Light - Electromagnetic Spectrum

Question 1

electromagnetic spectrum

Answer 1

• Visible light has wavelengths between 400 – 700 nm, but electromagnetic waves can have wavelengths shorter or longer than that. Our eyes can’t detect this “light,” but it is fundamentally no different than visible light: it’s an electromagnetic (EM) wave, traveling at c, with a wavelength that our eyes simply aren’t capable of detecting.
• The wavelength of an electromagnetic wave can be anything, from km to smaller than an atom. When the different wavelengths of light are arranged from long to short (or vice versa), the result is called the “Electromagnetic Spectrum.” The Visible Spectrum we discussed in the previous unit is but one section of the overall Electromagnetic Spectrum.
• The EM spectrum is split, somewhat arbitrarily, into a number of regions, depending on how those waves are used. The boundaries of each region are only approximate. NOTE: The ranges given here are somewhat different (and more accurate) than what was on the slides in the video.

Question 2

radio waves

Answer 2

• The longest EM waves, those with wavelengths longer than about 10 cm, are called Radio Waves. As you might guess, they are used to transmit radio signals, as well as over-the-air TV and other communications. They are also useful for astronomers, who study the heavens with huge “radio telescopes.”

Question 3

microwaves

Answer 3

• Microwaves have wavelengths ranging from about 1 micrometer to 10 cm. Guess what? They are used in microwave ovens! They are also used extensively for wireless communications, such as cell phones and satellite TV.

Question 4

infrared

Answer 4

• The word “infrared” means “below red,” because it is the range of EM waves whose frequency and energy is just below red on the spectrum. They range in wavelength from about 700 nm (the red edge of the visible spectrum) to about 1 micrometer. Infrared light is given off by warm objects, like animals. It is also used in TV remotes.

Question 5

visible light

Answer 5

• Visible light ranges from about 400 nm (violet) to about 700 nm (red). It is used for, um, seeing stuff…

Question 6

ultraviolet

Answer 6

• The word “ultraviolet” means “above violet,” because it is the range of EM waves whose frequency and energy lies above violet on the spectrum. UV ranges in wavelength from about 10 nm – 400 nm. UV light from the Sun causes people to tan. It is also energetic enough to cause damage to DNA in skin cells, leading to skin cancer.

Question 7

x-rays

Answer 7

• X-Rays are highly energetic EM waves, with wavelengths from about 0.1 nm to 10 nm. They are energetic enough to pass right through a human body, revealing the bone structure inside. Their energy can also damage cells through a body, leading to cancer.

Question 8

gamma rays

Answer 8

• Gamma Rays are the most energetic EM waves, with wavelengths below 0.1 nm. They are created in highly energetic reactions, such as nuclear fission or during a supernova. They are very dangerous for humans.