Electromagnetic Waves

Electromagnetic waves consists of of oscillations in electric and magnetic fields that can travel through space.  Visible light, x-rays, and radio waves are all forms of electromagnetic radiation.   Unlike the more familiar sound waves, electromagnetic waves do not require a medium for their propagation.

Electromagnetic radiation can be described by three properties, which are

• energy
• wavelength
• frequency

The wavelength is the distance between any two identical points in consecutive cycles.  Wavelength is denoted by the Greek letter  (lambda).  A common SI unit of wavelength is the nanometer( 1 nm = 10^-9m).

The frequency of a wave is the number of cycles or wavelengths that pass by a point in a unit of time.  Frequency is denoted by the Greek letter (nu).  The SI unit of frequency is the hertz (Hz).  A hertz is one cycle or wavelength per second. ( 1 Hz = 1 s^-1)

Wavelength and frequency are inversely related, the greater the wavelength, the lower the frequency, and vice versa.  The product  · is the total length of the wave that has passed a point in one second and is therefore a speed.  The speed of electromagnetic waves in a vacuum is denoted by the letter c.  The equation relating wavelength and frequency is  c =   · 

The types of electromagnetic radiation range from short-wavelength, high-frequency gamma rays to long-wavelength, low-frequency radio waves.  This range of wavelengths and frequencies is known as the electromagnetic spectrum, and is shown below.

 The energy of a unit of electromagnetic radiation is directly proportional to the frequency and inversely proportional to the wavelength.  The energy is given by the expression, E = , where is the frequency and h is a constant called Planck's constant with a value of