Charge vibrates

1
Charge vibrates linearly along the direction
illustrated. This oscillating dipole emits
transverse waves preferentially in what
direction?
1
2
3
Waves are transmitted equally in all directions
4
5
2
sin (90o- ? )
h
y
?

• sin?
• -sin?
• cos?
• (4) -cos?
• (5) tan?
• (6) -tan?

x
3
The magnetron of a microwave horn generates a
horizontally varying B-field and oscillating
vertical E-field. We found which of the
aluminum gratings below let the microwaves pass?

1
2
4
If waves A and B are superposed (that is, their
amplitudes are added) the resultant wave is
A
B
A)
B)
C)
D)
5
Phase
Phase refers to the relative position of the wave
crests of two waves
6
The two waves shown are A) out of phase by
180o B) out of phase by 90o C) out of phase
by 45o D) in phase
7
Destructive interference occurs when the two
waves arriving at the same point at the same time
are 1) out of phase by 180o 2) out of phase
by 90o 3) out of phase by 45o 4) in phase 5)
could be any of these
8
Imagine two light sources emitting waves of 1
meter wavelength in phase. The waves from
these sources meet at a distant point. Wave 1
travels 2 m to reach the point wave 2 travels 3
m. When the waves meet, they are A) out of
phase by 180o B) out of phase, but not by
180o C) in phase
9
Answers to preceding multiple choice questions
4
See Lecture 24s descriptions of an oscillating
dipole!
h
90o-?
y
?
sin (90o- ? ) x/h x/h cos?
(3) cos?
x
2
The vertical strips act as antenna offering free
electrons to be driven by the Vertical
E-fieldabsorbing microwave energy. The
horizontal strips are not effective antennas and
let the microwaves pass through.
C)
B) out of phase by 90o
1) out of phase by 180o
C) in phase
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