Unit C: Light and Optics

1.0

Properties of Light

• Light travels in straight lines

• Light can be reflected

• Light can be bent

• Light is a form of Energy

microscopes- magnify minute things

telescope- magnify things that are far away

Two Types of Telescopes

Reflecting telescope

Refracting telescope

Binoculars

two fixed refracting (bending) telescopes

Two types of reflection

Regular reflection- a smooth, flat surface

Diffuse- rough, jagged surface

The Law of Reflection

The Law of Reflection states that the angle of incidence is equal to the angle of reflection

Curved Mirrors

Concave mirrors- form an image that appears closer than it is and can be useful because it directs light everywhere. The focal point is in front of the mirror. ex. headlights, flashlights

Convex mirror- forms images that appear much smaller and farther away. They can reflect light from a large area. ex passenger side mirror

Refraction- the process in which light is bent as it transfers from one medium to another. Different media can alter the speed at which the light travels, causing it to bend

The Law of Refraction

The Law of Refraction states that when light travels from a less dense medium to a tender medium, it bends toward the normal. Similarly, when light travels from a more dense medium to a less dense medium, it bends away from the normal.

Mirage- is caused by refraction when light interacts with air with different temperature layers. Hotter air is less dense than cooler air

Lens- a curved piece of glass or transparent material

Image formation in a double convex lens

Three scenarios are possible based on where you place the object.

Beyond 2F (2 focal lengths away)- the image projected is real, reduced, and inverted

Between 2F and 1F- the image projected is real, inverted, and enlarged

Between the lens and F- this is diagram B. The image is not real (virtual,) is upright, and enlarged

The Wave Model of Light

Light behaves as a wave

Rest position- when a wave passes through the line that represents time, it is called a rest position

Crest- top of the wave

Trough- bottom of the wave

wavelength- the distance from crest to crest and trough to trough

Frequency

• is the rate at which troughs and crests move up and down

• frequency is measured in cycles per second

• a cycle per second is a hertz (Hz)

The Electromagnetic Spectrum

• EMR- electromagnetic radiation

• and electrical field induces a magnetic field and that is how that wave continues

• the longer the wavelength is, the slower the frequency and the lower the energy is

• the shorter the wavelength is, the faster the frequency and the higher the energy is

Radiowaves

• use for communication

• searching for extraterrestrials

• bounces off objects

• used for communication

• MRI (medical resonance imaging)

Microwaves

• used for cooking- it excites the water particles, causing steam and cooking

• RADAR- radio detection and ranging)

Infrared

• cant be seen but is felt as heat

• thermograms

Visible Light- ROY G BIV

UltraViolet (called ultraviolet because it comes after violet)

• sunburns

• retinal damage

• skin cancer

X-rays

• used in medical imaging

• mutations

• can’t pass through lead

Gamma Rays

• cosmic radiation

• the ozone layer blocks the rays

• super high in energy

• small

• used for blasting cancer cells (radiation therapy)

Light energy

• electrical

• mechanical (kinetic)

• chemical

• thermal

Sources of Light

Natural

• sun

• candles, oil, wood (burning)

• bioluminescence ( firefly, angler fish, plankton)

Artificial

• incandescent (old-fashioned light bulbs, filament)

  Fluorescent (paint, tube- uses phosphor powder)

Phosphorescent

• glow in the dark (triggered by light)

Chemiluminescent

• glowstick

• triggered by chemical reactions

The Primary colors of light

Theory of Colour Addition

The theory of color addition states that if you mix all three colors, you get white

The Eye

How the Human eye is compared to a Camera

• pupil- aperture

• iris- diaphragm

• retina- film

• lens-lens

How the Eye Works\

• light enters the eye going through the cornea

• the iris constricts or opens to control the amount of light

• the ciliary muscles change the shape of the lens to help focus the light (this is called an accommodation reflex)

• light is then focused on the retina

• photoreceptors are stimulated by the light and send a chemical electrical signal, via the optic nerve

• Photoreceptors are cells that detect light

• Rods- light intensity

• Cones- color

• the brain interprets this signal as an image

Eyesight Difficulties

• Astigmatism is caused by an irregularly shaped eyeball

• If your eye is too long, images form in front of the retina. This is called near-sightedness or myopic vision. Myopic individuals can see up close unaided.

• If your eye is too short, the image forms behind the retina. This is called far-sightedness or Hyperopic vision. Individuals with hyperopia can see far away unaided

  

• Near-sightedness is corrected with a concave lens

• Far-sightedness is corrected with a convex lens

• Laser eye surgery uses lasers to change the shape of the cornea

Eyes in the Animal Kingdom

• Humans have what are known as “camera eyes” a retina, a cornea, and a lens

• most vertebrates have camera eyes

• Fish have perfectly round eyes therefore, they can see in almost all directions

• nocturnal animals have a tapetum lucidium, a layer which acts as a mirror

Compound Eyes

• Insects and crustaceans have compound eyes

• each individual eyes are made up of smaller units called ommatidia (pl.) or a singular ommatidium that are great for tracking movement

• but are lousy at forming coherent, or full, images

• a mosaic image is formed

Stadium Images

• are formed when cards are held up like an individual pixel

  

• pixels (picture elements) are small units of color used in digital imagery

• the greater the amount of pixels, the higher the resolution

• resolution refers to the pixel density

THE END