Light travels through the path between two points in space that takes the shortest time!! x A B X X

Starting from A, make one touch at the wall and finish at B. Which path takes the shortest time? θ θ x A x B

Reflection and Mirrors qi = qr qi qr Law of reflection Specular Reflection Diffuse Reflection

Who has the better chance to save this drowning guy? Pam Anderson David Hasselhoff Jeremy Jackson Pamela Anderson People run faster on sand than swim in water!

Refraction Bending of light at the interface between two different media A air water B Light travels slower in water than in air.

Ex 29-1 A light ray emitted from a point source is reflected from two flat mirrors as shown in the figure. What is the angle A? 45° 30° (180 - 30 - 45)° 60° 30° A 45° 45°

Q1 A light ray emitted from a point source is reflected from two flat mirrors as shown in the figure. What is the angle A? 45 30 60 75 A 30°

OBJECT IMAGE Optical Components Mirrors (Reflection) Lenses (Refraction) OBJECT IMAGE Every object is considered as a collection of point light sources. An image is formed at the converging point of the rays passed through optical components. Optical Components Ray Diagram

Some Definitions parallel rays: a collection of rays propagating in parallel light coming from a point source infinitely far away (e.g. sunlight) focal point: point where the parallel rays (along the optical axis) converge after passing through a specific optical component. f focal length (f): distance from the optical component to the focal point. object length (p): distance from the optical component to the object. image length (q): distance from the optical component to the image.

(you trace at least two rays to form a converging point) optical axis: symmetry axis of an optical component. Focal point should be on the optical axis. Rules for Images Trace principle rays from one end of an object or a point source. (you trace at least two rays to form a converging point) Follow the rules of a specific optical component when the rays pass through the component. Continue to trace the rays until they converge at a point. It not make imaginary extension of each ray to the other direction to find a converging point.

We never know that the path of light rays coming into our eyes has been modified by optical components. We perceive the light as coming from the virtual image. VIRTUAL IMAGE q p Image forms at the point where the light rays converge. When real light rays converge  Real Image When imaginary extension of L.R. converge  Virtual Image Only real image can be viewed on screen placed at the spot.

p q IMAGE VIRTUAL For a plane mirror: p = q

p = q No mirror at this point  Cannot see the image!

To be able to see the whole body we do not need mirror below red line! p q To be able to see the whole body we do not need mirror below red line!

Q2 I am standing 2 m away from a vertical plain mirror. When I see the image of myself, how far is it from me? 2 m 4 m 1 m Infinitely far