Science Grade 10 - Optics

Two types of Lenses

Convex or diverging lens, thickest in the middle
Concave or converging lens, thinnest in the middle

Metric Prefixes and Symbols

tera: 10^12 T
giga: 10^9 G
mega: 10^6 M
kilo: 10^3 k
hecto: 10^2 h
deca: 10^1 da
base unit 10^0
deci: 10^-1 d
centi: 10^-2 c
milli: 10^-3 m
micro: 10^-6 u
nano: 10^-9 n
pico: 10^-12 p

What is Optics?

Optics is a branch of physics that studies the behavior and properties of light including its interaction with matter and the construction of instruments that use or detect it

What is Light?

Light is a form of Energy
In a vacuum, light travels at the constant speed of 3.0 x 10^8 m/s

Two Models of Light

- Newton and Einstein (1666-1915)
- Particle Theory of Light
- Huygens and Young (1800/1803 - 1690)
- Wave Theory of Light

Particle Model

Light is interpreted as a stream of tiny particles which we call photons

Wave Model

Light is interpreted as waves of energy

Wave/Particle Duality

- Physicists believe that light can behave as both a particle and wave
- Neither model can fully describe the observed behavior
- In Grade 10 science, we interpret light as waves because this best explains the phenomena we can see at our scale

What is visible light composed of?

Electromagnetic waves

What is a wave?

A wave is a disturbance that transfers energy from one point to another without transferring matter

What can "Light Waves" do?

They can move through empty space, but can be emitted or absorbed by matter

Other forms of energy that moves in waves

Radio, UV, X-Rays

Properties of Waves

Crest: Highest Point in a wave
Trough: Lowest point in a wave
Rest Position: Level without any waves
Amplitude: Is the height from the rest to the crest or to the trough
- Larger amplitude: more energy
- Lower amplitude: less energy
- Lambda, distance from one aspect of a wave to the next similar aspect on the wave measured in meters

Frequency (f)

f = waves/seconds
- the number of the waves each second
- measured in Hertz (Hz) per second

Period (t)

t = seconds/waves
- Period of a wave is the time taken for one complete wave to pass a point
- Measured in seconds (s)

Frequency and Periods

- If you mow a lawn twice a month (frequency)
- Takes you one hour to mow the lawn (period)
- Frequency and Period are inversely related
- f = 1/t --> t = 1/f

Frequency and Wavelength

- As frequency increases, wavelength decreases
- Frequency is inversely proportional to wavelength

Wave Equation

v=fλ, f=v/λ, λ=v/f

Electromagnetic Spectrum (EM)

Each type of electromagnetic wave has a distinct wavelength
It is the wavelength that determines the type of electromagnetic wave or the colour of visible light
They do not require a medium in order to travel

Classification of Waves by Energy

- Radio
- Microwave
- Infrared
- Visible
- ROY G BIV
- Ultraviolet
- X-ray
- Gamma Ray

Ionizing radiation

Causing chemical reaction that can damage or kill cells, enough energy to create ions

What does white light consist of?

White light consists of ROY G BIV
slowest vibration is red and the fastest is violet
speed increases as you go from red to violet
there is more bending of light as you go from red to violet

Black Light occurs when...

It occurs when all of ROY G BIV is absorbed in an object

WHich wavelengths are ionizing?

X-rays and Gamma rays

VIsible Light

violet: 4.0 x 10^-7
red: 7.0 x 10^-7
The part of the EM spectrum that we can see
Colours correspond to waves with different wavelengths

Longest wavelengths

- Shorter wavelength equals crater energy electoral magnetic radiation
- gamma rays x-rays in UV are damaging to human body
- wavelength of x-rays equals 1 x 10^-9 m

Shortest wavelength

Less energy of electromagnetic radiation
not harmful to human body, non-ionizing
radio microwaves infrared are commonly used in technology Wavelength can start from 1 to 100 m and can go to kilometers

Luminous

Objects that can produce and emit light and they can convert other forms of energy into light energy

Non-luminous

Objects that do not produce light and they reflect light from other sources

Incandescent

Light caused by heating that is extremely inefficient 5% is converted into light 95% is converted to heat
Example lightbulb: electric current passes through filament and heats it to a high temperature to produce light

fluorescent

Light emitted by object exposed to electromagnetic radiation Electric current excites the gas Mercury vapor and releases UV (electrical discharge) phosphorus absorbs UV phosphor radiates light (fluorescent)

Phosphoresense

Light produced by light the materials store energy from a source of light and emits it slowly over a long period of time

Triboluminescence

Light generated through the breaking of chemical bonds in a material when it is pulled apart ripped scratched crushed or rubbed

States of matter

Solid
liquid crystal, like calculator display
liquid
gas
plasma, candle flame or mercury vapor in fluorescent light

Bioluminescence

Production of light through a living organism

Electric discharge

Electric current passing through a gas and producing light

Electroluminescence

A material emits light when electric current is passed through
More efficient than incandescent and fluorescent lights 95% light 5% heat

Organic light emitting display

Light source organic carbon-based molecules that use an electric current to produce light It is thinner and lighter than LED

Plasma display

Each color is a tiny fluorescent light different phosphor different colour RGB

Liquid crystal display

1. White light shines behind liquid crystal
2. RGB filters in front of the crystal to give off color

what is the ray model of light

A way of interpreting light that is useful for describing and predicting the behavior of light when it interacts with flat and curved mirrors with prisms and with various kinds of lenses

Properties of light EM radiation

Reflect, refract and disperse

Ray model light

Light moves in straight lines and they show direction of light. Ray diagrams are used to show paths. Ray is a single unit of light that is drawn as a single straight marked by an arrow the direction of the arrow indicates the direction of motion of the EM wavefront (90° to it). A beam is a light and a bundle that contains many parallel rays of light all moving the same direction in this way we can illustrate the intensity of the light rays. Light rays can be parallel - traveling in the same direction, diverging - spreading away from each other and converging - moving towards a single point. Light travels in a straight line until the ray or wave hits something and interacts with it. Linear propagation - from source to the sink. Light rays converging and diverging.

What happens when light hits something and interacts with it?

It can absorb - light is stored by the substance, transmit - light passes through the material and reflect dash light bounces off the substance.

Types of material

transparent, translucent, opaque

Shadows

Umbra is where all the light is blocked by shadowing object, penumbra is a region around the umbrella where the light is only partially blocked occurs when the lights work is larger than a single point.

If all the lights are blocked and shadows have sharp edges but if some light is blocked shadow is blurry more light rays are blocked bigger shadows fewer light rays are blocked smaller shadows. Shadow size depends on the distance from the light source.

Light reflection

In a regular reflection the light rays try to smooth surface and reflect in the same direction staying parallel to one another, when light rays reflect off a rough or uneven surface they do not remain parallel but they are scattered in different directions resulting in a diffuse reflection.

Curved mirrors

Concave - converging occurs inward like the inner part of a circle, convex- diverging curves like the exterior of a circle of sphere.

The center of curvature is the center of the spear whose surface forms occurred in the mirror. The principal axis of the mirror is the line going to the center of curvature and the center of the mirror. The principal axis intersects the mirror at 90° and is normal to the surface. The vertex is the point where the principal axis intersects the mirror. Light rays that are parallel to each other will reflect off any part curve and pass through the same spot. This is called a focus The focus is halfway between the vertex and the center of curvature.

concave mirrors

Center bulges away. Causes parallel light rays approaching it to converge or meet at the focal point. Focus is on the same side as the object. To locate the image of an object in front of a converging error you need to draw at least two incident rays from the tip of the object.

convex mirrors

The mirror has the center pointing out. In a convex mirror the location of the focus and curvature are located behind the mirror. Diverging mirrors have a wide field of view that means that the mirror reflects light rays from a wide area.

What is refraction

Refraction is the bending of light as it passes from one medium into another. It is caused by a change in the speed of light which varies in each medium depending on the optical densities Remember light travels in straight lines in a given medium. It is when it moves from one medium to the next that the bending occurs.

how does light move in refraction?

Light only moves from less dense medium to more dense medium.

Index of Refraction Formula

n=c/v, where n is the index of refraction, c is the speed of light and v is the speed of light in that medium.

rules for refraction

when the light ray travels from one optically dense medium such as prism glass or water into a less optically dense one such as hair above the angle of incidence called the critical angle refraction becomes geometrically impossible and so reflection occurs instead.

Total internal reflection and dispersion

When life stays within a medium rather than passing from one medium into another, as light passes from a dense medium the refracted ray bends away from the normal line, as the angle of incidence increases the angle of refraction also increases until the point where it can't any longer.

Tir and critical angle

At the certain angle incidents the refracted angle is 90° the refractive ray travels at the interface of the two mediums This incident angle is called the critical angle, if the angle of incidence increases any further no more refraction is physically possible instead than a ray can only be reflected back internally to the optically denser medium.

The critical angle

The critical angle is the incident angle at which the light refracts along the boundary, total internal reflection occurs when light cannot refract and so bounces back into the optically denser medium occurs when the incident angle starts to exceed the critical angle.

TIR and refraction applications

fiber optic cables, dispersion rainbows, dispersion diamonds, total internal reflection mirages, total internal reflection magic tricks.

Fiber optics

Fiber optics work by total internal reflection, information traveling in the form of light is able to move around the earth very fast using fiber optics, optical fiber usually made up of glass tube as thin as human hair which light cannot escape, glass has a higher index of refraction that the surrounding medium the light is completely reflected inside.

Dispersion

Refraction of white light into separate colors, different colors of light travel at different speeds in glass and so have a different "n" value is why each color bends it's own angle moving between media.

Light dispersing in thousands of raindrops makes rainbows, light dispersing within the diamond is what gives any diamond it sparkle.

Mirages

Both total internal reflection and refraction play a role informing a mirage, a mirage is a image of a distant object produced as light refracts through air or different densities, since the light rays pass through layers of air with progressively lower indices of refraction eventually the light is total internally reflected.

Law of reflection

Angle of incidence equals angle reflection, a line at 90° to a plane is called a normal line. Everything must be in the same plane, angles are measured from the normal, normal is perpendicular to the point of incident.

Two types of reflections

Regular reflection is that incident rays from a single light source are parallel and identical when the parallel rays strike a flat surface the reflected rays are also parallel and identical.

Diffuse reflection incident rays directed that an irregular surface they will have different incident angles the reflected rays will be reflected in many directions.

Types of images

Real image, image that can be projected on a screen and it is always inverted on the same side of the mirror.

Virtual image, images which cannot be visually projected on a screen formed by light coming from an apparent not real light source is always upright and appears behind the mirror, lateral inversion occurs.

SALT

SIze: Compared to the original object is it the same size smaller or bigger?
Attitude: Which way the image is oriented compared to the original object, upright, erect or inverted
Location: location of the image, in front or behind the mirror
Type: is the image a real image or virtual image

Plane Mirror Images

S: object size = image size
A: Always upright
L: Object distance from mirror = image distance from mirror
T: Always forms a virtual image and is reversed left to right = lateral inversion

Formulas needed to know

Frequency, period, magnification, wave equation, index of refraction, law of reflection, snell's law, critical angle, speed

Sclera

white part of the eye

Lens

the transparent structure behind the pupil that changes shape to help focus images on the retina

Cornea

The clear tissue that covers the front of the eye

Pupil

the adjustable opening in the center of the eye through which light enters

Iris

a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening

Retina

the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information

Cone cells

work best in bright light and enable you to see colors

Rod cells

work best in dim light and enable you to see black, white, and shades of gray

Optical Nerve

the nerve that carries neural impulses from the eye to the brain