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Lecture series for Conceptual Physics, 8th Ed.
1
Electromagnetic Waves
p452
Shaking a stick in water produces waves.
Shaking a charged stick in space produces
electromagnetic waves.
The moving stick is an oscillating current…
which produces an oscillating magnetic field…
which produces an oscillating current.
ETC.
2
Electromagnetic Wave Velocity
p453
Light has a constant speed because of the
Law of Conservation of Energy.
The oscillating E-field creates the
oscillating B-field and so on…
If the E-field oscillation were weaker,
then the B-field would be weaker and then the next Efield would be weaker and then…and then.
James Clark Maxwell calculated the speed that light would
have to travel in order to insure this mutual self inductance.
He solved one the the “mysteries of the
universe”, light was
3
On a date with his fiancé that evening he remarked
that he was the only person in the world who knew
what starlight was.
The electromagnetic Spectrum
p454
4
More on the E-M Spectrum
Our eyes are sensitive to a small portion
of the EMSpec. called “visible light”.
We have gadgets that produce and
receive other EM waves.
p455- “the universe is a dense sea of radiation in
which occasional concentrates are suspended.”
Recall that v = f 
Light is a wave, so now, c = f .
Where c is the speed of light, 300,000 km/s…
f is the frequency in Hertz…
 is the wavelength in meters.
5
Transparent Materials
p456
Here’s a clever analogy:
Sound waves make the next tuning fork oscillate
if the tines oscillate at that frequency .
The frequency of visible light is more than 1014 Hz.
Electrons can vibrate at that frequency.
Remember that this is just a model.
In the ultraviolet range glass electrons resonant
with UV waves and generate heat.
In the IR range, molecules of glass resonate and produce heat.
In the visible range glass electrons can absorb and re-emit
photons without heating up.
6
More on Transparent Materials
A photon enters
the glass.
It is absorbed and re-emitted straight
ahead at intervals.
In the glass light travels slower than in air, 0.67c.
7
Check out BQ p 458.
Opaque Materials
p 458
Most things are opaque. They absorb light
without re-emission. They warm up.
The free electrons in metal allow photons to be
absorbed and re-emitted as a “bounce.”
8
Does 70% of the focusing.
Relaxed does 30% for the
“infinity” setting.
Page 462
Lens also accommodates…
The muscles around it squeeze it into a
more spherical shape to bring close
objects into focus.
The “blind spot” is surprisingly apparent
when you stare at the dot with your right eye
from the right distance.
Rods- black/white
Cones- color
Cones are more
concentrated at the fovea.
9
Peripheral vision
Iris changes to make
pupil large or small.
Size of pupil is affected by
emotions as well as light
intensity.
Hence, a candle-lit meal.
Here’s another thing about your vision:
Both sides are equally bright.
Don’t see it? Cover the middle. p465
AND, lastly…
10
The end