light – a wave, a ray, or a particle?. law of reflection – ray optics view

Light – a wave, a ray, or a particle?

lambda = d/10

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lambda = d/4

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lambda = d

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Law of Reflection – ray optics view

But light’s not really a ray Why can we get away with acting like

it is? Do ocean waves act like rays of light?

What’s the real reason light reflects symmetrically around the normal?

Discussion question: How tall must a flat mirror hanging on the wall be in order for a person to see their feet and their eyes without moving with respect to the mirror?1. As tall as the person2. Half the height of the person3. ¼ the height of the person

Hard WorkToday, many have forgotten the value of work. Some falsely believe that the highest goal in life is to achieve a condition in which one no longer needs to work. President David O. McKay (1873-1970) was fond of saying, "Let us realize that the privilege to work is a gift, that power to work is a blessing, that love of work is success."

Work is not a matter of economic need alone; it is a spiritual necessity.

-- BISHOP H. DAVID BURTON

Reading question: The speed of light in glass is _________ the speed of light in air.1. Less than2. The same as3. Greater than

Snell’s law describes refraction: the bending of light when it enters a medium.

The rolling barrel - a sort of ok-ish analogy that is often

used

The wave physics behind Snell’s law

What changes when the light enters glass?

What stays the same?

There’s actually more than one speed . . .

Dispersion, phase velocity, group velocity

Light enters a piece of plate glass which is 3 mm thick and has an index of refraction of 1.5. It enters the glass at an angle θ1 relative to the normal. It exits the glass at an angle θ3 relative to the normal. Which of the following is true?

1. θ3 is greater than θ1.2. θ3 is less than θ1.3. θ3 is equal to θ1.4. It depends on information I haven’t given

you

Snell’s Law

Consider refraction through three materials.

Now remove the middle material.

3

2

1n1 1

n3 1.5

n2 1.3

˜ 3

1

n3 1.5

n1 1

A. Angle 3 is smaller than beforeB. Angle 3 is the same in bothC. Angle 3 is greater than before

Light is travelling in glass with an index of refraction of 1.5. It strikes the surface of the glass at an angle of 85 degrees from the normal. Some of the light transmits, some reflects. What direction will the two beams travel?

n1 = 1.333

n2 = 1.000

θ1

θ2

θ1

θ2

93% Transmission over a km!

Discussion question: A fish swims below the surface of the water. The observer sees the fish at

A. A greater depth than it really is

B. The same depthC. A smaller depth than it really

is.

Looking at things in a mirror

Virtual image The light does not actually come

from that point—it only looks like it does. You have to look into the mirror to see it.