Refraction and Lenses

Dispersion of refracted sunlight by a water drop produces

the rainbow

In a vacuum, different colors of light travel at

the same speed

Concave Lenses are

thinner at center than at the edges, the lens is curved inward at the center

The image point of the top of the object is the point where the

three refracted rays intersect. Since the three refracted rays are diverging, they must be extended behind the lens in order to intersect. All three extensions should intersect at the same location. The point of intersection is the image point of the top of the object.

To locate the position of the image, you only have to know the paths of

two rays from a point on the object. Choose a point at the tip of the arrow representing your object

Telescopes

use a collection of lenses to collect and focus light from very distant objects, uses a lens that forms a real image of a distant object

Microscopes

uses combination of lenses to enlarge or magnify an image that is near

Cameras

uses lenses to focus light and record image of an object, instrument that work most like a human eye, consists of a convex lens

Compound Microscope

uses two converging lenses (convex lenses) of short focal length. The objective lens produces a real image of a close object. The image is farther from the lens than the object so it is enlarged. The eyepiece forms a virtual image of the first image, further enlarged

Positive Diopter

value means Convex (converging) lens is used to correct Farsightedness, image produced with glasses will be in front of image seen without glasses. Focal length is positive.

Negative Diopter

value means the lens is a Concave (diverging ) lens used to correct Nearsightedness, image produced with glasses will be behind image seen without glasses. Focal length is negative

Because light rays never meet, concave lens only produce

virtual images

The image formed by a diverging, concave lens is always

virtual, right-side up, reduced, and cannot be projected on a screen.

At a certain angle, the beam no longer emerges into the air, but skims along the surface of the

water

The focal length of a lens

whether converging or diverging, is the distance between the center of the lens and its focal point

Nearsighted

(eyeball is too long)---can see close up, but objects at a distance are blurry.

Farsighted

(eyeball too short)—can see at a distance, but nearby objects are blurry. Here the eye focuses light behind the retina because the eyeball is too short

The Law of Refraction, called

Snell's Law

Index of refraction (n) =

Speed of light in vacuum/Speed of light in material

Refraction

The bending of light as it is transmitted through transparent material, the bending of a wave as it crosses the boundary between two media at an angle

Image distance

The distance from the center of the lens to the image. An image can be real(inverted and be able to be projected on a screen), or virtual

Object distance

The distance from the center of the lens to the object

There is also a spot in the retina where the nerves carrying all the information leave the eye in a narrow bundle.This is the

blind spot

Convex lens are also called converging lens because they

bring light rays together

The change in speed of each color affects the amount the light bends (refracts). It depends on upon the

color of light and it's frequency

In a nearsighted person the eye focuses light in front of the retina because the eyeball is too long. Need

concave lenses in glasses to see more clearly because it will spread out the rays (diverge) before entering your eyes, causing the image to form further back in the eyeball, on the retina.

The focal point is the point at which a beam of light

converges on that principal axis

A magnifying glass is simply a

converging lens (convex lens) that increases the angle of view and allows magnification to occur.

Farsightedness can be corrected by the use of a

converging lens. Light refracts before reaching the cornea and is subsequently focused on the retina of the eye

farsighted need glasses with

convex lenses, It makes the rays bend toward each other (converge), before entering your eye causing the image to form on the retina so you can see clearly

It helps focus light and also helps to protect the eye. Light enters through the transparent, protective covering, the

cornea

Lenses are used to change the path of light rays before they enter your eyes in order to

correct or help your vision

The SI unit for the power of eyeglasses is the

diopter, which equals the reciprocal of a meter

The separation of white light into colors arranged according to their frequency is called

dispersion

Concave lens are a type of

diverging lens, because the Lens cause the light rays to spread out

Nearsightedness can be corrected for by the use of

diverging lens, light diverges before reaching the cornea and is then converged to a location on the retina

A diverging lens is often used

for the viewfinder on a camera

Ray diagrams are used to

graphically analyze how light rays behave when they pass through a lens and predict where the image formed will appear

A bulging cornea or an elongated eyeball often increase the refracting power of the eye, leading to the formation of images

in front of the retina

The ratio of the speed of light in a vacuum to the speed of light in a given material is called the _________ of that material.

index of refraction

The brilliance of diamonds is a result of total

internal reflection

The image is located where the three rays intersect. Head of arrow placed at

intersection

The amount of light that enters is regulated by the __________ the colored part of the eye that surrounds the pupil

iris

Astigmatism may accompany nearsightedness or farsightedness. Usually it is caused by an

irregularly shaped cornea, but can also occur with an irregularly shaped lens

Internal Reflection

is a consequence of the refraction of light.

pupil

is the opening through which light passes. The pupil becomes smaller in bright light and larger in darkness (to let more light in)

The focal point

is the point at which a beam of light, converges on that principal axis

A convex lens is similar to the concave mirror and can also cause

magnification

If the object is placed between the focal point and the lens, the lens can

magnify the object

No net bending occurs in the

middle (at optical or principal axis) and the rays of light emerge in their original direction

Snell's Law Formula

n1 sin𝚹1 = n2 sin𝚹2 - Where n1 and n2 are the index of refraction of the media on either side of the boundary, and 𝜽1 and ϴ2 are the angle of incidence and angle of refraction.

The di will be a positive number because on opposite side (right side) of the lens, but the hi will be

negative because real image is inverted

Past the critical angle, there is total internal reflection

no refraction

Focal point would appear to be on the left side of lens since the rays spread out on other side, but a true forming of a focal point is

not seen

Magnification

occurs when the use of a lens allows an image to be observed through a wider angle than would be observed without the lens

Astigmatism

of the eye is a defect that results when the cornea is curved more in one direction than the other. Because of this defect, the eye does not form sharp images.

Method for Drawing Ray Diagrams of Convex Lens

1. A ray parallel to the principal axis will be refracted by the lens to the focal point. 2. A ray will pass through the center with no appreciable change in direction. 3. A ray that passes through the focal point in front of the lens emerges from the lens parallel to the principal axis.

BECAUSE OF REFRACTION, OBJECTS SEEM TO APPEAR

AT A DIFFERENT PLACE FROM WHERE THEY REALLY ARE

Drawing ray diagrams of diverging lenses

1. Pick a point on the top of the object and draw three incident rays traveling towards the lens. 2. Once these incident rays strike the lens, refract them according to the three rules of refraction for double concave lenses.

thin-lens equation

1/f = 1/do + 1/di

Power =

1/focal length

The distance from this focal point to the center of the lens is called the

Focal length

critical angle

It is the angle at which the light is refracted at an angle of 90° with respect to the normal

If the object is at the focal point, the rays do not converge, they never intersect (forward or back) and therefore

NO image is formed

Convex Lenses

Refracts parallel rays of light so that they meet at a True Focal Point. They are bent toward the center of the lens.

You can calculate the critical angle or minimum index of refraction that will produce total reflection of a ray by using the formula:

Sinϴc = n1/n2

Focal point

The point where parallel rays of light meet ( or appear to meet) after passing through a lens.

Snell's Law

is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different media, such as water and glass. It describes how light bends when traveling from one medium to the next

Focal plane

is a plane perpendicular to the principal axis that passes through the focal point of a lens

The image is focused on the retina by changing the thickness and shape of the lens to regulate its focal length. This is called

accommodation and is brought about by the action of the ciliary muscle, which surrounds the lens

A diverging lens

also known as a concave lens, is thinner in the middle and thicker at the edges, causing the rays of light to appear to originate from a single point, but the refracted rays do not form a true focal point

A converging lens

also known as a convex lens, is thicker in the middle and thinner at the edges, causing rays of light that are initially parallel to meet at a single point, the focal point

When a diverging lens is used alone, the image is

always virtual, (+hi), right-side up, and smaller than the object and on the same side of the lens as the object (-di) It makes no difference how far or how near the object is

Total internal reflection occurs when the

angle of incidence is larger than the critical angle and light is going from a slower moving medium to a faster moving medium

Real lenses

are not made of many prisms, but of solid pieces of glass or plastic, transparent material with surfaces that are usually ground to a spherical shape, which refracts light to form an image

The real image is projected in space to be examined by another lens, called the eyepiece, used

as a magnifying glass,

When you use a magnifying glass, you hold it close to the object you wish to see magnified. When you use a magnifying glass, you hold it close to the object you wish to see magnified

be negative, because on left side of lens

The inability of the lens to assume a short focal length leads to the formation of an image located

behind the retina

Different parts of the retina receive light from different directions. The image is then sent to the brain along the ___________ in order to interpret the image and turn the image right-side up

optic nerve

The principal axis

or optical axis of a lens is a line passing through the center of the lens perpendicular to the lens surface

The most net bending of rays occurs at the

outermost edges, for they have the greatest angle

In the human eye, most of the focusing is done by the cornea, the transparent membrane at the

outside of the eye

Binoculars

pair of identical telescopes mounted side by side, Each side of a pair of binoculars uses a pair of prisms that flips the image right-side up

The emerging beam of light will bend (refract) as it emerges from the water into the air as it

picks up speed and bend away from the normal

But when the object is NOT on the focal point, light converges and

produces an image

These converging lenses are used for

projecting images on walls or screens

The size and location of the object, image distance from the center of the lens, and the focal length are used to construct the

ray diagram

Image formed depends on position of the object in relation to the focal point. Convex lens form either

real, inverted images or virtual upright images

When the object is beyond the focal point of a converging lens (convex), the image formed is a

real, upside down image

To calculate the power of a pair of prescription glasses you take the

reciprocal of the focal length. The focal length is measured in meters

A rainbow is an illustration of dispersion due to

refraction

A distorted image, called a mirage, is caused by

refraction of light in Earth's atmosphere.

A lens is a piece of glass or plastic that

refracts light

An arrow is used to

represent the object,is placed on the axis

Light passes through the pupil and through the converging lens (convex) and is focused on a layer of light-sensitive tissue at the back of the eye—the

retina

Ray diagrams

show the principal rays that can be used to determine the size and location of an image

A lens forms an image by bending parallel rays of light that pass through it. All lenses rely on light having a

slower speed in the lens; going from gas (air) to solid (lens)

Optical fibers

sometimes called light pipes, are transparent fibers that transport light from one place to another

Light travels faster through hot air than through

the cooler air above

The focal length of a diverging lens is always a negative number (left side of lens) because

the other side the light is diverging. The di is a negative number too because on left side of lens