The Lens Equation

What is the lens equation?

When we put an object in front of a lens mirror, where will the images of this object occur?

Convex Lens

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How can we know the location of the image?

The lens equation will help us to solve all these problems

Definition:

do=Distance from the object to the optical centre.

di=Distance from the image to the optical centre.

ho=Height of the object.

hi=height of the object.

F=Focal length of the lens; distance from the optical centre to the principal focus.

Also….. The focal length (f) is the same whether it goes to F or F’

So now, let’s talk about the first lens equation which is mention in the textbook.

This equation is called “Thin Lens Equation”. It is usually use to calculate the relationship between the distance from the object to the lens and the distance from image to the lens.

Here is an example for “Thin lens equation”.

The distance from a candle to the converging lens is 24 cm. The focal length of this type of lens is 8 cm, so what is the distance from the mirror to the image?

24cm

_______________________________________________ F 8 cm 8 cm

G: do=24cm, f=8cm, di=?

R: di=?

S: 1/24+1/di=1/8

1/di=1/8-1/24

1/di=3/24-1/24

1/di=2/24

di=12

S: The distance from the mirror to the image is 12 cm.

The second equation in the textbook is the Magnification equation. This equation can be state as-------

When you compare the size of the image with the size of the object, you are determining the magnification of the lens.

The magnification equation relates to the distance and height of an image or objects and defines what M is, which magnification is.

hi (height of the image) and ho (height of the object) are positive when measured upward from the principal axis and negative when measured downward.

Also the magnification is positive for an upright image and negative for and

inverted image.

Here is an example for the magnification equation. (Brain storming)

A person of height 1.6m is standing in front of a diverging lens. An upright, virtual image of height 0.8 m is noticed on the same side of the lens as the person. What is the magnification of the lens?