means that light travels more slowly through that medium A higher n, means that light travels more slowly through that medium sin is a trig ratio(from triangles) sin is a trig ratio(from triangles) The vertical line is called the normal

Snell’s Law Ex) Light travels from air into water at an angle of incidence of 30 o. If the n air =1 and n water =1.33, find the angle of refraction(the angle the light travels in the water) Ex) Light travels from air into water at an angle of incidence of 30 o. If the n air =1 and n water =1.33, find the angle of refraction(the angle the light travels in the water)

Total Internal Reflection What is going on in the diagram to the left? What is going on in the diagram to the left? When light travels into faster media, their rays refract AWAY from the normal When light travels into faster media, their rays refract AWAY from the normal At a special angle(special to the two media), called the critical angle, the ray will not be refracted but all its energy will be reflected internally At a special angle(special to the two media), called the critical angle, the ray will not be refracted but all its energy will be reflected internally

Total Internal Reflection What is the critical angle for light travelling from water, n=1.33, into air, n=1.00?

Lenses

Lenses A device that refracts light A device that refracts light What do we use them for? What do we use them for?

Lenses

Convex Lenses(Converging)

Convex Lenses

Rays through the optical centre do not refract Rays through the optical centre do not refract Rays parallel to the principal axis refract through the focal point Rays parallel to the principal axis refract through the focal point Rays through the secondary focus refract parallel to the principal axis Rays through the secondary focus refract parallel to the principal axis How many rays are needed to find the image? How many rays are needed to find the image?

Convex Lenses

Concave Lenses Notice that the focus is on the same side as the object. How is that different from convex lenses? Why?

Concave Lenses(Diverging)

Concave Lenses The ray rules for concave lenses are the same as for convex lenses but the rays diverge on the other side of the lens The ray rules for concave lenses are the same as for convex lenses but the rays diverge on the other side of the lens Your eye plays a trick on you and converges the rays on the same side of the lens as the object, creating a virtual image Your eye plays a trick on you and converges the rays on the same side of the lens as the object, creating a virtual image

metric-optics metric-optics

The Thin Lens Equation Relationship between the focal length of a lens and the distances from the lens to the object and to its image Relationship between the focal length of a lens and the distances from the lens to the object and to its image Does it remind you of another formula? Does it remind you of another formula?

Sign Conventions heights above the axis are considered “+”; those below, “-” heights above the axis are considered “+”; those below, “-” object distances on the same side as the light source are considered “+”; those on the opposite side “-” object distances on the same side as the light source are considered “+”; those on the opposite side “-” image distances on the opposite side to the object are considered “+”; those on the same side as the object “-” image distances on the opposite side to the object are considered “+”; those on the same side as the object “-”

Sign Convention Which values in the diagram are positive? Which values in the diagram are positive? h o, h i, d o Which negative? Which negative? didididi

The Magnification Equation Another(and I promise the last) relationship that exists for lenses is the magnification equation—it is a ratio of the h o to h i Another(and I promise the last) relationship that exists for lenses is the magnification equation—it is a ratio of the h o to h i

Questions 1) A diverging lens has an f of 29 cm. A virtual image of a unicorn is located 13 cm in front of the lens. Where is the unicorn located? 2) A tiny unicorn of height 8.4 cm is balanced in front of a converging lens. An inverted, real image of height 23 cm is noticed on the other side of the lens. What is the magnification of the lens? 3) A unicorn statue of height 53 cm produces a virtual image of 78 cm. The statue is located 1.3 m in front of the lens. What is the image distance?