5.4: Types of Electromagnetic Waves

• Electromagnetic waves are classified based on their wavelengths and frequencies
• Electromagnetic waves

  They can be radio waves, microwave, infrared, visible light, ultraviolet, X-ray, and gamma ray. These names are given by scientists based on how humans discovered them, how they affect humans, and how they are used.
• In nature, electromagnetic waves have continuous values of wavelength ranging from very large to very small and there is no clear-cut way to determine which one kind of electromagnetic wave ends and where the other begins.
• The electromagnetic waves with the longest wavelength and lowest frequency are the radio waves.
• Radiowaves


  They have a wavelength just above one meter, and frequencies below 3.0 × 10^8 Hz (cycles per second).
• Microwaves have wavelengths approximately between one m and one mm
• Microwaves


  Their frequencies range from 3.0 × 10^8 - 3.0 × 10^11 Hz in a vacuum
• Waves having shorter wavelengths than microwaves but longer than visible light are called infrared.
• Infrared


  They occupy the wavelength roughly between 1 mm and 700 nm (nm means nanometer, equivalent to 10^-9 m). They are called “infrared” because their frequency is just below that of red light (infra means below).
• Visible light is what our eyes can see
• Visible Light


  They have wavelengths ranging from 700 nm to 400 nm
• The longest wavelength and lowest frequency of visible light is seen as red light while the shortest wavelength and highest frequency is seen as violet light. Arranged in decreasing wavelengths, the order of visible light is red, orange, yellow, green, blue, and violet. However, under certain conditions, humans may be capable of seeing infrared at up to 1050 nm and ultraviolet up to 310 nm.
• Some animals are more sensitive to both higher and lower wavelengths.
• The color of visible light is a continuous spectrum. Their divisions into colors are subjective. Thus, physicists often rely on using the exact wavelength of light in studying them as opposed to colors since the spectrum contains intermediate colors in between divisions.
• Ultraviolet are those with wavelengths usually from 400 nm to 10 nm. They are called “ultraviolet” because their frequency is higher than violet light (ultra means going beyond).
• The electromagnetic waves with the highest amount of energy are X-rays and gamma rays.
• X-rays and Gamma Rays


  They can pass through several opaque materials such as human body tissues
• X-rays


  are those with wavelengths from 10 nm to 100 pm (pm means picometers; 1 pm = 10^-12 m)
• Gamma Rays


  are those with wavelengths less than 100 pm.