Under most conditions, light acts like a wave. According to Maxwell's equations, light is composed of oscillating electric and magnetic fields that pass through a vacuum at a certain constant velocity, c. The electric fields and magnetic fields are perpendicular to each other, and both are perpendicular to the direction of travel (see Figure 2.1). The electric and magnetic fields have specific directions as well as magnitudes, and so are properly thought of as vectors. It is interesting to note that two aspects of light have particle-like behavior: its energy (a fact deduced by Max Planck) and its momentum (first observed by Arthur Compton in 1923).
Like anything that acts as a wave, the behavior of light can be described by mathematical equations.
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