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

Electronics - Devices

Oct 18, 2013 (5 years and 5 months ago)

102 views

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

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.

-
emit
cones of EM waves (visible and x
-
rays).

3.

Oscillating charges and currents
-
dipole