aphy201 10/24/2015 1 22.1 maxwell’s equations 1865 – james maxwell unifies electricity and...
TRANSCRIPT
APHY20104/21/23 1
22.1 Maxwell’s Equations
1865 – James Maxwell unifies electricity and magnetism and shows that their fields move through space as waves.
He calculated that the EM waves travel at the speed of light so they must be a type of light.
1887 – Heinrich Hertz generates and detect EM waves for the first time
APHY20104/21/23 2
22.2 Production of Electromagnetic Waves
Energy is stored in E and B
Magnitude of E and B are
At large distances, the waves areplanar or flat.
...ΔtΔE
ΔtΔB
ΔtΔE
r1
APHY20104/21/23 3
22.2 Production of Electromagnetic Waves
EM waves are transverse Amplitude is perpendicular to wave motion
EM waves travel at c = E/B = 3 x 108 m/s
APHY20104/21/23 4
22.3 Light and the Electromagnetic Spectrum
Speed = Frequency * Wavelength c = f λ
APHY20104/21/23 5
22.3 Light and the Electromagnetic Spectrum
5
X-ray Visible
Polarized Radio
APHY20104/21/23 6
22.6 Momentum Transfer and Radiation Pressure
Remember that
Maxwell showed that where a = 1 to 2
Since and then
ΔtΔp
F
cUa
p
AF
Parea
powerintensity
cIa
P
APHY20104/21/23 7
22.6 Momentum Transfer and Radiation Pressure
APHY20104/21/23 8
22.7 Wireless Transmission
Radio and wireless telegraph (1890’s)
The FCC and broadcast “bands”
APHY20104/21/23 9
22.7 Wireless Transmission
APHY20104/21/23 10
22.7 Wireless Transmission
APHY20104/21/23 11
22.7 Wireless Transmission