Subject: PHYSICS

Topic: Convex lens

Light refraction in Prism

Ray diagram of a convex lens

Ray diagram illustrating graphical construction rules of a convex lens

Simulation of the ray diagram

The six special case of convex lens

Daily applications of convex lens

Table of content

U se r ay diagr am t o illust r at e t he nat ur e of image

3 const r uct ion r ulesof r ay diagr am

D aily A pplicat ion

Convex lens(Conver ging lens)

L ight Ref r act ion in Pr isms(Revision)

Convex lens teaching flow chart

The light rays converge after passing through the prisms!!

In what way do the light rays pass throughthe prisms?

QUESTION TIME

Light rays passing through two prisms

QUESTION TIME

The light rays converge!!

AGAIN!!!The light rays also converge tothe same point!

QUESTION TIME

Will the light rays still converge if we continue

to cut the prisms?

NOYES NO

Convex Lens• thickest in the centre• bends light inwardsconverging lens

Which of the above is/are convex lens(es)?

A B C D

A & C

FF’ C

f

F: Focus F: Focus

Convex lens

C: Optical Center

f = focal length (FC)

Principal axis

Terminology of Convex lens

F: Focus

f = focal length (FC)

C: Optical Center

Principal axis

The light ray parallel to the principal axis The light ray through the Optical Center C The light ray through the focus F

F F C

is refracted parallel to the principal axis.

is refracted through the focus F.

passes straight through the lens.

Convex lens Construction Rules

Now, we are going to find the image of an object formed by a convex lens by using these rules.

ClassworkClasswork

By using the three construction rules of convex lens, draw a ray diagram of an object with object distance u = 15 cm. (Assume the focal length of the convex lens is 10 cm.)Can you find the imagedistance?

By using the three construction rules of convex lens, draw a ray diagram of an object with object distance u = 15 cm. (Assume the focal length of the convex lens is 10 cm.)Can you find the imagedistance?AnswerAnswer

Converging Lens Converging Lens SimulationSimulation

When the object distance is larger than 2f , do you know the image position?

Object

Image

2F 2F

QUESTION TIME

Case 1: Object distance >2f Case 1: Object distance >2f

Object

Image

• Magnified / Diminished / Same as the object

• Virtual / Real• Erect / Inverted• Virtual / Real• Magnified / Diminished / Same as the object

• Erect / Inverted

Between the position of F and 2F on the other side of the object.

• Position of image:

Descriptions of the image:Object distance >2f

Object

Image

2F

2F

QUESTION TIME

Case 2: Object distance = 2f Case 2: Object distance = 2f

Object

Image

• Magnified / Diminished / Same as the object

• Virtual / Real• Erect / Inverted• Erect / Inverted• Virtual / Real• Magnified / Diminished / Same as the object

Descriptions of the image:Object distance = 2f

At the position of 2F on the other side of the object.

• Position of image:

Object

Image

2F 2F

QUESTION TIME

Case 3: Object distance between f and 2f Case 3: Object distance between f and 2f

Object

Image

Descriptions of the image:Object distance between f

and 2f

Image distance > 2f on the other side of the object.

• Erect / Inverted• Erect / Inverted• Virtual / Real• Virtual / Real• Magnified / Diminished / Same as the object• Magnified / Diminished / Same as the object• Position of image:

Object

Where is the image?

2F 2F

Case 4: Object distance = f Case 4: Object distance = f

Object

Descriptions of the image:Object distance = f

• Position of image:

Image forms at infinity.

ObjectImage

2F 2F

QUESTION TIME

Case 5: Object distance < f Case 5: Object distance < f

ImageObject

Descriptions of the image:Object distance < f

On the same side of the object.

• Erect / Inverted• Erect / Inverted• Virtual / Real• Virtual / Real• Magnified / Diminished / Same as the object• Magnified / Diminished / Same as the object• Position of image:

Case 6: Very large object at infinityCase 6: Very large object at infinityFor a very large image at infinity:

Convex lens

The light rays are nearly parallel to each other!

F

F2F

2F

Do you know how parallellight rays are refracted?

Case 6: Very large object at infinityCase 6: Very large object at infinity Remember

the construction rules of convex lens.

Formed at the focal plane

• Erect / Inverted• Erect / Inverted• Virtual / Real• Virtual / Real• Magnified / Diminished / Same as the object• Position of image:

• Magnified / Diminished / Same as the object

Descriptions of the image:Object distance >2f

Formed at the focal plane

• Erect / Inverted• Erect / Inverted• Virtual / Real• Virtual / Real• Magnified / Diminished / Same as the object• Position of image:

• Magnified / Diminished / Same as the object

Descriptions of the image:Object distance >2f

Application of Convex lens

•Camera•Magnifying glass

The EndThe EndThe EndThe End