Transcript Properties of Light

Objective:
1) Distinguish
between wave
fronts and rays
2) Apply the law of
reflection to
solve real world
problems
3) Explain
refraction in
terms of Snell’s
Law and the
index of
refraction
4) Relate color
vision and light
BELLWORK
The table at the left represents
the decibel level for several
sound sources. Use the table to
make comparisons of the
intensities of the following
sounds.How many times more
intense is the front row of a
Smashin' Pumpkins concert than
a. ... the 15th row of the same
concert? b. ... the average
factory?
c. ... normal speech?
d. ... the library after school?
e. ... the sound which most
humans can just barely hear?
• As the car approached with its siren blasting,
the pitch of the siren sound (a measure of the
siren's frequency) was high; and then
suddenly after the car passed by, the pitch of
the siren sound was low
The Doppler Effect and Light
• A moving light source is said to be red-shifted
or blue-shifted.
• If an astronomer describes the wavelength of
a star to be blue-shifted, is the star moving
towards the observatory or away from the
observatory?
Light and the
Electromagnetic Spectrum
• Electromagnetic waves are waves which are
capable of traveling through a vacuum.
• Electromagnetic waves are produced by a
vibrating electric charge and consist of both an
electric and a magnetic component.
• Electromagnetic waves exist with an enormous
range of frequencies. This continuous range of
frequencies is known as the electromagnetic
spectrum
Visible Light
• The visible light spectrum: the type of
electromagnetic wave which stimulates
the retina of our eyes
• The visible light region ranges from
700 nm to 400 nm
• This narrow band of visible light is also
known as ROYGBIV
Vision: photons of visible light carry the
activation energy to bend retinal molecules
(derived from Vitamin A, retinol) from the cisisomer to the trans- isomer. This stimulates the
optical nerve so your brain can interpret photons
of light as colors and shapes to see.
HOW ARE ELECTROMAGNETIC WAVES
DISTINGUISHED FROM MECHANICAL WAVES?
A. They can travel through materials and mechanical
waves cannot
B. They come in a range of frequencies and mechanical
waves exist with only certain frequencies
C. They can travel through a region void of matter and
mechanical waves cannot
D. They cannot transport energy and mechanical waves
can transport energy
E. They have an infinite speed and mechanical waves
have a finite speed
INTERPRETING THE
ELECTROMAGNETIC SPECTRUM
1. Which region of the electromagnetic
spectrum has the highest frequency?
2. Which region of the electromagnetic
spectrum has the longest wavelength?
3. Which region of the electromagnetic
spectrum will travel with the fastest speed?
4. Which color of the visible light spectrum has
the greatest frequency?
5. Which color of the visible light spectrum has
the greatest wavelength?
EXAMPLE
The Bohr model of the hydrogen atom consists of a proton of
mass 1.67x 10-27 kg and an orbiting electron of mass
9.11x10-31 kg. In one of its orbits, the electron is 5.3 x10-11 m
from the proton and in another orbit it is 10.6 x10-11 m from the
proton.
A. What color of light is emitted by the electron during this
transition when it’s wavelength is 656 nm?
B. Given that the wavespeed for light = speed of light, c and
c=f, at what frequency does the lightwave vibrate?
C. If the electron jumps from the larger orbit to the smaller one,
what is the change in the gravitational potential energy of
the atom?
D. The energy transmitted by a wave corresponds to its
frequency. E = hν = hf… How does this energy compare to U?
A) The color associated with this wavelength is
red (in the Balmer series for hydrogen)
B) The frequency is found by
f = c/
= (3.00 x 108 m/s )/ (656 x 10-9 m)
= 4.57 x 1014 Hz = 4.57 x 1011 kHz
C) The change in gravitational potential energy,
DU = U1 – U2 .
Therefore, the atom loses -9.6x10-58 J of potential
energy so the light emitted has 9.6x10-58 J of
Energy.
D) E = hν
= (6.63 x 10-34 Js)(5.13 x 1014 s-1)
= 3.03 x 10 -19 J
Where did all the energy go? Why is some of the
gravitational potential energy “lost”?
INDEPENDENT PRACTICE
• P. 498- 499; 3, 6, 8, 10, 11, 12, 16, 19, 20, 26
• P. 684; 70, 71, 72, 77, 78, 80