Days of the week(always go to 1st hour every day)

• Monday Guided Study after 2nd hour• Tuesday 1st 25 minutes is Quiet Study• Wednesday Advisory after 2nd hour• Thursday 1st 25 minutes ReAdvisory• Friday Guided Study after 2nd hour

Class Notes..9.13.11. Linear Propigation

Handout : worksheet pkt.Handout safty sheets and syllabus

HAND IN : Camera Obscura Lab due by 3 pmif you started late, ask for a book…

9.13.11.Book Notes chap 16Glencoe Book Pages 373-3889.13.11.Book questionsGlencoe Book Pages 389-399 (1-15, 19, 20, 24,25)

Determining the speed of light

Foucault used more precise timing

• , allowing shorter distance and measurement of v in water and other transparent materials; v was shown to be less than c, contrary to Newton's view. We now know that v=c/n, where the refractive index n can be measured by refraction experiments.

1675 the speed of light was measured by Ole Roemer

• Astronomers have always been extremely accurate. There was a discrepancy in the times of eclipses of the moons of Jupiter!

An image of Jupiter and its moon Io (left) from the Cassini probe.

Question #1…Notice: Io is in the same position compared to Jupiter

• Near side of sun on July 1 and Far side of Sun on January 1.• Longer distance for light to travel.• Takes 22 minutes longer

Hewitt Light Worksheet #1 Roemer’s measurement of the Speed of light

• Diameter of earth’s orbit: 300,000,000 km

• Time difference for this distance is 22 minutes

• Use the equation d=vt or v=d/t

• Use this information to find the speed of Light in km /sec

Hewitt Light Worksheet #2 Frequencies and wavelengths of EM spectrum

all of these types of waves travel at the speed of light, which is 3 x 105 km/s or 3 x 108 m/s

“Light waves”

Skip #3 for now…..• Hewitt Light Worksheet #3

Solar Eclipse THE MOON IS BETWEEN THE EARTH AND SUN

• A solar eclipse is a shadow of the moon on the earth

Hewitt Light Worksheet # 4a• Solar eclipse• Notice the way the

rays are drawn

This is what a full solar eclipse would look like

LUNAR Eclipse THE EARTH IS BETWEEN THE SUN AND MOON

Hewitt Light worksheet#4 b. Lunar Eclipse: EARTH IS BETWEEN THE MOON AND THE SUN

Total lunar eclipse

Partial lunar eclipse

#5 UMBRA IS THE DARKEST PART OF THE SHADOW AND THE PENUMBRA IS THE LESS

DARK PART OF THE SHADOW

Positions of the moon for solar and lunar eclipses

"Why don't extended sources of light make sharp shadows?"

• What is the difference between a point source of light and an extended source of light? How come when a point source of light is used to cast a shadow, the shadow is totally dark whereas with an extended source of light an umbra and penumbra result? Sally's explanation An extended source is like a frosted light bulb -- light comes from many places, and at any point in space there is light going different directions. A point source is a very small source, so that now there is just one point that the light comes from. Of course, all light sources are to some extent extended, though I have one made from a laser pointer for which the source certainly is very tiny. For many purposes, an unfrosted light bulb is a good approximation to a point source. As you observe, point sources give sharp shadows, while extended sources give fuzzy-edged ones (that is already the distinction between them!). Here is a picture that explains how this comes about: Light travels in straight lines from the source, in many directions. In the top picture the blue object is making a sharp-edged shadow on the screen, because either there is a path for light to take from the light source to the screen or there is not. I have indicated the region of (total) shadow by shading it, and indicated the part of the screen that is lit by coloring it red. In the bottom picture I have drawn some lines from various parts of the light source. We observe that some parts of the screen are illuminated by all of the light source (colored in red again), some regions receive no light at all (shaded again), and some regions are illuminated by part of the light bulb but not all of it. I colored this part of the screen purple. Here are pictures of a clear bulb (almost a point source) and a frosted bulb (an extended source), and shadows made by them. On the subsequent pages, you can see what a bug sitting on the screen would see, looking back at the bulb. This is another way of understanding why the extended source has a penumbra that is neither light nor dark -- these regions can only see part of the light bulb.

Which bulb produced which shadow?

SOLAR ECLIPSE