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Homework Set 2
From “Seeing the Light” Chapter 2:(starting page 68)
P2, P5, P12, P14, P18, P21, P23, PM2Due: Monday, Feb 16
Geometric optics Geometric Optics: Study of light-
rays based on the assumption that light travels on a straight line
Useful when the wavelength of light is much smaller than the physical sizes. Can explain most phenomena in daily
life!
Light Sources Point source: size small compared
with any other sizes in the problem Small light bulbs, candles, or sometimes
even the sun Light rays travel from the source in all
directions in straight lines Extended source:
Two bulbs, long fluorescent tubes… Light rays travel from all points of the
source in all possible directions.
Shadows When the light-rays are blocked by
an obstacles in the way, shadows are formed on a screen: Did You see your shadow from the sun
light? X-ray pictures We can figure out the location and
shape of shadows by drawing the light-rays.
At night, we are in the shadow of the Earth!.
Shadow and art
Silhouette portraits
Using shadow to show the object in the air.
More examples?Drop shadowShadow playShadow stampingShadow box….
Umbra and Penumbra Two light-sources will create two
shadow, and extended light-sources create infinite many shadows.
Umbra: a region where all shadows overlap, completely dark
Penumbra: the region it is partially dark. When you are in penumbra, you see a
part of the light-source.
Solar Eclipse Eclipses can occur sometime when
there is a New Moon. This is when the Moon passes between the Earth and Sun. Then, the Moon's shadow sweeps across the Earth's surface and we may see some part, or all, of the Sun covered or 'eclipsed' by the Moon. Light-source: sun Obstacle: moon Screen: earth
Total Solar Eclipse
When the moon is closer to Earth, the size of the Moon's disc is the same as that of the Sun's, and the Sun is completely blotted out, resulting in a Total Solar Eclipse at some point on Earth, and a partial solar eclipse in places close to the zone of totality.
Annular Solar Eclipse
When the moon is farthest from Earth, the size of the Moon's disc is slighltly smaller than that of the Sun's, and does not completely cover the Sun in an eclipse. When this happens , a ring of Sunlight surrounds the Moon's disc during the eclipse giving rise to what is known as an Annular Eclipse
Lunar Eclipse: A lunar eclipse takes place when the
Earth passes between the Sun and the Moon. The Earth's shadow falls on the full moon, making it appear like the it's going through a cycle of phases--but in fast motion! A lunar eclipse, from start to finish, takes only a matter of hours--as long as it takes for Earth to "get in" and then "get out" of the way of the light hitting the Moon. Light-source: sun Obstacle: earth Screen: moon
Pinhole Camera
A small, light-tight can or box with a black interior and a tiny hole in the center of one end.
You can design it to accept roll or sheet film. The two ends of the camera are parallel. The end opposite the pinhole is flat so that the film is held in a flat plane.
The pinhole has a cover to prevent light from entering the camera.
Pinhole Camera The light intensity is small. It takes
a long time to take a picture The hole cannot be too big. Or the
picture will be blurred. The hole cannot be too small. Or the
wave property of the light will blurred the picture.