Light & Optics Review

Normal Line

Terminology of Reflection

Incident Ray Reflected Ray

<i <r

<i = <r

1. <i is equal to <r

2. Incident ray, reflected ray and the normal all lie in the same plane.

Laws of Reflection

Mirror

Locating an image in Mirror

Size Smaller vs. Same vs. Larger

Attitude Upright vs. Inverted

Location Where the image is located

Type Real vs. Virtual

SALT

Incident rays entering to a “Cave” Concave = converging

Concave Mirrors - Rules

C VF

Principal axis

Image on SAME SIDE as object = REAL Image behind the mirror = VIRTUAL

Concave Mirrors – Real vs. Virtual Image

Object

REAL Image

VIRTUALImage

Simply use 2 of the rules

Concave Mirrors – Finding the Image

C VF

If object is at F = no clear image

Concave Mirrors – Finding the Image

F VC

Lines do not meet up

If object is between F and V = Virtual image

Concave Mirrors – Finding the Image

F VC

Incident rays”bouncing off a ball” Convex = diverging

Convex Mirrors - Rules

V F

Principal axis

C

Incident rays ”bouncing off a ball” Image is ALWAYS smaller and virtual

Convex Mirrors – Finding the Image

V F C

Bending of light when it travels from one medium to anotherIf SLOWING down when entering another medium

bend TOWARDS the normal

Normal LineIncident Ray <i

Medium A (Faster\)

Medium B (Slower) <R Refracted Ray

Refraction

If SPEEDING UP when entering the medium bend AWAY from the normal

Normal LineIncident Ray <i

Medium A (Slower)

Medium B (Faster)

<R Refracted Ray

Refraction

Either use: n = c . OR n = sin <i . v sin <R Example 1: Speed of light in air is 3.00 x 108 m/s. Speed of

light in salt is 1.96 x 108 m/s. Light enters from air to salt. Which way does the light bend? What is the index of refraction?

Calculating Index of Refraction (n)

Either use: n = c . OR n = sin <i v sin <R Example 2: Index of refraction of quartz is 1.46. If the angle

of incident ray from air is 600, what is the angle of refracted ray in quartz?

Calculating Index of Refraction (n)

ONLY occurs under 2 conditions:

1. Light is travelling more slowly in 1st medium than in 2nd medium (going from SLOWER to FASTER)

2. Angle of incidence is GREATER than critical angle

Total Internal Refraction

Normal Line

Air (FASTER)

Water (SLOWER)

Total Internal Refraction

Critical angle

F = principal focus F’ = secondary principal focus O = optical centre

Converging Lens - Rules

F’ 2FF

Principal axis

2F’ O

If Image is on the OPPOSITE SIDE of the lens from the object = REAL Image

If Image is on the SAME SIDE as object = Virtual Image

Converging Lens – Real vs. Virtual Image

REAL Image

ObjectVIRTUAL Image

Simply use 2 of the rules

Converging Lens – Finding the image

F’ 2FF2F’ O

The only time you’ll get VIRTUAL image with converging lens is when the object is between F’ and O

Converging Lens – Finding the image

F’ 2FF2F’ O

F = principal focusF’ = secondary principal focusO = optical centre

Diverging Lens- Rules

F 2F’F’

Principal axis

2F O

Always the SAME image characteristics no matter where the object is located: Smaller, upright, virtual, same side as object.

Diverging Lens- Finding the image

F 2F’F’

Principal axis

2F O

1 + 1 = 1

do di f

Object

Thin Lens Equation

F’ 2FF2F’ O

Image

do

f f

di

ho

hi

1 + 1 = 1do di f

do is always +

di is + for real image

- for virtual image

f is + for converging lens

- for diverging lens

Thin Lens Equation

M = hi = - di

ho do

h0 and h1 are:

+ when measured upward - when measured

downward

M is: + for upright image - for inverted image