Erta Tema Optics
Optics is a branch of physics that studies the behaviour and properties of light, as well as mirrors, lenses, and how we humans/ our eyes perceive light.

If any form of electromagnetic is on the left side; warm colours mostly (longer wavelengths) green-to red then they have low frequency and less energy

If the form is on the right side/shorter wavelengths (green-violet), they have high frequency and high energy.

3 Possibilities

Light is transmitted

Light is absorbed (opaque)

Light is reflected "bouced back" (transparent).
It can also be described as the law of Reflection
(talked more in "Looking into mirrors and forming
images"

What is light?

Visible light is a form of energy that can be detected by the human eye.

When we see objects, we are actually seeing light being reflected

Properties of Light

The behavior of light:
Light travels in straight lines and
when emitted from a source to strike
an object, it creates an incident light

The law of Reflection
states....

1. When light bounces off a plane (flat) mirror,
the angle of incidence = the angle of reflection

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

The "Normal" is the perpendicular line to a
mirror surface

Drawing Ray Diagrams

Ray diagrams help is predict how light will
behave and how images are formed

The Dashed line (in Green)is drawn when the
ray is behind the mirror to show that the light
ray isn't really there but what we see into the mirror/imaginary

Solid lines (in Red) is drawn for a light ray
that is reflected from the mirror and into
the eye of the viewer

Steps to follow when drawing a Ray Diagram

1) Draw at least two incident rays (from each point on the object)

2) Draw at least two incident rays (from each point on the object) and draw the reflected ray directly towards the mirror at 90 degrees

3) Draw Another incident ray striking the mirror (at an angle) At that point it hits the mirror, draw a normal

4) Measure the angle of incidence with a protractor. Apply the law of reflection and draw the reflect ray

5) Using dashed lines, extend both reflected rays behind the mirror until they meet. Label this point

6) Repeat for each point on the object. Connect the points of the image using a dashed line

An image of a ray diagram with all the steps listed above

Characteristics of Images formed
S.A.L.T

S:Size
Is the image larger, same, or smaller

A: Altitude
Is the image upright or inverted (upside down)

L:Location
Is the image in front of the mirror? Behind the mirror?

T: Type
Is the image real or virtual

Curved Mirrors

Center of Curvature "C"
The centre of the sphere whose surface has
been used to make the mirror and
all "Normals" meet at C

Principle Axis "PA"
The line that passes through the centre of
curvature (C) to the midpoint of the mirror

Vertex "V"
The point where the principal axis meets the
mirror

Focal Point "F"
Halfway point between C and V

Distance between C and V is the radius

Focal Length "f"
Distance between F and V

Characteristics

- Can produce real and virtual images, image can enlarged, smaller, or the same size

Rules/steps for Concave mirrors

1) 1st incident ray parallel to the PA is reflected through the F

2) A ray passing through the C is reflected back onto itself

3) 2nd incident ray passing through
the F is reflected, parallel to the PA

4) A ray aimed at the V obeys the laws of reflection (<i = <r)

5) Where two reflected rays intersect
is where the image will form

Cases for Concave Mirrors

Concave mirrors in our Everyday lives

Characteristics

Image is virtual

gets smaller in size than the object, but as the object approaches the mirror, it grows larger (maximum up to the size of the object).

Rules/steps

1) A parallel ray that extends from the top of the object to the mirror and is reflected back to the viewer (virtual extension to focal point behind the mirror) - Red Line on image below

2) A ray aimed at C is reflected back upon itself
- Blue line on image below

3) A ray aimed at F is reflected parallel to the principal axis
Green line on image below

Case

Examples of Convex Mirrors in our Everyday lives

What is refraction

Refraction is the bending of light or change in direction of light as it travels from one medium to another

Key Ideas/Terminology

Light travels at speed of 3x10^8 m/s (in a vaccum)

-Travelling between mediums changes speed and direction of light

Vacuum- any particular space that technically has no matter. ***So insignificant that is doesn't affect the speed of life

Boundary: The surface between 2 mediums (ex. air and glass)

Incident Ray: Incoming ray that strikes the boundary

Angle of Incidence: The angle between the NORMAL and an INCIDENT RAY (<i)

Reflected Ray; The ray that is bent upon entering a second medium

Angle of Reflection: The angle between the NORMAL and REFRACTED RAY (<R)

***NOTE :
Angle of Refraction - Capital R - <R
Angle of Reflection - Lowercase r - <r

Angle of incidence does not equal angle of Refraction

Index of Refraction "n"

The index of refraction is the measure of the bending of a ray of light when passing from one medium into another.

Examples

Air has a index of refraction of 1.0003

Partial and Total Internal Reflection

Partial Reflection and Refraction occurs when a wave is travelling between two mediums. Some of the wave is reflected back and the rest is refracted through into the other medium.

Total Internal Reflection is a phenomenon where the incident ray is entirely reflected back from the boundary (no refraction occurs)

Key Ideas of Total Internal Reflection
-Only occurs when light travels from slow to fast medium
-Occurs when angle of incidence is greater than the critical angle

The Critical Angle is the angle of incidence that
results in an angle of refraction of 90°

Snell's Law

Formula

ni (sin˚i) = nR (sin˚R)
or
n1 (sin˚1) = n2 (sin˚2)

ni=index of refraction for medium 1
nR= index of refraction for medium 2

Examples of word problems

What are lenses

Lenses are transparent objects causing light to refract

Key Ideas/Terminology of Converging vs Diverging Lens

Curved Surface of a lens causes rays to pass through the top and bottom of the lens to be refracted more than rays that pass through the middle of the lens

Terminology

Principal Axis "PA":
A line that passes through the center of the lens normal to the lens surfaces

Optical Center:
The exact center of the lens "O"

F and F' are equal to length in 'O"

Principal Focus "F"

Converging lens: opposite side of the lens as incident ray

Diverging Lens: Same side of the lens as the incident ray

F-Primary principal focus

F' - Secondary Principal Focus

Images formed by each type of lens

Converging Lens

Rules/Steps

1) A ray parallel to the principal axis is refracted through the principal focus (F)

2) A ray through the secondary principal focus (F') is refracted parallel to the principal axis

3) A ray through the optical center (O) passes straight through without being refracted

Diverging Lens

Rules/Steps

1) A ray parallel to the principal axis is refracted as if it had come through the principal focus (F)

2) A ray that appears to pass through the secondary principal focus (F) is refracted parallel to the principal axis

3) A ray through the optical center (0) passes straight through without being refracted

NOTE: 2F and 2F' are always TWICE the distance of f and f' respectively

Cases

Thin Lens Equation and Magnification Equation

Thin Lens Equation

Magnification Equation

Summary of
+/-
Sign Convention

Examples of questions and answers

Understanding the Eye

Structure

Retina

Pupil

Iris

Cornea

Optic Nerve

Lens

A camera has a DIAPHRAGM that controls the amount of light entering it. The coloured part of the eye, also known as the “IRIS” has this function as it opens and closes around a central hole to let in more or less light.

The PUPIL compares to the APERTURE on a camera. This the opening in the iris through which light reaches the eye.

A camera has a CONVERGING LENS to refract light to form a sharp image. The eye also has structures, the LENS and CORNEA, that cause light to converge. The cornea is the transparent bulge on top of the pupil that focuses light. Light is refracted more through the cornea than through the lens.

In a camera, the image is focused on FILM or on a DIGITAL SENSOR.  The RETINA at the back of each eye cavity performs the same function as light-sensitive cells. The retina transforms light into an electrical signal that the optic nerve sends to the brain.

FOCUSING PROBLEMS

Hyperopia (far Sightdness)

When an individual has difficulty seeing nearby objects

Distance between the retina and the eye shape is too small and/or cornea lens combination is too weak

Causes light from all nearby objects to focus behind the retina

How do people correct this vision? What lens is used?

A converging lens is used to correct farsightedness by compensating for the eye's under convergence. The converging lens creates an image that is farther away from the eye than the object, allowing the farsighted individual to clearly see it.

Myopia (Near-sightdness)

When an individual has difficulty seeing objects that are far away

Distance between retina and lens is too large or the cornea-lens combination converges light to strongly

Light is brought to a focus in front of the retina

How do people correct this vision? What lens is used?

Nearsightedness is treated with a diverging lens, which makes up for the eye's over-convergence. The diverging lens produces the image closer to the eye than the object, allowing the nearsighted individual to clearly see it.