What happens to the shadow if the distance from the source to the object is decreased?
Shadow size increases
What is the shadow from a point source called?
What is the shadow from an extended source called?
Shadow from a point source is called: umbra
Shadow from an extended source is called: penumbra
What is the evidence that light travels in straight lines?
- a source of light (sun) casts distinct shadows
- the beam from laser point is straight
What is the evidence that light moves?
it bounces off mirrors (starts at one point and ends in another)
How many rays are coming out of a light source?
very large but NOT ∞ # of rays
Why is it impossible for us to see the beam of light unless there is fog/dust?
Fog/dust scatters the rays of light into our eyes
What is the UMBRA?
Darkest shadow (formed by a point source)
What is the PENUMBRA?
Partial shadow (formed by extended source)
When light strikes an object what can happen?
- Scattered (translucent material)
- Absorbed (thermal energy)
- Transmitted (transparent material)
What was the old theory of the speed of light?
People used to believe that light had an ∞ velocity
What is the current theory of the speed of light?
The speed of light is constant: 2.99 x 10^8 m/s
Represents the cosmic “speed limit” for matter & energy in the universe
Who proved that the speed of light was constant?
Galileo helped out (earlier)
What happens as the distance from the pinhole - screen is changed?
PINHOLE - SCREEN:
- Small distance: small image, high intensity
- Large distance: large image, low intensity (same # rays hitting a larger area)
What happens as the distance from the source - pinhole is changed?
SOURCE - PINHOLE:
- Small distance: large image
- Large distance: small image
What happens when the size of the pinhole is changed?
- Small pinhole: small image, sharp (no overlap), low intensity (fewer rays can go through)
- -* Large pinhole: large image, fuzzy (overlap), high intensity (more rays)
What happens if there are 2 pinholes instead of 1?
- 2 holes = 2 reproductions
- They can be completely separate or they can overlap
What does transparent mean?
almost ALL light passes through → no scattering
What does translucent mean?
SOME light passes through
light is scattered as it passes through & objects on the other side appear fuzzy/unclear
What does opaque mean?
NO light passes through
light is either reflected or absorbed (converted to thermal EQ)
What does reflection mean?
abrupt change in direction
What does absorption mean?
transfer of energy from a wave to the matter that it passes through it
What does transmission mean?
light is able to pass through
What does scattering mean?
When a particle changes in direction as a result of collision with another particle
Will the image from a point source or an extended source be sharper?