4.64.6

LensesLenses- Real Images- Real Images

(p346-349)(p346-349)

LensesLenses- Real Images- Real Images

(p346-349)(p346-349)

What is a Lens?• A lens is a thin, transparent piece of glass or plastic

that has at least one curved side.

• The curved side or sides may be concave or convex.

• There are 2 types of lenses

Converging Lens Diverging Lens

What Do Lenses Do?• Lenses come in many sizes and shapes and are made

for many purposes.a) the eye

b) camera

c) telescope

What Do Lenses Do?d) eyeglasses e) magnifying glass

What Do Lenses Do?• Lenses can change the appearance of objects, making images sometimes appear

- larger or smaller than the object

- upside down

- distorted

• Lenses can focus light because of refraction.

• Light refracts when entering and leaving a lens.

What lenses do you use in your life?

Converging Lenses• Also called convex lenses.

• When parallel rays pass through a converging lens, the rays all meet at one point on the other side of the lens.

• This point is the focal point (F).

Diverging Lenses• Also called concave lenses.

• When parallel rays pass through a diverging lens, the rays move apart.

Diverging Lens

1) Rays parallel to principal axis (PA) pass through F.2) Rays through centre of the lens are not refracted.3) Rays through F ‘ emerge parallel to principal axis.

F´

F

Object

PA Image

Ray Diagrams for Converging Lenses

Image for Converging Lenses (LOST)Recall that images have 4 key characteristics:

Location

• Is the image distance shorter or longer than the object distance?

• Is the image behind or in front of the lens?

Orientation

• Is the image oriented in the same direction as the object?

• Is it upright (right side up) or inverted (upside down)?

Size (or Magnification )

• How big is the image compared to the object?

• Is it larger or smaller?

Type

• Is the image real (the rays meet) or virtual (the rays must be extended backward to meet)?

Copyright © 2010 McGraw-Hill Ryerson Ltd.

The characteristics of the image of an object placed beyond F of a converging lens are:

(L) the image is farther from the lens than the object is (O) the image is inverted (S) the image is larger than the object (T) the image is real

So, what does that look like?

Let’s Try This: Where is the Object?

Wrap UpLet’s see that again

Finding focal point of converging lens (p 346)Ray Diagram Activity 4.21 (p349)

WB p140-142

4.64.6

LensesLenses- Virtual Images- Virtual Images

(p350-351)(p350-351)

LensesLenses- Virtual Images- Virtual Images

(p350-351)(p350-351)

Warm Up - Recap

Activity 4.21 (p349)Using BLM 4-20 complete- “Do” #1-5- “Find” #1-2

Let’s Try This: What kind of image?

The characteristics of the image of an object placed between F and a converging lens are:

(L) the image is farther from the lens than the object(O) the image is upright(S) the image is larger than the object (T) the image is virtual

The first lens known to be used was a converging lens called a reading stone.

Reading stones formed images that were upright and larger than the object.

Magnifying glass- Try it yourself !

If the object is between the focal point (F) and the converging lens, a larger (magnified) upright image is formed.

Remember that when the object was outside the focal point (F), an inverted image was formed.

Wrap UpConverging lens (p351)Text p 350

- LC #1-3WB p143

4.64.6

LensesLenses- Applications- Applications

(p357)(p357)

LensesLenses- Applications- Applications

(p357)(p357)

Copyright © 2010 McGraw-Hill Ryerson Ltd.

Science at Work

Applications – Optical Devicesa) Eyewear

- farsightedness (hyperopia)- use converging lens

- nearsightedness (myopia)- use diverging lens

Applications – Optical Devicesb)Telescope

Applications – Optical Devicesc) Microscope

Wrap Up

WB p143 BLM 4-3