Chapter 16 – Mirrors and Lenses

what is the acceptation to "light travels along the shortest distance between two points; we believe it travels in a straight line"

if there's no obstructions or deviations

Out of all possible paths that light might travel to get from one point to another, it travels the path that requires the shortest time

Fermat's principle

The angle of incidence

The angle at which the light strikes the mirror; Angle made by the incoming ray and the perpendicular

Where does it appear that your reflection is standing?

Behind the mirror!

Obviously the light cannot be originating from behind a solid mirror, so why does your image appear to be located there?

An image located at a point where light does not actually originate is called a virtual image.

Convex mirror

curves outward : virtual images is smaller and closer (draw)

Diffuse reflection

When light strikes a rough or irregular surface and reflects in many directions; An undesirable circumstance is the ghost image that occurs on a TV set when TV signals bounce off buildings and other obstructions.

What happens to a big index

the index is more bent the refraction is

Illusions due to refraction:

When there is very hot heat there are waves in the dessert. It the hottest near the sand and you go up in is not as hot. --> mirages

;Objects such as the Sun seen through air are displaced because of atmospheric refraction.

Dispersion

;Refraction is greater on blue and it bends more --> when the emerge they spread spread out

;You disperse the colors showing the wavelengths

Life guard Ex:

if you're a lifeguard and a person is in trouble. You want to maximize time on sand and less on water. Light takes the path of the least (shortest) amount of time.

Principle of Least Time

Belief: light travels along the shortest distance between two points; we believe it travels in a straight line

Reflection

If you don't change medium there is no reflection. The condition of the mediums have to change it doesn't have to be materials

What happens when light interacts with matter electrons move?

When absorbing the light energy a remitted it can be remitted in a random direction.

Angle of reflection

equals the angle at which the light leaves the mirror; Angle made by the reflected ray and the perpendicular

Normal perpendicular to surface of the mirror at the reflection:

perpendicular to surface of the mirror at the reflection; Imaginary line perpendicular to the plane of the reflecting surface; Lies in the same plane as the incident and
reflected rays

Law of reflection: Flat or plane mirrors

Flat mirror reflects things straight back looking like it's going to the back of the mirror looking twice as far. Are brain believes this. You brain performs prospection of images

Virtual image

Is exact size as object, formed behind mirror, located at the position where the extended reflected rays converge

Virtual image: use and examples

Their common use is to allow human to look at themselves; they are to scale.

Car mirrors are different: main rear view mirror is a plane; the side mirror is not to scale and lets object appear larger.

Concave mirror

curves inward : virtual image is larger and father away (draw)

Light on the road EX:

Water fills the crooks and crannies in the road causing it to be harder to see

Rough road surface

because of diffuse reflection, see road ahead of car at night.

Wet road surface is smooth

because of less diffuse, reflection, difficult to see

Imagine a lifeguard can run faster on land than she can swim in the water What would be that path that takes the least time?

going in a diagonal path; you take more time on the sand to save the person in distress

Definition of refraction

When light bends going obliquely from one medium to another --> refection

Does light go faster in air or glass

Light goes faster in the air than glass. Air has a steeper slope which we can see

Refraction index need to have a #

= to 1 or more

What are three things Index refraction does

indicates how much the speed of light differs from its speed in a vacuum.
;indicates the extent of bending of rays.
;ratio of speed of light in a vacuum to the speed in a material

Index Refraction Formula

N = Speed of light in vacuum ÷ speed of light in material

Cause of Refraction

Bending of light when it passes one medium to another
Caused by change --> look at picture