Lenses

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Lenses

K Warne


Refraction of waves• Waves slow down

on entering a more dense medium.

• If the wave strikes this medium at an angle it then changes direction.

Normal line 90° to the surface

The wave bends towards the normal on entering a more dense medium at an angle.

The waves bend away from the normal when exiting a more dense medium.


Refraction• Waves

bend towards the normal when entering a more dense medium.

Incident ray

Refracted ray


Converging Lenses


Diverging Lenses


Ray Diagrams - Optical Centre

Principle axis

In a thin lens the displacement is negligible. The rays are drawn as if refracting from the center line.

.F


Ray Diagrams - Optical Centre

Principle axis

Light rays passing along the principle axis are not refracted as they strike both surfaces at 90°

Any ray passing through the Optical centre can be thought of as passing straight through.

In a thin lens the displacement is negligible.


Ray Diagrams -Focal Point

…………………….

… ....

F ……... ………..

•

Any ray striking the lens ………… to the principle axis is refracted through the …………….. point.

These values are the ………… for either side of a ………...………… lens.

Parallel to ………………… ………..

…………….…….

•••


Diverging Lenses

F

F -……. ……….

……. …………..•

In a diverging lens the rays …………………. to have originated at the ……………… point.


Convex lens Images

Object on one side an image is formed on the ……….. side. Image properties:

• ………… (can be cast on a ………..) (type)

• ...................................………… (position)

• ……….. than the object (…………………) (size)

• and ……………………... (orientation)

Object

………….

…… …….

…..

…2F F F 2F••• ••

Magnification or Di

screen


Diverging Lenses


Light PracticalGroup 1 - Part I

Measure the angle of incidence when the angle of refraction is 90°

Part II GROUP 2-5 - Part 2

• Optical bench - measure the distance from the object to the lens, height of the object and the distance from the image to the lens and the height of the image.

Do Ho Di Hi

1

2

3

4

GROUP 6 & 7 Diagrams (Ray Diagrams)


Convex lenses Do=2F

Object placed at 2F the image is:

• Real

• At 2F

• Same size as object

• inverted

Ho

Object

Image

Do Di

HiF= 50cm

2F F F 2F


Ray Diagrams -Object closer than the Focal length

Image -

• ………………………

• ……………………

• ……………………..

• ………………………..

F F••

An object placed between F and the lens.

The lens would now be functioning as a ……………………………..


Light Practical

Object Image

Do Di

Ho Hi

Do greater than 2F

Do equal to 2F

Do less than 2F

F= 50cm

Ray diagrams p 39

2F


From World Book © 2002 World Book, Inc., 233 N. Michigan Avenue, Suite 2000, Chicago, IL 60601. All rights reserved. World Book illustrations by Charles Wellek

From World Book © 2002 World Book, Inc., 233 N. Michigan Avenue, Suite 2000, Chicago, IL 60601. All rights reserved. Nikon, Inc.

Eye vs CameraEye vs CameraPupilIrisRetinaLens

Discuss the nature of the image formed in terms of size, position, orientation and type.

Also discuss how focusing and controlling the amount of light entering is achieved in both.

LensAppetureFilm


Eye - DefectsEye - Defects

This is commonly called short sighted.

Distant object brought ‘closer’

Distant objects the lens is not stretched enough. (Too fat)

Rays are focused in front of retina.

Object close up are focused clearly.

A diverging lens would cause distant rays to focus on the retina and normal sight is restored.

Short Sighted


Compound Microscope

F•

2F

F F 2F

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Keith Warne

Lenses

Education

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