# 17.2 Waves of the electromagnetic Spectrum

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17.2 Waves of the electromagnetic Spectrum
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What is the Electromagnetic Spectrum?
All electromagnetic waves travel at the same speed in a vacuum, BUT they have different wavelengths at different frequencies Visible Light: Is radiation in the wavelengths that your eyes can see Only a small portion of electromagnetic radiation is visible light The rest of the wavelengths are invisible

Visible Light

What is the Electromagnetic Spectrum?
Recall how speed, wavelength, and frequency are related Speed = Wavelength X Frequency As the wavelength decreases, the frequency increases Waves with the longest wavelength have the lowest frequencies Waves with the shortest wavelength have the highest frequencies **The higher the frequency, the higher its energy

What is the Electromagnetic Spectrum?
The Electromagnetic Spectrum is the complete range electromagnetic waves placed in order of increasing frequency The Order: Radio Waves, Infrared Rays, Visible Light, Ultraviolet Light, X-rays, and Gamma Rays

Radio Waves Radio Waves are the electromagnetic waves with the longest wavelengths and lowest frequencies There are two types of Radio Waves: 1. Broadcast Waves (Radio and TV) 2. Microwaves

A broadcast station sends out radio waves at certain frequencies A radio or TV antenna picks up the waves and converts the radio signals into electrical signals Inside radios the electrical signals are converted into sound Inside TVs the signal is converted into sounds and pictures

Microwaves Microwaves are radio waves with the shortest wavelengths and highest frequencies. Microwaves have many uses Cellular phones, cooking, and radar

Radar is a system that uses reflected radio waves to detect objects and measure their distance and speed

Radar To measure distance: To measure speed:
A radar device sends out radio waves that reflect off an object The time it takes for the reflected waves to return is used to calculate the object’s distance To measure speed: A radar device uses the Doppler effect The difference in frequency is used to calculate the car’s speed

Infrared Rays Infrared Rays are electromagnetic waves with wavelengths shorter than those of radio waves

Heat Lamps Infrared rays have more energy than radio waves
You feel the energy of infrared rays as heat Heat lamps have bulbs that give off mostly infrared rays and very little visible light Heat lamps are used to keep food warm or heat up rooms quickly

Infrared Cameras Most objects give off some infrared rays
Warmer objects give off infrared rays with more energy and higher frequencies Infrared cameras take pictures using infrared rays instead of light These pictures are called thermograms, which is an image that shows regions of different temperatures in different colors Used by firefighters to locate people during fires

Visible Light Visible light are electromagnetic waves that we can see
Visible light has shorter wavelengths and higher frequencies than infrared rays Visible light with the longest wavelength appear red Visible light with the shortest wavelength appear violet in color

Ultraviolet Rays Ultraviolet Rays are electromagnetic waves with wavelengths shorter than those of visible light Ultraviolet Rays have higher frequencies than visible light so they have more energy Have enough energy to damage or kill living cells Ultraviolet lamps are used to kill bacteria on hospital equipment

Ultraviolet Rays and Health
Small doses of ultraviolet rays are useful! Cause skin to produce vitamin D, which is needed for healthy bones and teeth Large doses of ultraviolet rays can be harmful! Can burn your skin, which causes skin cancer and damage to your eyes By applying sun block and wearing sunglasses you can limit the damage caused by ultraviolet rays

X-Rays X-Rays are electromagnetic waves with wavelengths just shorter than those of ultraviolet rays X-Rays have higher frequencies than ultraviolet rays = more energy X-Rays have so much energy they can penetrate most matter except bone Bones absorb X-rays

How X-Rays Work Bones absorb X-rays and does not allow them to pass through X-rays pass through skin and soft tissue, causing the photographic film in the X-ray machine to darken when it is developed Bones absorb the X-rays and appear as the lighter areas on the film

X-Rays Too much X-ray exposure can cause cancer
When X-rays are taken a lead apron is worn during the procedure The lead apron absorbs the X-rays and prevents them from reaching your body

Uses of X-Rays X-rays are sometimes used in industry and engineering
Used to find out if steel has any tiny cracks because the X-rays will pass through the tiny cracks that are not visible to the human eye Used to check the quality of joints in oil and gas pipelines

Gamma Rays Gamma Rays are electromagnetic waves with the shortest wavelengths and highest frequencies Gamma Rays have the most energy Are the most penetrating of all of the electromagnetic waves

Uses of Gamma Rays Radioactive substances and nuclear reactions produce gamma rays Gamma rays are also used in medicine Used to kill cancer cells inside the body Used to examine internal body structures A patient will be injected with fluid that emits gamma rays The gamma ray detector can form an image of the inside of the body

Gamma Rays and Space Some objects in space give off bursts of gamma rays Gamma Rays are blocked by Earth’s atmosphere Gamma ray telescopes that detect the gamma rays must orbit above the Earth’s atmosphere Astronomers believe that explosions of stars in the distant galaxies are one way of producing gamma rays