SNC2D Grade 10 Academic Science – Physics Optics Notes

Thanks, Jennifer!

SNC2D Optics Review

Light
-is energy
-made of light particles called photons
-an electromagnetic wave
-travels at a very high speed
-travels in a straight line
-does not need medium to be transmitted
-properties of particles and EM wave (particle-wave duality) -study of light: OPTICS

Medium: a ny physical substance through which energy can be transferred
Radiation: method of energy transfer that does not require a medium, the energy travels at speed of light
V i s i b l e L i g h t : E M w a v e s t h a t t h e h u m a n e y e c a n s e e

Electromagnetic Wave
-a wave that has both electric and magnetic parts
-does not require medium
-travels at the speed of light
-use electromagnetic spectrum to classify these light waves
-visible spectrum is the continuous sequence of colours that make up white light
-colour sequence is the order of the rainbow (ROYGBIV, red being lower energy and increasing towards violet)
– l o w e s t t o h i g h e s t e n e r g y : r a d i o w a v e s , m i c r o w a v e s , i n f r a r e d l i g h t , v i s i b l e l i g h t , U V l i g h t , x – r a y s , gamma rays

Sources of Light
Indirect Light: n on-luminous objects reflect luminous object’s light (ex. moon) Direct Light: l uminous objects produce their own light (ex. sun)

Types of Light
Incandescent: h eated materials produce light (ex. lightbulb, molten metals, stove element) Electrical Discharge: e lectrical current flowing through gas produces light (lightning, northern lights)
Phosphorescent: materials called ‘phosphors’ absorb UV light from surroundings, STORE IT, emit energy as visible light (ex. glow in the dark toys)
Fluorescent: m aterials absorb UV light then IMMEDIATELY release it as visible light Chemiluminescence: mixture of chemicals produce light (ex. glow sticks)
Bioluminescence: c hemiluminescence in living organisms (ex. jelly fish, e.coli, fireflies) Triboluminescence: l ight produced by friction (ex. lifesavers)
LED (light emitting diode): electrical current flows through semi-conductors (ex. new Christmas lights)

The Ray Model
-light travels in a straight line
-light rays are the direction and straight path of the light
-using light rays to see the path of light is called g eometric optics
-matter can be transparent (see behind clearly), translucent (some light passes, can’t see behind clearly), or opaque (no light passes, matter absorbs light)

Reflection
-the bouncing back of light from any surface

Images: a reproduction of an object through the use of light
Mirror: a ny polished surface reflecting an image (has two parts:glass/reflective surface and reflective thin film/opaque side)
P l a n e : f l a t
Incident Ray: i ncoming ray that strikes the surface
Reflected Ray: ray that bounces off reflective surface
Normal: line perpendicular (90 degrees) to the mirror’s surface
Angle of Incidence: a ngle between incident ray and normal
Angle of Reflection: a ngle between normal and reflected ray

Laws of Reflection
1. The angle of incidence EQUALS the angle of reflection
2. The incident ray, reflected ray, and the normal all lie on the same plane

Specular Reflection:
-reflection on smooth shiny surface
-series of parallel rays hit the surface, their reflected rays are also parallel

Diffuse Reflection:
-light shines on surface that is not perfectly flat -many incident rays and angles of incidence -reflected rays are also different

Virtual Image: an image formed by light coming from an apparent light source; light is not arriving at or coming from the actual image location; cannot be projected on a screen

Images in Plane Mirrors
-use the laws of reflection
-distance from object to mirror is same as distance from image to mirror (image is located at same distance but reversed)
-object-image line is perpendicular to the mirror surface
-extrapolate the rays of light from the eye
-image is flipped horizontally and is in reverse order
-this is called LATERAL INVERSION (180 degree rotation of an object)

Properties of an Image

SALT
S: size of image (compared to object: same, smaller, larger)
A: attitude of image (orientation compared to object: upright, inverted, laterally inverted L: location of image

T: type of image; virtual, real

Centre of Curvature (C): centre of the sphere whose surface forms the mirror
Principal Axis: l ine going through the centre of curvature and the centre of the mirror
Vertex (V): p oint where the principal axis intersects the mirror
Focus (F): t he single point where all light rays parallel to the principal axis will be reflected off the mirror

Concave Mirror (converging)
-caves you in; inner surface/centre of mirror bulges away from you

Concave Mirror Rules:

  1. Any ray travelling parallel to the principal axis is reflected through the focal point (S TRAIGHT AND “F”)
  2. Any ray travelling through the focal point (F) is reflected parallel to the principal axis ( “F” AND STRAIGHT)
  3. Any ray travelling through the centre of curvature (C) is reflected back through the centre of curvature (T HROUGH “C”)

Converging/Concave Mirrors

Object

Image

Location

Size

Attitude

Location

Type

beyond C

smaller

inverted

between C and F

real

at C

same size

inverted

at C

real

between C and F

larger

inverted

beyond C

real

at F

no image

no image

no image

no image

inside F

larger

upright

behind mirror

virtual

Convex Mirrors (Diverging)
-sticks out at you, diverges away
-reflection is from the outer surface and the centre of the mirror bulges towards you

Same rules as Concave Mirrors 1. STRAIGHT AND “F” 2. “F” AND STRAIGHT 3. THROUGH “C”

Focus (F) and centre of curvature (C) is now behind the mirror as the VIRTUAL FOCUS

-brain extrapolates the rays behind the mirror, where they appear to converge
THE REFLECTED RAY CONTINUES BEHIND THE MIRROR AS A DOTTED LINE

IMAGE IS ALWAYS UPRIGHT, SMALLER, BEHIND THE MIRROR, VIRTUAL

Refraction
-happens between 2 media/materials
-light bends when it travels from one material into another

Angle of refraction: the angle between refracted ray and the normal

Rules for Refraction

  1. Incident ray, refracted ray , and normal all lie on the same plane-incident and refracted ray

    are on opposite sides of the line that separates the two media

  2. Light bends TOWARDS the normal when the speed of light in the second medium

    DECREASES

  3. Light bends AWAY from the normal when the speed of light in the second medium

    INCREASES

Index of Refraction

-the ratio of the speed of light in a vacuum to the speed of that medium

8 -Light travels the fastest in a vacuum [3.00×10 ]

-Mediums slow down light because it contains higher index of refraction

v = speed of light in given medium c = speed of light in vacuum
n = index of refraction

N=C/V

-i ndex of refraction can also be calculated using the sines of the angles: N=SIN<i/SIN<R

Gi ven→c=? v=? n=? Re quired → What to define? An alyze → Equation
So lve → Solve and answer So lution → Statement?

The Critical Angle
-angle of incidence that results in an angle of refraction of 90 degrees
-lies at 90 degrees or along the boundary between the two media
-the angle of incidence beyond which rays of light passing through a denser medium to a surface of a less dense medium are no longer refracted but totally reflected
-when the angle of incidence increases past the critical angle, the refracted ray will no longer exit the medium and it will reflect into the medium (total internal reflection)

Total Internal Reflection
-situation when the angle of incidence is greater than the critical angle -occurs when:

  1. light is travelling more slowly in the first medium than the second
  2. the angle of incidence is large enough that no refraction occurs in the second medium,

    instead, the ray is reflected back into the first medium

-n(1) must be greater than n(2)
-refracted ray bends away from normal
-eventually there is no refracted ray and only reflection

Lenses
-involve principle of refraction: light is refracted at the air to glass surface, travels through the lens and is then refracted again in the second air lens surface on the other side

-different lenses are made with the curvature of the lens
-can be drawn using ray diagrams or using the thin lens formula

Optical Centre (O): p oint at the exact centre of the lens
Principle Focus (F): point on the principle axis of a lens where the light rays parallel converge after refraction
Secondary Focus (F’): e quidistant to the principle focus bubt on the other side of the lens

Converging Lens: p arallel light rays converge through a single point after refraction or the light, THICKEST IN THE MIDDLE, THINNEST AT THE EDGE

F’ IS ON THE LEFT SIDE, SAME SIDE AS LIGHT SOURCE

Locating for Converging Lens & Diverging Lens -STRAIGHT AND F
-F’ AND STRAIGHT
-THROUGH O

Diverging Lens: p arallel light rays diverge after refraction from the lens, THINNEST IN MIDDLE, THICKEST AT THE EDGE

F IS ON THE LEFT SIDE, SAME SIDE AS ORIGIN

LIGHT RAYS BEING REFRACTED THROUGH THE LENS ARE CALLED EMERGENT RAYS

Thin Lens Equation (where the image is) f = focal length
do = distance of the object
di = distance of the image

Magnification Equation (size of image) m = magnification
hi = height of image
ho = height of object

Variable

Positive

Negative

do (object distance)

always

never

di (image distance)

real image (opposite side of lens)

virtual image (same side as lens)

ho (object height)

when upright/upward

when inverted/downward

hi ( image height)

when upright/upward

when inverted/downward

f ( focal length)

converging lens

diverging lens

M (magnification)

upright image

inverted image

Human Eye

Pupil: h ole where light enters the eye
Iris: c oloured ring of muscles that control the amount of light entering your eye by dilating or constricting your pupil
Cornea: c over on your eye that acts like lenses, directly over iris

Lens: l ens is an actual hard lens, focuses light as it passes through your pupil
Retina: m ade of light sensitive cells called photoreceptors, convert light to electrical signal transmitted to brain
P h o t o r e c e p t o r s : r o d s a n d c o n e s , d e t e c t l i g h t i n t h e e y e a n d t r a n s l a t e s i t t o n e r v e s i g n a l s s e n t t o t h e brain
Optic Nerve: c arries signals from retina to the brain to see
Sclera: e ye cover
Vitreous Humor: w hite part of the eye, fluid filled sac
Ciliary Body: m uscles that control the shape of the lens, we focus by ACCOMMODATION: to see objects that are closer our lens must get smaller and fatter, to see far our lens must be taller and

thinner

*The cornea and lens that focus the light entering our eyes produces an INVERTED image on our retina. The brain takes the signal information and translates it to an UPRIGHT image that we can see*

Hyperopia (far-sightedness)
-you can’t focus on near objects but can focus on far objects
-light rays would be focused on a spot behind the retina which is impossible so images become closer and blurry -CONVERGING lenses help correct the vision as it will cause the image to focus on our retina, bends light rays so image will focus on retina

Myopia (near-sightedness)
-you can’t focus on far objects but can focus on near objects
-light rays would be focused on a spot in front of the retina meaning the rays are diverging by the time they hit the retina

-DIVERGING lens can help correct vision as it will cause image to focus on our retina. bends light rays to focus on retina

Presbyopia
-age related vision impairment due to loss of ye elasticity from ciliary body, lens stiffens and unable to accommodate easily
-images form behind the retina, difficult to focus on nearby objects

Contact Lenses
-placed on cornea of eye
-shaped to correct near-sightedness or for cosmetics

Colour Blindness
-’colour normal’ see images as combinations of RGB light
-’colour deficient’ have inactive rods and cones of a particular sensitivity for RGB light