The propagation of light

The propagation of light - Maxwell's equations at speed c...

This preview shows pages 1–2. Sign up to view the full content.

The propagation of light. We can conclude from Maxwell's equations that light is in fact an oscillation of the electric and magnetic fields that propagates through free space with velocity c = 1/ . Moreover, the electric and magnetic fields are always mutually orthogonal and always in-phase. Since electric and magnetic field have an associated energy, their propagation causes the transport of energy and momentum. For this reason it is possible to calculate the energy density (energy per unit volume) of an electric or magnetic field. In SI units these turn out to be: u E = u B = Since μ 0 = 1/ ε 0 c 2 and | in SI units, then u B = u E . This should not be a surprising result--it simply says the energy is divided equally between the electric and magnetic fields. The total energy u is just u = u E + u B = 2 u E = ε 0 E 2 = . Now the wave is propagating in a direction perpendicular to both the electric and magnetic fields (this can be proved from

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Maxwell's equations) at speed c . Therefore, the power incident on an area perpendicular to the direction of travel will have an amount of energy flow through it every second of uc . This can be seen from the dimensions of energy/volume × distance/second = energy per area per second. This is the incident power, S . Thus, S = uc = = c 2 ε EB . We can express this more usefully as a vector , perpendicular to and and normal to the surface across which the power per unit area is being calculated. This gives: This is called the Poynting vector. Figure %: Direction of propagation of an electromagnetic wave. Thus light is a form of electromagnetic radiation, just like radiowaves, microwaves, infrared rays, X-rays, gamma rays and cosmic rays. It has frequencies in the range 3.84×10 14 Hz to 7.69×10 14 Hz, which corresponds to wavelengths of 780 to 390 nanometers....
View Full Document

{[ snackBarMessage ]}

What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern