- Review the formation of images by positive lenses

- Develop a model to explain the phases of the moon

- Work toward completing review problems for light

TODAY’S OUTCOMES:BEHAVIOR OF LIGHT

At the movie theatre they use a lens and small pictures in each frame of the film to project really big pictures on the screen. Describe how you could change the system you have been working with to project even larger images that are very big and in focus.

Central to the last activity was the ability to understand image formation

every point on the object produceslight in all directions -to keep it “simple” we only consider the tipof the object

to have a focused image, thelight rays from a point on theobject must converge at a single point

object

image

Light rays can be reversed and followthe same path:

If you place the object at the image distance, the image will move to theobject distance!

object

image

Light rays can be reversed and followthe same path:

If you place the object at the image distance, the image will move to theobject distance!

object

image

In your last lab, you started with a far-away screen (about 1 m)

image when lens close to object

object image

You saw 2 images - the other is just the same situation, reversed

image when lens close to screenobject image

When the screen moved closer to the object; we needed to move the lens further from the object or screen:

image when lens close to object

image when lens close to screen

These diagrams show what happens when the screen moves closer to the object.

object

object

image

image

If you move the screen closer to the object, you reach a point where the image size equals the object size.

Then, the 2 images merge together - you cannot get the screen any closer and stay in focus!

lens halfway between object, screen

lens halfway between object, screen

object

object

image

image

Let’s pull the screen back away from the object...

object

object

image

image

Let’s pull the screen back away from the object...

object

image

image

object

Let’s pull the screen back away from the object...Back to starting distance again:

The distance between the lens and object or screenwas close to (but not quite) equal to the focal length

focal length

focal length

The long light beams are close to (but not quite)parallel

object

image

image

object

If you separated the object and screen by a HUGE distance

focal length

focal length

Beams become (for all practical purposes) parallel.

You used this (bottom) method to find the focal length.

object

object far away

image far away

image

At the movie theatre they use a lens and small pictures in each frame of the film to project really big pictures on the screen. Describe how you could change the system you have been working with to project even larger images that are very big and in focus.

3) You need an easy way to finely adjust the location of your lens along the projection line, because its distance from the object will control the focus of the image.

4) You will need a brighter light source, because the lightwill be spread out over a huge screen.

5) You will need as large a lens as possible, to allow more light to be projected on the screen.

2) The lens will need to be close to the source image, but not as close as the focal length.

1) You need much more distance between the source object and the screen.

- How light coming from a point on an objectconverges to a point on an image

- Size of an image and focus is a function of the placement of the lens between the object and image

- Where to place a lens to produce larger and smaller images

WHAT YOU ARE EXPECTED TO KNOW: