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Lecture 13

# PHYSICS 7E Lecture Notes - Lecture 13: Christiaan Huygens, Electromagnetic Radiation, Geometrical OpticsPremium

Department
Physics
Course Code
PHYSICS 7E
Professor
GUERRA, A
Lecture
13

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PHYSICS 7E - Lecture 13 - Electromagnetic Waves / The Nature of Light
Momentum
Electromagnetic waves transport momentum as well as energy
As this momentum is absorbed by some surface, pressure is exerted on the surface
Assuming the wave transports a total energy U to the surface in a time interval , thetΔ
total momentum is for complete absorption/cp =U
Pressure and Momentum
Pressure, p, is defined as the force per unit area
/Cpav =Sav
For complete absorption
An absorbing surface for which all the incident energy is absorbed is called a
black body
S/Cpav = 2 av
For complete reflection
The Nature of Light
Before the beginning of the nineteenth century, light was considered to be a stream of
particles
Christiaan Huygens argued that light might be some sort of a wave motion
Maxwell asserted that light was a form of high-frequency electromagnetic wave
Thomas Young (1801) provided the first clear demonstration of the wave nature
of light
Einstein (in 1905) proposed an explanation of the photoelectric effect that used the idea
of quantization:
Dual Nature of Light, photons, E=hf
The Nature of Light
Light has properties of both waves and particles. The wave model is easier for explaining
propagation, but some other behavior requires the particle model
The rays are perpendicular to the wave fronts
The Ray Model of Light
Light very often travels in straight lines
We represent light using rays, which are straight lines emanating from an object. This is
an idealization, but is very useful for geometric optics