# LIGHT

Q. Light is measured in wavelengths.  What does wavelength mean?

A. The wavelength is the measured distance from one wave crest to the next wave crest.  Light is usually measured in Angstroms or nanometers. (click for larger image)

Q. What is an Angstrom?  How long is a nanometer?

A. In the measure of light, Angstrom and nanometer are used interchangeably.  They are both measurements of length. A nanometer is one billionth of a meter.  An Angstrom is equal to 10 nanometers.   A billionth of a nanometer is hard to imagine.  A sheet of paper is 0.1 millimeter.  There are one hundred million nanometers in .1 mm.  (a nanometer is100,000,000 times less than the thickness of a sheet of paper)

Q. How do scientist measure the wavelength of light?

A. There are different methods, but even students (older or more advanced) can measure the wavelength of light.  See this website for instructions. http://www.practicalphysics.org/go/Experiment_124.html;jsessionid=alZLdQlAHb1

Q. Does light change speed?

A. Yes, and No!  Light travels at a constant speed through a transparent medium, however, the speed of light is different through different media.  Light is fastest in a vacuum and slows progressively through air, water, and glass.

Q. Can light be stopped?

A. Yes.  Many materials stop light. The light that is stopped, as on an opaque black surface, is turned into energy as heat.  Recently scientist have been able to stop light in a gas.  Here's an article about it: http://science.nasa.gov/headlines/y2002/27mar_stoplight.htm

Q. What does frequency mean?

A. Each color of light has its own frequency.  The frequency is the number of vibrations per second.  Visible light vibrates between 4.3 x 1014 and 7.5 x 1014 cycles per second, often expressed as Hertz (Hz).  Faster vibrations give us Ultraviolet, X-rays, and Gamma Rays.  Slower vibrations give us Infrared, Microwave, and Radio waves.

A. What is the relationship between frequency and wavelength?

Q. There is a direct relationship between frequency and wavelength.  This relationship is based on the fact that light travels at a constant speed of 299,792,458 meters per second.

wavelength = speed of light divided by frequency. The speed of light is represented by "c",  frequency by "f", and wavelength by the Greek lambda.

All content copyright 2006 - 2007, Jim Rienhardt d/b/a/ Museum of Light and Sound