The speed of an electromagnetic wave is 3×108 m/s in a vacuum, and the energy of a wave can be calculated using the equation E=hf. Light travels slower in an optically dense medium than in a vacuum because the light is absorbed and then re-emitted by the medium itself.
The frequency determines the type of EM wave. The higher the frequency, the higher the energy. This can be calculated by using the equation E = hf where h = 6.62607015×10−34 J⋅s. is Planck’s constant.
Wavelength is the distance travelled for an EM wave to complete one cycle. As speed is constant in the same medium, frequency changes will cause wavelength changes. The wavelength λ can be used to calculate the wave speed C using the frequency f. And frequency can be calculated by using one over the wavelength to calculate the frequency in Hz.
C = fλ
F = 1/λ
Electromagnetic waves are transverse waves, which oscillate up and down, perpendicular to the direction of propagation whereas sound waves are longitudinal waves, waves which the displacement of the medium is in the same direction as, or the opposite direction to, the direction of propagation of the wave.
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Key Points
• Velocity equals constant c = 3×10^8 in a vacuum.
• Electromagnetic radiation consists of perpendicularly oscillating electric and magnetic fields; the direction of propagation is perpendicular to both.
Key Terms
Planck’s constant: h = 6.62607015×10−34 J⋅s.
Transverse wave: oscillates up and down, perpendicular to the direction of propagation.
Longitudinal waves: waves in which the displacement of the medium is in the direction of propagation of the wave
Wavelength: the distance travelled for an EM wave to complete one cycle.