Electromagnetic Waves in Physics

Put the four laws of electricity and magnetism side by side and they predict something nobody asked for. A changing electric field makes a magnetic field, and a changing magnetic field makes an electric one, and if the arrangement is right the pair can travel together with neither one leading. Working out the speed of that disturbance from two constants measured entirely in the laboratory gives the speed of light, which is how Maxwell realised he had been studying optics all along. The blocks give the written form of the four laws, the wave that follows from them, and the quantities that describe what it carries, its energy, its intensity, and the very small push it exerts when it arrives.

Displacement current between the plates of a charging capacitor

Given

(V m)
(s)

Constant used

Maxwell's equations in integral form

Given

(V m, Wb)
(A)

Constants used

Speed of light from the electric and magnetic constants

Given

(C²/(N m²))
(T m/A)

Constants used

Speed of light in a transparent medium

Given

(m/s)

Electric and magnetic amplitudes in a plane electromagnetic wave

Given

(V/m)
(T)
(m/s)

Instantaneous energy density of an electromagnetic wave

Given

(C²/(N m²))
(V/m)

Constant used

Intensity of an electromagnetic wave from its amplitudes

Given

(V/m)
(T)
(T m/A)

Constant used

Intensity of an electromagnetic wave from the electric amplitude alone

Given

(V/m)
(T m/A)
(m/s)

Constants used

Intensity of radiation from its power and area

Given

(W)
(m²)

Radiation pressure on a perfectly absorbing surface

Given

(W/m²)
(m/s)

Constant used

Radiation pressure on a perfectly reflecting surface

Given

(W/m²)
(m/s)

Constant used

Momentum carried by a burst of electromagnetic radiation

Given

(J)
(m/s)

Constant used

Wavelength and frequency of an electromagnetic wave

Given

(m/s)
(Hz)

Constant used