5.1. Properties of Light http://www.ck12.org
c =λνIf c is expressed in meters per second, the wavelength must be expressed in meters.
Example 5.1
The brilliant red colors seen in fireworks are due to the emission of light from strontium salts such as Sr(NO 3 ) 2 and
SrCO 3. Calculate the frequency in Hz of red light with a wavelength of 6.50× 102 nm.
Answer:
λν= c
ν= c/λ= (2.998× 108 m/sec)/(6.5× 10 −^7 m) = 4.61× 1014 sec−^1 = 4.61× 1014 HzElectromagnetism
Much of our understanding of the light and the way it behaves is based on the work of Michael Faraday, James
Maxwell, and Heinrich Hertz. In 1845, the English chemist and physicist Michael Faraday (1791–1867) discovered
that light exhibited magnetic properties. His early experiments measured what happened to light when passed
through magnetic fields. Following Faraday’s work, the Scottish physicist and mathematician James Maxwell
(1831–1879) studied electromagnetic radiation and light. Maxwell calculated the speed of light, which was later
confirmed by other scientists to be the very value Maxwell proposed. From his work, Maxwell inferred that light
was probably a transverse electromagnetic wave (Figure5.1). He published this conclusion in 1873.
FIGURE 5.1
The image shows light as a transverse
wave. It consists of oscillating magnetic
and electric fields that are perpendicular
to each other and to the direction in which
the light is traveling.The Electromagnetic Spectrum
In 1888, shortly after Maxwell published his findings, German physicist Heinrich Hertz (1857–1894) confirmed
Maxwell’s inference, showing that light was indeed an electromagnetic wave. Hertz extended Maxwell’s work and
produced electromagnetic radiation with wavelengths that were not in the visible part of the spectrum. In fact, visible
light makes up only a very small part of the entire electromagnetic spectrum (Figure5.2).
Example 5.2
Which type of light has a longer wavelength: red or blue?
Answer:
As is shown inFigure5.2, red light has longer wavelength than blue light. It is to the left of blue light in the diagram.
Example 5.3
Based on what is displayed in theFigure5.2, what is the relationship between wavelength and frequency?