When a wave on a string encounters a free end, the reflected wave does
NOT have to destructively interfere with the incoming wave. There is NO
phase shift on this reflection.
When light is incident on a SLOWER medium (one of index of
refraction higher tha
How do we make light?
Heat and Light: Incandescent Lighting
(5-10% efficient)
Atoms and Light: Fluorescent Lighting & LEDs
(20-40% efficient)
Well review Heat and Light first. Later in this part we will consider Atoms
and Light.
Heat loss by radiation was
1/fobj = 1/s1+ 1/(27.5 cm)
1/(2.778 cm) = 1/(2.5 cm) + 1/(-25cm)
30 cm = 27.5 cm + 2.5 cm ,
and
-100 = (27.5 cm/s1)*(-25 cm/2.5 cm).
Although the first equation has two unknowns, the fourth equation only has
one, so we can solve for s1:
-100 = (27.5 cm/s1
What DOES happen?
Look at a very bright laser beam
going through a vertical slit.
(A laser has one frequency
unlike white light.)
We will consider this situation
but only after we consider another:
the DOUBLE SLIT experiment:
Note that along the solid gre
At this point, lets fill in the knowns into the four equations:
1/fobj = 1/s1 + 1/s1,
1/feye = 1/s2 + 1/s2, or 1/feye = 1/s2 + 1/(-25cm)
L = s1 + s2 ,
and
M = (s1/s1)*(s2/s2), or -100 = (s1/s1)*(-25 cm/s2).
There are many ways to choose two unknowns. We c
For other types of light (based on the technology used to make the light):
radio:f is 1MHz for AM, 100 MHz for FM
so l is
1 km to 10 cm
microwaves/radar:
infrared:
visible
ultraviolet
x-ray & g ray
10 cm to 1 mm
1 mm to 700 nm
700 nm to 400 nm
400 nm to 1
So far, the wave theory has explained things very well:
speed of light
different colors
reflection
refraction (dispersion, thin lenses)
To look at the next property, shadows, we need to review the wave idea a
little bit.
Sine waves are nice.
Other types o
1.22 n l = D sin(qn) where q1 = qlimit ,
so 1.22 l = D sin(qlimit) ; also sin(qlimit) tan(qlimit) = h/s. Therefore, 1.22 l
D*h/s, or h 1.22 l*s/D where h is the smallest size that is resolvable.
This means that h l .
microscopes: smallest size = l = 500
Consider the (ideal) resolving ability of the eye
Estimate D, the diameter of the pupil
Use l = 550 nm (middle of visible spectrum)
Now calculate the minimum angle the eye can resolve.
Now calculate how far apart two points of light can be if they are 5
A far sighted person can see things clearly if they are far away, but has
trouble focusing on things close.
When things are close, the eye has to bend the light a lot in order to focus,
and the far sighted persons eyes have trouble with that. When things