The Electromagnetic Spectrum Notes

What Is An Electromagnetic Wave? An electromagnetic (EM) wave consists of vibrating electric and magnetic fields that move through space at the speed of light. An EM wave is a transverse wave that carries electrical and magnetic energy. The energy is EM radiation. Light is an example of and EM wave.

What Is An Electromagnetic Wave? EM waves do not need a medium to travel through. They can travel though empty space (vacuum). For example, sunlight travels through empty space to reach Earth. Light and all other EM waves are produced by charged particles. Charged particles have an electric field surrounding them. When a charged particle moves, it produces a magnetic field. Thus, a moving charged particle is both electric AND magnetic.

What Is An Electromagnetic Wave? All EM waves travel at the same speed. In a vacuum, they travel at about 300,000 km/s or 186,000 miles/s. This is known as the speed of light. At this speed, light from the sun takes 8.3 minutes to travel the 150 million kilometers to Earth.

What is the EM Spectrum? All EM waves travel at the same speed in a vacuum, but they have different wavelengths (λ) and different frequencies (f). The EM spectrum is made up of radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV) light, X-rays, and gamma rays. The EM spectrum is the complete range of EM waves. The waves are placed in order of increasing f. As the frequencies of the waves get higher, their λ get shorter.

What is the EM Spectrum? At one end of the EM spectrum are radio waves. Radio waves have low frequencies and long wavelengths. At the other end of the spectrum are gamma rays. Gamma rays have high f and short λ. The higher the frequency of the EM waves, the more energy they have. The farther up the spectrum you go, the more harmful the waves become to humans. Gamma waves have the highest frequency, so they have the most energy, and therefore cause the most harm to humans.

Radio Waves Radio waves are at one end of the EM spectrum. Radio waves are EM waves with the lowest frequencies and longest wavelengths. Radio waves with the very lowest f are used to carry signals for radio and TV programs.

Infrared Infrared rays follow radio waves in the EM spectrum. Infra- is a prefix meaning “before” or “below.” So infrared means “below red.” Infrared (IR) rays are EM waves with higher frequencies and shorter wavelengths than radio waves. IR rays have more energy than radio waves because they have higher f. You can feel the energy of IR rays as heat. heat lamps give off infrared rays.

Infrared Most objects give off some IR rays. You can use an infrared camera to see objects in the dark. These cameras take pictures called thermograms.

Visible Light Visible light follows infrared rays in the EM spectrum. EM waves that you can see are called visible light. Visible light has higher f and shorter λ than infrared rays. All colors of light visible have wavelengths that fall between 390 nm (3.9x10-7 m) and 750 nm (7.5x10-7m). Anything with wavelengths outside of this range, humans beings cannot see directly.

Visible Light We see different wavelengths of visible light as different colors. When all colors combine, we see white light. A prism has the ability to diffract white light into its seven parts. From shortest to longest λ, the colors of visible light are ROY G BIV. Red Orange Yellow Green Blue Indigo Violet

Ultraviolet Rays Ultraviolet (UV) rays follow visible light in the EM spectrum. UV rays are EM waves with higher frequencies and shorter wavelengths than visible light. UV rays have more energy than visible light because they have higher frequencies. UV rays help our bodies make vitamin D. However, too much UV radiation can cause sunburn, damage your eyes, and cause skin cancer.

X-Rays X-rays follow UV rays in the EM spectrum. X-rays are EM waves with higher frequencies and shorter wavelengths than UV rays. X-rays have more energy than UV rays because they have higher f. X-rays have enough energy to pass through many materials, including skin and other soft tissues. Even though X-rays are used to take pictures of teeth and bones, and - in engineering - industrial materials, too much exposure can cause serious health issues including cancer.

Gamma Rays Gamma rays follow X-rays in the EM spectrum. Gamma rays are EM waves with the highest frequencies and shortest wavelengths. Gamma rays have more energy than any other type of EM wave. Gamma rays have enough energy to pass through most materials. Some gamma rays can be used to kill cancer, or to examine internal structures of the body. Some objects in space give off gamma rays. Special telescopes can detect these gamma rays.

Types of Telescope Telescopes are instruments that collect and focus light and other forms of EM radiation. A telescope that collects and focuses visible light is called an optical telescope. The two major types of optical telescopes are refracting telescopes and reflecting telescopes.

Types of Telescopes A radio telescope is a device used to collect radio waves that come from objects is space. Most radio telescopes have large, curved surfaces like dishes. Radio telescopes can combine multiple dishes to form one larger dish.

The Very Large Array (VLA) in New Mexico is a set of 27 radio telescopes that can be maneuvered and combine together to form one radio telescope 25 kilometers in diameter. The Arecibo radio telescope in Puerto Rico was built into a natural bowl in the ground. It is 305 meters in diameter and is the largest single radio telescope in existence.

Types of Telescopes Telescopes have also been developed to look at all parts of the EM spectrum. Telescopes can now see into the infrared, microwave, X-ray, ultraviolet, and Gamma rays of the EM spectrum.