The%20electric%20field%20in%20an%20EM%20wave%20traveling%20northward%20oscillates%20up%20and%20down.%20In%20what%20plane%20does%20the%20magnetic%20field%20oscillate?

1
The electric field in an EM wave traveling
northward oscillates up and down. In what plane
does the magnetic field oscillate?
1) In the north - south plane. 2) In the up -
down plane. 3) In the northeast - southwest
plane. 4) In the northwest - southeast plane. 5)
In the east - west plane.
2
E
c
B
3
Recall speed of mechanical waves along an
elastic medium
Tension linear density

E directly pushes charges (connecting distance
charges), conveying the disturbance on one
charge to others B induces back emfs to resist
the changing E-fields

v
while the mutually induced fields guaranteed E?B
Maxwell concluded disturbances in E, B field
lines ripple out at constant speed
4
In 1849 (Maxwells time)
1

311,000,000 m/sec
v
m
e
0
0
and Fizeaus best measurement c315,000,000 m/sec
Maxwell The velocity of the transverse
undulations calculated from the
electromagnetic measurements of MMs. Kohlrausch
and Weber, agrees so exactly
with the velocity of light
calculated from the optical experiments of M.
Fizeau, that we can scarcely
avoid the inference that light consists in the
transverse undulations of
electric magnetic phenomena.
5
The wavelength of microwaves generated by a
microwave oven is about 3 cm. At what frequency
do these waves cause the water molecules in your
breakfast burrito to vibrate ?
1) 1 GHz 2) 10 GHz 3) 100 GHz
1 GHz 109 Hz
6
The magnetrons of microwave ovens are tuned to
2.54 GHz (the natural vibrational energy that
sets water molecules spinning/flipping and
heating up any surrounding food).
2.54 ? 109 Hz ? ? 0.125 meter 12.5 cm
7
Infrared Photography
Infrared photography is used to check heat
insulation of houses in winter. If you look at
an infrared picture of a house which areas would
need better insulation?
1) the bright areas 2) the dark areas 3) need
more information
8
Oxygen O8
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d
Iron Fe26
9
Energy Levels for Hydrogen
10
Atomic Spectra
Blackbody spectrum is continuous
Explaining these phenomena requires and
understanding of the atom
11
Some answers to previous slides
5) In the east - west plane.
In an electromagnetic wave, the E and B fields
are perpendicular to each other and to the
direction the wave propagates.
2) 10 GHz
f v / ? 3 ? 108 m/s / 0.03 m 1010 Hz 10
GHz
1) the bright areas