LENS EQUATIONS

LENS EQUATIONS

Magnification

Focal length

Height of image

Height of object

distance from the image to the optical centre

distance from the object to the optical centre

Definition

Inverted imageUpright imageM

Diverging lensConverging lensf

When measured downward

When measured upward

hi

When measured downward

When measured upward

h0

Virtual image (on same side of lens)

Real image (on opposite side of lens)

di

NeverAlwaysd0

NegativePositiveVariable

do f

dif

ho

hi

object

image

Thin Lens Equation

fdd i

111

0

=+

Magnification Equation

00 d

d

h

hM ii −==

Example: A converging lens has a focal length of 15 cm. If a light is located 50 cm from the lens, what type of image will be formed and where will it be located?

Analysis:

Required:

Given:

Phrase:

Solution:

LENS EQUATIONS

Magnification

Focal length

Height of image

Height of object

distance from the image to the optical

centre

distance from the object to the optical

centre

Definition

Inverted imageUpright imageM

Diverging lensConverging lensf

When measured downward

When measured upward

hi

When measured downward

When measured upward

h0

Virtual image (on same side

of lens)

Real image (on opposite side of

lens)di

NeverAlwaysd0

NegativePositiveVariable

Example: A converging lens has a focal length of 15 cm. If a light is located 50 cm from the lens, what type of image will be formed and where will it be located?

Analysis:

Required:

Given:

Phrase:

Solution:

A real image is formed 21.43 cm from the lens.

Example: A pencil of height 14 cm is placed in front of a converging lens. An inverted, real image of height 43 cm is seen on the other side of the lens. What is the magnification of the lens?

Analysis:

Required:

Given:

Phrase:

Solution:

LENS EQUATIONS

Magnification

Focal length

Height of image

Height of object

distance from the image to the optical

centre

distance from the object to the optical

centre

Definition

Inverted imageUpright imageM

Diverging lensConverging lensf

When measured downward

When measured upward

hi

When measured downward

When measured upward

h0

Virtual image (on same side

of lens)

Real image (on opposite side of

lens)di

NeverAlwaysd0

NegativePositiveVariable

Example: A pencil of height 14 cm is placed in front of a converging lens. An inverted, real image of height 43 cm is seen on the other side of the lens. What is the magnification of the lens?

Phrase

Solution:

Analysis:

Required:

Given:

The lens has a magnification of -3.07.

Homework

• WB page 54 #1-4

• Textbook page 566 #1-8