In a vacuum, all electromagnetic waves travel at the same speed. But not all electromagnetic waves are the same. Electromagnetic waves vary in wavelength and frequency.
The speed of an electromagnetic wave is the product of its wave-length and its frequency. Because the speed of electromagnetic waves in a vacuum is constant, the wavelength is inversely proportional to the frequency. As the wavelength increases, the frequency decreases. If you know the wavelength of an electromagnetic wave, you can calculate its frequency.
Calculating Wave Speed
A radio station broadcasts a radio wave with a wavelength of 3.0 meters. What is the frequency of the wave?
Read and Understand
What information are you given?
Plan and Solve
What unknown are you trying to calculate?
What formula contains the given quantities and the unknown?
Replace each variable with its known value.
Look Back and Check
Is your answer reasonable?
Check that product of wavelength and frequency gives a speed of 3.0 × 108 m/s.
A global positioning satellite transmits a radio wave with a wavelength of 19 cm. What is the frequency of the radio wave? (Hint: Convert the wavelength to meters before calculating the frequency.)
The radio waves of a particular AM radio station vibrate 680,000 times per second. What is the wavelength of the wave?
Radio waves that vibrate 160,000,000 times per second are used on some train lines for communications. If radio waves that vibrate half as many times per second were used instead, how would the wavelength change?