PHYS-1214-Lecture-21-Spring-2013 - Physics

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18 Οκτ 2013 (πριν από 3 χρόνια και 10 μήνες)

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Mar.
4
t
h
, 20
1
3


PHYS 1214

Chapter 22 (Sections 22
-
1 to 22
-
4
)


Maxwell’s Equations (1865)


1.

Electric fields result from electric charges

(Coulomb’s Law)

2.

Magnetic fields are continuous (no magnetic
charges or monopoles)

3.

Changing magnetic field produces an

electric
field (Faraday’s Law of Induction)

4.

Magnetic field is produced by an electric current
(Oersted, Ampere), or by a changing electric
field (Maxwell’s hypothesis)


Electromagnetic Waves (EM Wave)


1.

No medium required for EM waves

2.

Transverse waves

that

consist of oscillating
electric and magnetic fields, which are
perpendicular to each other and to the direction
of propagation

3.

Electric and magnetic fields are
in phase


Light is an electromagnetic wave with velocity c,
where


(free

space value)




The relationship between the velocity, wavelength
and frequency of an EM wave is the same as a
sound wave








Measuring the speed of light


Angular separation between consecutive 450
notche
s


Δθ=(1/450) rev


Δt=

Δθ/ω=(1/450) rev/[35 rev/s]







Δt=6.4x10
-
5

s


c=2d/

Δt=(19000 m/ 6.4x10
-
5

s) = 3.0x10
8

m/s



Electromagnetic spectrum


EM waves with different frequencies (f), and
wavelengths (

), but same velocity (c).





Visible Light

Produ
ction of Electromagnetic Waves



EM Waves produced by accelerating electric
charges


1.

Charges accelerating in a straight line produce
EM waves in directions perpendicular to
acceleration (donut shaped around charge)

2.

Circling charges (synchrotron radiation)
-
emit
cones of EM waves (visible and x
-
rays).

3.

Oscillating charges and currents
-
dipole
radiation
-
radio waves

4.

Atomic EM waves
-
will discuss later