- Discuss and review how the behaviorof shadows is related to the size and distance of the object from the light source

- Derive a law for the behavior of light in specular reflection

- Learn how colors mix to create white light

TODAY’S OUTCOMES:BEHAVIOR OF LIGHT

This diagram represents a small frosted light bulb, a mask with a large hole in it, and a screen. Light is emitted from all parts of the light bulb. Draw some straight lines representing the paths that light can take. Determine the region on the screen that will be completely dark, the region that will be lit by all parts of the light bulb, and the region that is neither completely dark nor completely lit.

This diagram represents a small frosted light bulb, a mask with a large hole in it, and a screen. Light is emitted from all parts of the light bulb. Draw some straight lines representing the paths that light can take. Determine the region on the screen that will be completely dark, the region that will be lit by all parts of the light bulb, and the region that is neither completely dark nor completely lit.

bright

fuzzy

fuzzy

dark

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Drawing ray diagrams

light source object surface

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You could draw this - but why do we draw it this way?

Consider a simple case - a tiny, “point” light

light source object surface

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No “fuzzy” areas - each spot either gets light or it doesn’t

Let’s add a 2nd tiny light nearby

light source object surface

Let’s add a 2nd tiny light nearby

light source object surface

Let’s add a 2nd tiny light nearby

light source object surface

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Let’s say you’re a fly......

light source object surface

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Let’s say you’re a fly......

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How many lights would the fly see here? 2

Let’s say you’re a fly......

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1How many lights would the fly see here?

Let’s say you’re a fly......

light source object surface

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0How many lights would the fly see here?

Let’s say you’re a fly......

light source object surface

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1How many lights would the fly see here?

Let’s say you’re a fly......

light source object surface

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2How many lights would the fly see here?

Back to the large light.....

light source object surface

Imagine it as a bunch of tiny “point lights” - we’ll just look at the edges...

light source object surface

Imagine it as a bunch of tiny “point lights” - we’ll just look at the edges...

Back to the large light.....

light source object surface

Imagine it as a bunch of tiny “point lights” - we’ll just look at the edges...

Back to the large light.....

light source object surface

Let’s get the fly and ask what it sees....

The whole light source

Back to the large light.....

light source object surface

Let’s get the fly and ask what it sees....

Part of the light source

Back to the large light.....

light source object surface

Let’s get the fly and ask what it sees....

None of the light source

Back to the large light.....

light source object surface

Let’s get the fly and ask what it sees....

Part of the light source

Back to the large light.....

light source object surface

Let’s get the fly and ask what it sees....

All of the light source

Back to the large light.....

What if the light is REALLY far away??

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It becomes like a point sourceagain - the shadow becomessharp again.

All this applies to any source & surfacesource

object

surface

All this applies to any source & surface

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object

surface

light

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lightdark

Margie is correct - an object too close to a wide light source (in this case, the filament), will not project a sharp shadow. Louise could help this scheme by making a shade with “shapes” further from the light bulb, to make sharper shadows on the wall.

Louise has an idea how to decorate her living room for when she hosts the bridge club next week: she will draw hearts and spades on the light bulbs, so that they project these pictures onto the lampshade and the ceiling. Easy to do, cheap, and after the party she can just wash the pattern off. Her neighbor Margie objects, "If that’s going to work, why doesn't the '100 Watts' written on the light bulb show on the ceiling already?" Is Margie right, that this won't work? Or can you tell Louise how to rescue the scheme?

- Shadows grow larger when they are closerto the source

- Shadows from point-like lights cast verysharp shadows

- Shadows from large light sources have a region of “fuzziness” that can be determinedfrom ray diagrams

WHAT YOU ARE EXPECTED TO KNOW:

- Discuss and review how the behaviorof shadows is related to the size and distance of the object from the light source ✓

- Derive a law for the behavior of light in specular reflection

- Learn how colors mix to create white light

TODAY’S OUTCOMES:BEHAVIOR OF LIGHT