optics

What is light?

• Light is energy and travels like a wave

• Small packet of light energy is called a photon

• Electromagnetic radiation

• Electromagnetic waves are made up of electrical energy and magnetic energy and does not require a medium

Types of electromagnetic waves:

Radio 10³, Microwave10-², Infrared-⁵, Visible10-⁶, Ultraviolet10-⁸, X-Ray 10-¹⁰, Gamma Ray 10-¹²

Crests:

Waves have a highpoint

Troughs:

Waves have a low point

Wavelength:

The distance from one crest (or trough) to the next crest (trough)

Amplitude:

The distance from the centre line to crest or trough

Electromagnetic Spectrum:

• Graph that shows the various types of electromagnetic radiation

• Arranged by wavelength and frequency

Frequency:

The number of peaks that pass a point in a certain time span

Also cycles per second measured in hertz

High Energy:

High Frequency and short wavelength

The longest waves are the radio waves and the shortest are gamma waves

All waves shorter than visible light:

Can cause cancer

• UV - light - sun burn and skin cancer

• X-rays can cause cancer (that is why the dentist leaves the room when she X-rays your teeth)

Gamma rays are:

The most dangerous

• They kill ALL living things and cause cancer

• BUT also used to treat cancer because they destroy cancer cells

Incandescent:

An object, as it gets hotter will eventually produce light.

Production of light as a result of high temperatures

Ex. Fiament of a burner and a stove set to a high temperature

Light from Electric Discharge:

Electricity causes gas to glow

Process of producing light by passing an electric current through a gas

Ex. Flash of lightnings, neon lit-up sign

Phosphorescent:

The process phosphorescent is done by phosphor absorbing light energy which is mostly ultraviolet light. It keeps some energy and releases visible light of lower energy. Hold onto energy for (1 day - months)

Often described as glow in the dark like glow in the dark stars

Fluorescence:

When an object absorbs ultraviolet light and immediately releases energy as visible light and absorbs UV.

Ex. Detergent manufacturers use this to make clothes appear brighter

Chemiluminescence:

Result of a chemical reaction without heat and the reactions creates unstable light

Ex. Glow in the dark sticks

Bioluminescence:

When chemiluminescence happens in living organisms it creates it. Created through chemical reaction.

Triboluminescence:

The production of light when certain crystals are scratched crushed or rubbed.

Ex. When sugar will sparkle when broken or scraped in the dark

Light - Emitting Diode (LED)

Electronic device that allows an electronic current to flow in only one direction

Ex. Christmas Lights

Light can be…

1. Reflected

2. Absorbed

3. Transmitted

Reflected:

Light bounces off a surface and changes direction

Absorbed:

Light is absorbed and the energy is converted to heat

Transmitted:

Light passes through the object

Light can be transmitted:

1. Transparent

2. Translucent

3. Opaque

Transparent:

Substances transmitted light fully without any change in direction

Ex. Clear Glass

Translucent:

Substance pass light but it is scattered on different directions.

Ex. Waxed Paper

Opaque:

Substance do not allow light to pass and all light is reflected or absorbed

Ex. Wood

Light can be refracted:

• Light rays appear to “bend” when traveling from one medium to another

Light can be diffracted:

• Diffraction is the apparent bending of waves around small obstacles and the spreading out of the waves past small opening

The path of light and shadows:

• A light ray diagram shows what happens to light as it travels through some substances and reflects off others

Shadows:

• A shadow is a dark region that forms behind an object that is illuminated

• Shadows are formed when absorbed or reflectwd of the light falling on an object is translucent or opaque

• Only translucent and opaque objects produce shadow

  Ex. At night we are in the Earth’s shadow

Umbra:

Darkest shadow no light

Penumbra:

Edges of the dark shadow

Regular reflection:

Occurs when light is reflected off a smooth surface

• Because light travels in straight lines, the angle that the light strikes the surface at (the angle of incidence) is the same as the angle that the light leaves the surface (the angle of reflection)

Incident Light Ray:

Light emitted from a source that strikes an object

Reflected Light Ray:

Light which is reflected/bounced off the mirror

Normal:

Imaginary line drawn at 90° from the mirror surface

Mirror:

Any polished surface reflecting an image

Reflection:

The bouncing back of a light from a surface

What is Visible Light?

Can be defined as a form of electromagnetic radiation that is visible to the naked eye

Properties of Light:

• Travels fast (3.0 × 10⁸ m/s in vacuum)

• Travels in a straight line (path is a called a ray)

• Can travel through a vacuum (empty space) doesn't need material to carry it, pure energy

• Reflects off surfaces and bends when it changes mediums

How is light produced?

All sources of lights have atoms that absorb some form of energy, making them “excited”. Atoms can release energy in the form of light

• Shake an electronic and you get an electromagnetic wave

Luminous:

Produce it’s own light (e.g. Sun, lamp)

Non-luminous:

Means it does not produce its own light (e.g. Moon, cookies)

The law of Reflection:

The angle if incidence is equal to the angle of reflection

Types of Reflections:

• Clear

• Diffuse

Clear (Specular):

Reflection of light off a smooth surface

Diffuse:

Reflection of light off an irregular surface

Total Internal Reflection:

• When light travels between mediums, some light is reflected and some is refracted

• Light bends away from the normal when it speeds up at the boundaries of two mediums

• ANGLE OF REFRACTION IS LARGER THAN THE ANGLE OF INCIDENCE

Critical Angle:

• The angle of refraction continues to increase as the angle of incidence increases

• Eventually, the angle of refraction will become 90°

• At this point the angle of incidence is called this

It trapped

If the angle of incidence increases past the critical angle, the refracted ray will not exit the medium

• It will reflect back into the medium

• called TIR

Lens:

Transparent objects with at least one curved side that causes light to refract

The Thin Lens Equation

Describes the relationship between:

F - focal length of lens

d o - distance of the object (from lens)

d i - distance of image

The equation:

I/F = I/do + I/di

I/di = I/F + I/do

I/do = I/F + I/di

In convex lenses:

• F is positive

• do is ALWAYS positive

• di is positive if the image is real negative means VIRTUAL

Magnification Equation:

M = hi / ho = - di / do

Image height - hi

Object height - ho

If M>1, image is larger than object (enlarged)

If M<1, image is smaller than object (reduced)

Refraction:

The bending of light as it passes from one medium into another

• Ex. Air into water

The speed of light:

• Light travels at almost 300 million m/s when there are very few particles

• Ex. In a vacuum

The Index of Refraction:

• The amount by which a transparent medium decreases the speed of light

• The larger thr refractive index, the more the medium decreases the speed of light

n =

The refractive index of a medium

v =

The speed of a light in the medium

c =

The speed of light in a vacuum

Index of refraction of material:

n = c/v

= speed of light in a vacuum / speed of light in medium

How Light Refracts:

• As light compression enter a medium with a higher refractive index they compress (slow down)

• When goes from dense then not dense it bends away from the normal (vice versa)