The energy wavelength equation is: E = hc/I, where E indicates energy measured in joules, I indicates wavelength in meters, c is the constant for how fast electromagnetic radiation (light for all extensive purposes) travels and h is Planck's constant. For reference, Planck's constant is h = 6.626 x 10-34 joules/second, and the speed of light in a vacuum is c = 3.0 x 108 meters/second.
When approaching energy (E) and wavelength (l) relationships, we have to recognize two constants that come into play, the speed of light and Planck's constant. These constants were derived from Max Planck in 1900 using black body radiation, where he discovered that all energy is a multiple of 6.626 multiplied by the frequency of the wave of light. Energy is therefore quantized; it is always a multiple of a single packet of energy.
According to Kent Chemistry, a typical question is: How much energy does a photon of red light with a wavelength of 690 nanometers have (1 meter = 109 nanometers)?
First, convert nanometers to meters, as l is wavelength in meters: 690 nanometers (1 meter/10^9 nanometers) = 6.90 x 10^-7 meters. Next, plug all known values into equation formula: E = hv/I, or E= (6.626 x 10^-34 joules) (3.0 x 10^8 meters/second)/6.90 x 10^-7 meters. Solve for E: E = 2.88 x 10^-19 joules.