# 17.2 Waves of the electromagnetic Spectrum - PowerPoint PPT Presentation

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17.2 Waves of the electromagnetic Spectrum . Pg. 578 - 585. What is the Electromagnetic Spectrum? . All electromagnetic waves travel at the same speed in a vacuum, BUT they have different wavelengths at different frequencies

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17.2 Waves of the electromagnetic Spectrum

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## 17.2 Waves of the electromagnetic Spectrum

Pg. 578 - 585

### 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

### 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 are the electromagnetic waves with the longest wavelengths and lowest frequencies

• There are two types of Radio Waves:

• 2. Microwaves

• They carry signals for both radio and television programs

• 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

• To measure distance:

• 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