Since the time of the Greek philosophers in the 5th century BC, mankind has speculated about the nature of light. Today, physicists have learned through experimentation that light has a dual nature and behaves as a particle at times and as a wave at other times. Light particles are called photons and are different from particles of matter because they have no mass and always move at a constant speed of nearly 299,792 kilometers per second, or 186,281 miles per second through empty space. This makes light the fastest phenomenon known in the universe. Yet light is also a form of radiant energy, or energy that travels in waves, which only slows down when inside substances such as air, water, glass, or diamond.
In this activity, our photon was traveling in a single frequency or wavelength. Most often, however, light of many frequencies or even all frequencies travels toward the surface of objects. When this occurs, objects have a tendency to selectively absorb, reflect or transmit certain frequencies from the light. For example, one object might reflect red light while absorbing all other frequencies (colors) of visible light. The manner in which visible light interacts with an object is dependent upon the frequency of the light and the nature of the atoms of the object. The electrons of atoms have a natural frequency at which they tend to vibrate. If a light wave of a given frequency strikes a material with electrons having the same vibrational frequencies, then those electrons will absorb the energy of the light wave. Otherwise, they will reflect or transmit it.
Students learn in this activity that when light shines on an object, it is reflected, absorbed, or transmitted through the object, depending on the object’s material and the frequency (color) of the light. However, not all frequencies of energy found within the electromagnetic spectrum are reflected, absorbed, or transmitted similarly. Have students watch the NASA video on YouTube (or download it ahead of time), "More than Your Eyes Can See." Have students explore the behavior of other types of energy: x-rays, gamma rays, ultraviolet waves... as a precursor for more in-depth exploration of the electromagnetic spectrum.