Physics test investigation

Refraction

The bending of light as it passes through different densities of mediums

Refractive index

Value measuring how much a medium slows down the light passing through it

Higher refractive index=bends more=slows down more

Refraction in different densities

• When light moves into a denser medium (like from air to glass), it slows down and bends towards the normal line

• When light moves into a less dense medium (like from glass to air), it speeds up and bends away from the normal line

Total Internal Reflection

When light travelling from an optically dense material to a less optically dense substance hits the boundary at a certain angle it causes the light to just graze the surface and be reflected back into the surface

Conditions for TIR to happen

1. Light must travel from a denser to a less dense medium

2. The angle of incidence must be greater than the critical angle (the angle of incidence that produces an angle of refraction of 90 degrees)

Lens

Transparent plastic or glass that has at least one curved side and refracts light

Convex Lenses

• Thicker in the middle

• Converges light rays

• When parallel light rays travel directed at the convex lene from a perpendicular angle, they converge at a point called focal point

• Both real and virtual lenses, depending on the position

Concave lenses

• Thinner in the middle

• Diverge light rays

• When parallel light rays travel directly at the concave lens at a perpendicular angle, they diverge, making them look like they come from a point in front of the lens.

• This is a virtual focal point as light rays actually don’t pass through it

• Virtual, erect and reduced

Near sighted (myopia)

• Cause- The eyeball is too long or the cornea is too curved → the image focuses in front of the retina

• Symptoms- faraway objects look blurry

• Concave lenses or glasses expand the focal length OR laser surgery to change the shape of the cornea or lens

Far sighted (hyperopia)

• Causes- The eyeball is too short or the cornea is too flat → image is focused behind the retina

• Symptoms- Nearby objects look blurry

• Convex lens shortens the focal length OR laser surgery to change the shape of the cornea or lens

Astigmatism

• causes- Cornea is not perfectly spherical, resulting in distorted images as light rays are prevented from reaching a single point or focus

• symptoms- objects appear blurry at all distances

• Laser surgery, special astigmatism eyeglasses or contact lenses

Colour blindness

• Causes- Occurs when light sensitive cone photoreceptors in the retina fail to respond appropriately to variations of wavelengths of light that enable people to see an array of colours

• Symptoms- Usually hard to distinguish between shades of red and green

• No treatment

Focus

The specific point where light rays that were travelling parallel to each other meet (converge) after passing through a lens

Focal length

The distance between the center of the lense to the focus

Image formation- Convex- Virtual

• Distance is less than the focal length

↳ Virtual, upright, enlarged

Image formation- Convex- Real

• Distance is more than 2 focal length

↳ Diminished, inverted, real

Uses of convex lense

• Magnifying glass, Contact lenses for long-sightedness

Image formation- Concave

• Virtual

• Upright

• Diminished

Uses of Concave lenses

• Glass for near-sightedness (short-sightedness)

• Contact lense for near-sightedness (short-sightedness)

• Flashlight

Draw an eye and label

Aqueous Humour

Clear fluid that helps maintain eye shape and nourishes the cornea and lens

Cornea

Transparent front layer of the eye that protects the eye and bends (refracts) light as it enters.

Iris

Coloured part of the eye that controls the size of pupil

Lens (eye)

Transparent structure that changes shape to focus light onto the retina.

Retina

Light-sensitive layer containing photoreceptors (cones and rods) and converts light into nerve impulses

Sclera

Tough, white outer covering of the eye that protects it and helps maintain its shape.

Vitreous Humour

Clear, jelly like substance that fills the eye, maintains its shape, holds the retina in place and allows light to pass through to the retina

Pupil

Opening in the center of the iris through which light enters the eye.

Optic nerve

Carries nerve impulses from the retina to the brain

Ciliary bodies

Contain ciliary muscles that change the shape of the lens for focusing, and they produce the aqueous humour

Choroid

Layer containing blood vessels that supplies oxygen and nutrients to the retina. Also absorbs light

Step 1- Light entering our eyes

Light rays enter the eye through the cornea, a convex lens that focuses the light slightly by refracting.

Step 2- Light entering our eyes

Light travels through the pupil and the iris control the ring of muslces around the pupil which adjusts how much light enters

Step 3- Light entering our eyes

The light passes through the lens, which further focuses the light rays onto the retina

Step 4- Light entering our eyes

The retina is a layer of light sensitive cells- cones for colour and rods for brigthness

The rods and cones send electrical impulses to the brain along the optic nerve

Step 5- Light entering our eyes

The brain interprets the signals as visual images

Cone cells

• At the center of retina

• 3 types- Red, green, blue

• Detect colour of light

Rod cells

• At the edges of the retina

• Only black and white

• Detect brightness of light

The pupil- Contracting and relaxing

Dim light

• Iris muscles contract

• pupil dilates (open)

• Lets in more light

Bright light

• iris muscles relax

• Pupil constricts (close)

• Lets in less light

The lens- contracting and relaxing

Ciliary muscles

Distant objects

• Muscles relax

• Ligaments stretched

• Lens made thinner

Near objects

• Muscles contract

• Ligaments loosen

• Lens made thicker

How does the brain see

The optic nerve from the left eye connects to the right side and vice versa

So your brain sees everything reversed and switches them again