Unit V - Modern Physics - 20th Century
Physics of the 20th century has given us tremendous amount of knowledge about:
¨
the fundamental _________________________________
¨
_______________________________
I.
Dual Nature of
Light- Light appears to exhibit
the characteristics of either a
____________or ________________in different
situations.
A. Review - 19th Century - Experiments supporting wave theory
1)
Interference - "_____________________________." - constructive/
destructive
2)
Polarization - "Filtering of Light - Light waves have _________
3)
Diffraction - ___________________________________behind a barrier
4)
Doppler - Color Shift of Light - _________________________
B.
Experiments Supporting _____________________________of Light (20th century)
An experiment in the late
1800's baffles scientists.
Light is not acting like a _________________!
The
experiment that scientists can't explain is called…
The
__________________________ Effect-
when light is exposed to
the
surface of certain __________it absorbs
the light energy and uses
it
to eject_______________
Emitted electrons are called _____________________
____________other electromagnetic
radiation
The light’s energy causes the emission of
____________________.
Unexpected Results!!!:
1.
When you brighten the light source – Get _____________________
Intensity of light (Brightness)
... but not
_______________________________________!!!!
K.E. of
Photoelectrons
Intensity of light (Brightness)
Results
Contradict Wave theory!!
Should Increase _____________________________________________
Emitted
- It Didn't!!
The
K.E. of photoelectron was ACTUALLY determined by:
a)
__________________ of light
(color)
b)
nature of
______________________________
A
typical Plot of Frequency of Light
versus KE of Photoelectron
fo _______________________ frequency - frequency below which
_________________ will be emitted
Summary
1. Photoelectric
Effect - Proved to us that light sometimes can act like a
____________
2. What's
the photoelectric effect? - When
you shine light on certain
metals they give off
________________________
3.
Changing the
light in this experiment produced unexpected
results
|
When you brighten light…. |
When you increase frequency Of light used… |
|
Get
__________________________ |
You increase the ___________of photoelectrons |
4.
Threshold Frequency - ' DOORWAY frequency '
Below Threshold - Above Threshold -