Geometric Optics vs. ‘the wave’

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# Geometric Optics vs. ‘the wave’ - PowerPoint PPT Presentation

Geometric Optics vs. ‘the wave’. ‘plane’ traveling wave. ( Apple &gt;&gt; l ). A light ray: IN. Rough surface. A light ray: IN. Diffuse reflection:. A light ray: IN. Reflected light rays: OUT. Distinguishing Objects. Diffuse reflection. Diffuse reflection:. Diffuse reflection.

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Presentation Transcript

Geometric Optics vs. ‘the wave’

‘plane’ traveling wave

Rough surface

A light ray:

IN

Diffuse reflection:

A light ray:

IN

Reflected light rays:

OUT

Distinguishing Objects

Diffuse reflection

Diffuse reflection:

Diffuse reflection

No focusing:

Belly and nose undistinguishable!

Use a lens to ‘focus’:

Belly and nose distinguished !

Use a lens to ‘focus’:

Belly and nose distinguished !

How to focus divergent light rays?

Start: Use reflection off of smooth surfaces (mirrors) of special shapes.

Flat mirror

Where is F ?

• must
• be “small”!

Image ?

Object

Image ?

Object

Image ?

Object

Image ?

Object

Image

Image ?

Object

Image

Image ?

Object

Image

Image ?

Object

Image

For a concave mirror: InvertedReal Image

Convention: m < 0 for inverted image!

Example: A cute, baby chick is standing 10 ft in front of a concave mirror of radius 5 ft. Where is its image and how big?

Example: A cute, baby chick is standing 10 ft in front of a concave mirror of radius 5 ft. Where is its image and how big?

Example: Now, the cute, baby chick is standing 5 ft in front of a concave mirror of radius 5 ft. Where is its image and how big?

Example: Now, the cute, baby chick is standing 5 ft in front of a concave mirror of radius 5 ft. Where is its image and how big?

Example: Now, the cute, baby chick is standing 3 ft in front of a concave mirror of radius 5 ft. Where is its image and how big?

Example: Now, the cute, baby chick is standing 3 ft in front of a concave mirror of radius 5 ft. Where is its image and how big?

Example: Finally, the cute, baby chick is standing 1 ft in front of a concave mirror of radius 5 ft. Where is its image and how big?

DEMO

Example: Finally, the cute, baby chick is standing 1 ft in front of a concave mirror of radius 5 ft. Where is its image and how big?

“Virtual” image !

DEMO

‘Focal length’ ?

• must
• be small!

For a convex mirror: UprightVirtual Image

We can use the

same formulae

for a Concave mirror

If we use

Note di will always be negative:

Example: A cuter duck is standing 10 ft in front of a convex mirror of radius 5 ft. Where is its image and how big?

Example: A cuter duck is standing 10 ft in front of a convex mirror of radius 5 ft. Where is its image and how big?

Quack!

Mirror summary:

CONCAVE

CONVEX

So …

So …

Image

Object

Image virtual: di < 0

do > f

real, inverted

Image upright m > 0

virtual, upright

do < f