chapter 6.1 notes

3 things blind people can detect

1. A tiny part of the middle of a whole scene 2. The edges of their vision, but not directly ahead 3. Light and darkness

How does light enter the eye?

1. Light is refracted by the cornea 2.The refracted rays enter the pupil 3.The light rays pass through the lens and converge onto the retina 4.The Image formed is upside down, and cells in the retina change the image into electrical signals 5. Electrical signals are then sent to the brain along the optic nerve and then the brain changes the image upright

Night Blindness

A Condition in which it is difficult or impossible to see in dim light. Common cause is the rod cells losing their ability to respond to light.

Cataract

A cataract is a condition where the eye's lens has become cloudy this condition can naturally occur with age

Compound light microscope

A compound light microscope uses two convex lenses with relatively short focal lengths to magnify small objects

objective lens

A convex lens

snow blindness

A painful condition of temporary partial or complete blindness caused by overexposure to the glare of sunlight, such as on snow fields at high altitudes.

Telescope

A telescope uses a lens or a concave mirror that is much bigger to gather more of the light from distant objects

Optic nerve

A thick nerve that sends converted light rays called electrical signals made by the retina to the brain.

Cornea

A transparent tissue that covers the iris and pupil and is made of cells that are transparent enough to let light pass through, yet tough enough to hold the eye together. Also does most of the focusing in the eye.

Colour Blindness

Ability to only see shades of grey, and occurs in about one person in every 40000 .

Focussing

Adjusting the distance between the screen and the lens is called focussing.

Cone cells

Allow us to detect colours. We have three types of cone cells that each processes a different kind of pigment.If your brain receives an equal amount of all three colours, then we see the object as white. Our brain can combine and balance the different colour signals that it receives. This is why the white page of a book can appear white to us under varying amounts of daylight.

Image formed by telescope

Because it is brighter the image can be magnified to a greater extent to reveal more detail

lasers

Because lasers only contain one wavelength, the light does not refract into a rainbow , as would happen with normal light

Correcting Far-Sighted Vision

Can be corrected by a convex lens, so the light rays can converge directly at the retina.

When the screen is to close to the lens

If the screen is placed too close to the lens, then the light rays do not fully converge by the time they strike the screen .There will be an image formed but it will appear blurred.

Similarities in a refracting telescope and a microscope

In both the refracting telescope and microscope an objective lenses collects light and focusses it into an image. This image is formed inside the microscope and telescope and is never seen directly. Instead the image is magnified by the eyepiece lens, and directly into the eye of the operator or into a camera

Iris in bright light

In bright light, the iris contracts the pupil to reduce the amount of light entering the eye.

Iris in dim light

In dim light, the iris dilates or expands, the pupil to allow more light to enter

laser light

In laser light, all of the light has the same wavelength, all the light rays are moving in the same direction and all of the crests and troughs of the light are lined up

How to bring an image into focus

In order for the light rays passing through a lens to form a clear image, the screen that is receiving the image must be correct distance from the lens. The screen must be at the place where all light rays from a given point on the object converge.

fluid behind the lens

It gives shape to the eye and supports the lens

Colour vision deficiency

It is an inability to distinguish certain colours.

the fluid between the lens and the cornea

It supports both the cornea and the lens and provides nutrients to the cornea, which does not have any blood vessels

how does a digital camera work

It works by gathering and bending light with a convex lens.

Focussing system

Light first passes through the cornea where immediately the light is refracted towards the retina. Most of the focussing happens in the cornea. The lens does the remaining focussing.

Retina

Light rays pass the lens and focussed on a screen called the retina. This is where the image is formed.

Forming an image

Light rays that enter the eye from a spot at the top of an object come together at one place at the bottom of the retina. Light rays that enter the eye from one spot on the base of an object come together again in one place at the top of the retina. The image formed by the lens is inverted but your brain interprets the image as being upright.

Rod cells

Long cylindrical cells that can absorb almost any colour of light but they absorb green particularly well , but our brains do not use this to determine colour just shades of light and dark. This is called our black-and-white vision system, and in low-light conditions it helps us see shapes and movement.

sclera

Made of an opaque tissue that is white and surrounds the iris.

Optical fibre

Optical fibres are transparent glass fibres that can transmit light from one place to another

Far-sighted vision

People who can bring images that are distant into focus, but cannot bring close images into focus are far-sighted because light rays from nearby objects are diverging as they enter the eye.

Near-sighted vision

People who can see nearby objects clearly but cannot bring distant objects into focus are near-sighted because the lens converges at a point before the retina and by the time the light rays actually strike the retina they diverge and causes a fuzzy image.

Pupil

Pupil an opening that appears dark because light passes through it without reflecting back.

Treatment for snow blindness

Resting your eyes in a dark room for several days to allow the inflammation to decrease or wear goggles with thin slits to help prevent snow blindness.

What are the special cells in the retina that detect images

Special light sensitive cells

Telephoto lenses

Telephoto lenses have longer focal lengths. The image through a telephoto lens seems enlarged and closer than it actually is

Hubble space

Telescope type of reflecting telescope that uses two mirrors to collect and focus light to form an object, was launched in 1990

Far objet

The amount of light entering your eye decreases when the object is moved far away, and so the object appears to be dimmer

Blind spot

The area where the optic nerve enters the retina and does not have any light-sensing cells.

Shape of the eye changes

The change of shape can affect your ability to focus and may require the temporary use of eye glasses

What is involved in the focussing system

The cornea, the lens, and spaces in the eye filled with a watery fluid

diaphragm

The diaphragm is made of a number of opaque circles that are arranged in a circle. The circles can be moved to make the central hole larger or smaller. Light passes through the lens and forms an inverted image in both the camera and the eyes

eyepiece lens

The eyepiece lens which is a convex lens then magnifies the image again. this final image can be hundreds of times larger than the actual object, depending on the focal lengths of the 2 lenses .

What does the iris control

The iris controls the amount of light entering the eye

Iris

The iris is the coloured circle of muscle surrounding the pupil, its structure is what we refer to when we speak about the colour of someone's eyes being grey, brown, blue, or hazel.

lens

The lens has the ability to fine-tune or focus by automatically changing its shape

lenses

The lenses bend light to focus it, which is why a telescope

When the screen is too far away from the lens

The light rays converge and then they diverge before they strike the screen, resulting in a blurred image.

Objective lenses for refracting telescope

The objective lens in a telescope has a longer focal length than in a microscope because the objects are viewed from the lens

pixels

The pixels correspond to the rods and cones that detect light in our eyes

Astigmatism

The shape of the cornea is irregular and light rays can focus on more than one point on the retina making images look fuzzy.

Telescopes in binoculars

The telescopes in binoculars are shortened by placing prisms inside that serve as plane mirrors

The CCD has many tiny regions

These tiny regions are called pixels, each of which is capable of recording a tiny part of an image

What do lasers remove

They remove cataracts, re-attach retinas, stop bleeding, and reshape corneas

Magnify

To magnify means to cause to look larger than the real size

Binoculars

Two reflecting telescopes mounted side by side

Correcting Astigmatism

Use eye glasses, contact lenses or laser surgery to correct the shape of cornea.

reflecting telescopes

Uses a concave mirror, plane mirror, and a convex lens to collect and focus light from distant objects

What is a simple way to transport light

Using a optical fibre

Correcting Near-Sighted Vision

Vision Can be corrected by a concave lens so the light rays will diverge slightly so the image forms further back.

Blindness

Visual impairment that keeps people from doing things and most legally blind people can see some light and in rare conditions they can not see at all.

Normal Vision

When Light rays from a distant object enter the eye, the rays are nearly parallel. The lens causes the rays to converge at the retina, producing a sharp image. Light rays from a nearby object diverge when they enter the eye, so muscles in the eye cause the lens to change shape, making the lens thicker and gives the lens a greater ability to form a clear image.

Total internal reflection

When a light ray strikes the wall of the fibre it is reflected back into it

Thicker lens

When certain muscles in the eye contract, there is less tension on the lens, allowing the lens to be thicker. A thicker lens can focus on near objects

Thinner lens

When you look at distant objects, these same muscles relax, increasing tension on the lens and making it thinner

How can you change the shape of the cornea

You can change it by doing laser surgery

What are the special cells in the retina?

cone cells and rod cells

Malnutrition

lack of proper nutrition, caused by not having enough to eat, not eating enough of the right things.

How does light from a distant object enter through a reflecting telescope

light from a distant object enters from one side of the telescope and strike a concave mirror at the opposite side. The light reflects off the mirror and then converges. Before it converges at a focal point the light strikes a plane mirror that is placed at an angle within the telescope's tube. The light is then reflected from the plane mirror towards the telescopes eyepiece. The light rays converge at the focal point, creating an image of the distant object.

aperture

opening of a camera

charge-coupled device (ccd)

the detector at the back of the camera which absorbs light and provides the electrical signals needed to produce a digital image.

Energy from a laser beam

the energy is so intense that it can seal off blood vessels,which helps reduce bleeding during surgery

lens of a digital camera

the lens then projects an image onto a light detector to record a digital image of a scene

Wide-angle lenses

they must be placed close to the light detector to form a sharp image with their short focal length