Chapter 19
Astigmatism
A condition in which objects at any distance appear blurry because the cornea or lens is misshapen. It prevents light from focusing on the retina. It results in the lens having 2 different focal points, causing the image to be blurred or distorted. It can be corrected by specialized eyeglass lenses.
Virtual image
A copy of an object formed at the location from which the light rays appear to come.
Real image
A copy of an object formed at the point where light rays actually meet. Unlike a virtual image, this kind of image can be viewed on a surface such as a screen.
Plane mirror
A mirror with a flat surface. When you look into this kind of mirror, you see your reversed reflection- a right left reversed image of yourself. This kind of mirror always produces a virtual image. Ex. large mirror in the bathroom
Lens (part of the eye)
After passing through the pupil, light enters the convex (lens) in the eye. It's a sealed capsule containing a clear fluid. It focuses the light onto the light sensor cells at the back of the eye.
Pupil and iris
After the cornea, light rays pass through the (pupil), or the part of your eye that looks black. It's the opening that allows light rays to enter your eye. The colored part of your eye, (iris) contracts and expands to control the amount of light that enters your eye. The controlled movement of this is regulated by signals from the brain.
Telescope
An instrument that uses lenses or mirrors to collect and focus light from distant objects. In Greek, this word means "seeing from a distance". There are two main types of telescopes; reflecting and refracting.
Lens
An object made of transparent material that has one or two curved surfaces that can refract light. The curvature and thickness of this affect the way it refracts light.
Camera
An optical instrument that records an image of an object. Light rays enter this through an opening, are focused by the opening or lens, and form an image that is recorded on film or by a sensor.
Microscope
An optical instrument that uses lenses to provide enlarged images of very small, near objects. One common type of this is a compound (microscope). The compound (microscope) uses 2 convex lenses to magnify small objects.
Cornea
Light rays enter your eyes through the transparent outer coating of the eye (this). It's curved surface helps to focus light entering your eye.
What are some common vision problems?
Nearsightedness, farsightedness and astigmatism.
Ray diagram
Shows how rays change direction when they strike mirrors and pass through lenses.
Angle of reflection
The (angle) the (reflected) ray makes with the perpendicular line. It states that this is equal to the angle of incidence.
Angle of incidence
The (angle) the incoming (incident) ray makes with a line drawn perpendicular to the surface of the mirror. The mirror reflects the incident ray.
Critical angle
The angle of incidence that produces an angle of refraction of 90 degrees.
What happens when light enters a new medium at an angle?
The change in speed causes the light to bend, or refract.
Total internal reflection
The complete reflection of a light ray back into its original medium. Materials that have small critical angles are likely to cause most of the light entering them to have this happen to them.
What are the main parts of the eye?
The cornea, the pupil and the iris, the lens and the retina.
Retina
The focused, refracted light is collected here. It is the inner surface of the eye. It's surface is covered by light sensitive nerve endings called rods and cones. These convert the light into electrical signals that are sent to the brain through the optic nerve.
Focal point
The point at which the light rays meet.
Index of refraction
This for a material is the ratio of the speed of light in a vacuum to the speed of the light in the material.
Farsightedness
This is a condition that causes nearby objects to appear blurry. It's usually caused by having a cornea that is not curved enough or an eyeball that's too short, which cause the light rays that enter the eye to focus beyond the retina. It can be corrected by placing a converging, or convex, lens in front of the eye, which bends the light rays toward each other before they enter the eye.
Concave lens
This kind of lens is curved inward at the center and is thickest at the outside edges. These lenses always cause light rays to spread out and can only form virtual images.
Convex lens
This kind of lens is curved outward at the center and is thinnest at the outer edges. aka converging lenses. They can form both real and virtual images.
Refracting telescopes
This kind of telescope uses convex lenses to collect and focus light.
Reflecting telescopes
This kind of telescope uses mirrors and convex lenses to collect and focus light.
Nearsightedness
This occurs when the light rays that enter your eyes focus before they reach the retina. It causes distant objects to appear blurry. It happens because the cornea is too curved or the eye ball is too long. It can be corrected by pacing a diverging, or concave, lens in front of it, which spreads the rays out a little before they enter the eye.
Concave mirror
When the inside surface of a curved mirror is the reflecting surface, the mirror is classified as this. This kind of mirrors can form either real or virtual images.
Convex mirror
When the outside surface of a curved mirror is the reflecting surface, the mirror is classified as this. This kind of mirror always causes light rays to spread out and can only form virtual images.
