Optics Gabrielle DePetro Amy Chang Tiffany Chau

Introduction to Optics Optics- study of how light behaves Speed of light- 3 x 10^8 m/s Speed of sound- 340 m/s Light is both a wave and a particle – Wave: can undergo destructive interference, refraction, diffraction – Particle: can travel through a vacuum

Reflection Reflection- the return of a wave back to its original medium Law of Reflection- states the angle of incidence and the angle of reflection are equal to each other Angle of Incidence- between the incident ray and the normal Angle of Reflection- between the reflected ray and the normal Normal- imaginary line perpendicular to a surface Angle of Incidence = Angle of Reflection

Reflection and Mirrors Mirrors produce only virtual images Virtual image- appears to be in location where light does not really reach Eye cannot tell difference between object and virtual images Image distance is same behind mirror as object distance is in front of it Image and Object are the same size

Refraction Refraction- bending of a wave as it crosses the boundary between two media at an angle Direction of light rays change because of refraction Causes of refraction: – Changes in speed of light crossing from one medium to another – Variations in temperatures and densities of same medium

Refraction and The Normal Depending on what medium they enter, light rays bend towards or away from the normal If light enters a medium in which it travels from: – Increasing to Decreasing speed, then rays bend TOWARD the normal – Decreasing to Increasing speed, then rays bend AWAY from the normal

Snell’s Law and Refraction

Critical Angle Critical angle- incident angle that causes the refracted ray to skim right along the boundary of a substance Produces an angle of reflection of 90° Only exists when light is attempting to penetrate a medium of higher optical density than it is currently traveling in If the angle of incidence exceeds the critical angle, the ray is completely reflected and does not enter the new medium

Total Internal Reflection Occurs when light attempts to pass from a more opticslly dense medium to a less dense medium at an angle greater than the critical angle There is no refraction, only reflection Used for fiber optics

Lenses Lens- piece of glass or plastic that refracts light Lenses change the path of light A light ray bends as it enters and leaves glass Lenses form an image by bending parallel rays of light that pass through it Light passing through certain shapes increases or decreases image size and distance compared to the object being viewed Focal Length- distance between center of lens and its focal point

Converging Lenses Converging = Convex Thicker in the middle Causes rays that are initially parallel to meet at a single point Focal point- point at which beam of light parallel to the principal axis converges Any incident parallel beam converges to a point on the focal plane Lens has 2 focal points and 2 focal planes Key features- principal axis, focal point, focal plane

Diverging Lenses Diverging = Concave Thinner in the middle Rays of light appear to originate from a single point Incident beam of light parallel to the principal axis is diverged Focal point- point at which light rays appear to originate from

Ray Diagram Rules Ray diagrams show the principal rays that can be used to determine the size and location of an image An arrow represents the object and one end is on principal axis To locate position of image, know the paths of 2 rays from a point on the object 3 Rules: – Ray parallel to principal axis passes through the focal point on the opposite side – Ray passing through the center of the lens that is undeflected – Ray through the focal point in front of the lens, emerges parallel to principal axis after refraction

Image Formation Type of image formed depends on the shape of the lens and the position of the object Magnification- when the use of a lens allows an image to be observed through a wider angle than would be observed without the lens Magnifying Glass- converging lens that increases the angle of view and allows more detail to be seen Magnification Equation: -image size/object size

Images Formation FOR CONVERGING Object is beyond focal point of converging lens: – Real image, inverted – Slightly beyond focal point  image is far away – Far from focal point  image is nearer Object is between focal point and lens: – Virtual image, magnified, farther from the lens than the object, right- side up FOR DIVERGING No matter how far or near the object is: – Virtual, right-side up, smaller than the object SUMMARY For all Real Images, image and object are on opposite sides of the lens For all Virtual Images, image and object are on same side of the lens

Multiple Choice Review 1.Convex lenses are… A)Convergent B)Divergent C)Mirrors D)Polarized 2. The image formed my concave lenses is always…. A)Real and Inverted B)Real and Upright C)Virtual and Inverted D)Virtual and Upright

3. For an object with d ₒ = 12m and focal length = -4m, what is the distance of the image? A)0.1m B)-3m C)-30m D)10m 4. ________ is an optical device that works by reflection and _______ is an optical device that works by refraction. A)Mirror, lens B)Lens, mirror C)Mirror, mirror D)Lens, lens

5. A concave lens is _______ and _______. A)Convergent, magnifies B)Convergent, reduces C)Divergent, magnifies D)Divergent, reduces 6. Nearsightedness can be corrected by… A)Convex lenses B)Convex mirrors C)Concave lenses D)None of the above

7. Calculate the critical angle for light going from water into air A)4.87° B)48.75° C)487.53° D)90° 8. (In the image below) As the image is moved from the red arrow to the green arrow it… A)is closer and increases in size B)is closer and decreases in size C)is farther and increases in size D)is farther and decreases in size

9. If an object is 8m from a lens and produces an image 4m from the lens, what is the magnification factor, M? A)-0.5 B)0.5 C)-0.05 D) The angle of reflection is 30°. What is the angle of incidence? A)30° B)60° C)90° D)150°

Answers ANSWERS: 1) A 2) D 3) B 4) A 5) D 6) C 7) B 8) C 9) A 10) A