2. 18.2 The Electromagnetic Spectrum

3. Finding the Electromagnetic Spectrum Today, we know that we can’t see certain electromagnetic waves. But how did we discover these waves that we can’t see? http://i.ehow.com/images/GlobalPhoto/Articles/5034726/201829-main_Full.jpg

4. Finding the Electromagnetic Spectrum Before the 1800s, nobody knew about electromagnetic waves besides the light that humans could see. At that time, we knew that we could split white light into different colors with a prism. When white light is split, it forms ROY G BIV.

5. Finding the Electromagnetic Spectrum Then, in 1800, William Hershel used a prism and thermometer in an interesting way. Hershel used the prism to split the white light into its colors. Then, he used a thermometer to measure the temperature of each color.

6. Finding the Electromagnetic Spectrum Hershel observed that different colors had different temperatures. The blue end of the colors had a lower temperature than the red end of the colors. This discovery made Hershel wonder what would happen to the temperature beyond the red end of the colors.

7. Finding the Electromagnetic Spectrum He measured the temperature just beyond the red color and found the temperature was even higher than the red area. Hershel concluded there must be invisible radiation beyond the red end of light! This was the beginning of studying invisible types of electromagnetic radiation.

8. The Electromagnetic Spectrum Today, we know that visible light is only a very small amount of frequencies. We can’t see most of the frequencies of electromagnetic waves!

9. The Electromagnetic Spectrum The full range of frequencies of electromagnetic radiation is called the electromagnetic spectrum. It includes: radio waves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays. Each kind of wave is characterized by a range of wavelengths and frequencies.

10. http://ds9.ssl.berkeley.edu/LWS_GEMS/2/images_2/ems510.jpg

11. Our Objectives: To learn about the different parts of the electromagnetic spectrum To find out how each part of the spectrum is useful

12. Radio Waves Radio waves have the longest wavelength (and lowest frequency). Wavelength: 1 mm to +1000 km Frequency: 300,000 megahertz (MHz) or less Uses: Radio, TV, microwaves and radar

13. More About Radio Waves In a radio studio, music and voices are changed into electronic signals that are coded onto radio waves. There are two ways to code and transmit radio waves. They can change the amplitude and keep the frequency the same, or change frequency and keep amplitude the same.

14. More About Radio Waves If we change the amplitude and keep frequency the same, this is called amplitude modulation. This is where we get the term “AM” radio stations. In AM waves, we transmit information by making the waves bigger or smaller.

15. More About Radio Waves If we change the frequency and keep amplitude the same, this is called frequency modulation. This is where we get the term “FM” radio stations. In FM waves, we transmit information by making the waves vibrate faster or slower.

16. More About Radio Waves In the end, your radio decodes the radio waves according to what mode it is in (AM or FM). This is what makes it possible to hear radio stations. AM radio waves: 535 kHz to 1605 kHz FM radio waves: 88 MHz to 108 MHz

17. More About Radio Waves Have you ever “lost” a radio station? This happens when the radio signal becomes too weak to detect. AM waves travel farther than FM waves. Particles in the Earth’s atmosphere reflect the lower- frequency radio waves of AM better than the higher- frequency FM waves.

18. Television Radio waves also carry signals for television. The signals carry information for pictures and sound.

19. Microwaves These waves are still radio waves, and they have the shortest-wavelengths. Wavelengths: 1 meter to 1 millimeter Frequencies: 300 MHz to 300,000 MHz These waves cook and reheat food and carry cell phone conversations.

20. Radar “Radar” is an acronym for radio detection and ranging. (Like Sonar) Radar sends out radio waves and then detect them as they bounce back. This technology uses the Doppler effect to determine how fast an object is moving. The faster the motion, the higher the frequency of the returning radio waves.

21. Infrared Rays Infrared rays have higher frequencies than radio waves and lower frequencies than red light. Wavelength: 1 millimeter to 750 nanometers (1 millionth of a meter) Uses: to heat things and to discover areas of heat differences.

22. Infrared Rays Like radio waves, you cannot see infrared rays. However, unlike radio waves, you can feel them. Your skin senses infrared rays as warmth. The warmer an object is, the more infrared radiation it gives off.

23. Visible Light Then, after radio waves and infrared rays, there is visible light. This is the part of the electromagnetic spectrum that we detect with our eyes. Each color that we see has a particular frequency (and wavelength). Wavelength: 400 nm to 750 nm Frequency: 4.0x10 14 Hz to 7.5x10 14 Hz http://www.windows.ucar.edu/physical_science/magnetism/images/visible_spectrum_waves_big.jpg

24. Ultraviolet Rays (UV) This is the type of radiation that has a higher frequency than violet light. Wavelength: 400 nm to 4 nm Uses: Health, medicine, farming

25. Ultraviolet Rays UV rays help your skin produce vitamin D, which helps the body absorb calcium and produce healthy bones. However, excessive exposure can cause sunburn, wrinkles, skin cancer and damage your eyes. UV rays are used to kill microorganisms and disinfect the air that flows through large buildings. They are also used to help plants grow in the winter.

26. X-Rays These rays have a higher frequency than UV rays (so more energy). They have a high enough energy to be able to penetrate matter that light cannot. Wavelength: 12 nm to 0.005 nm Uses: Medicine, industry, transportation safety

27. X-Rays X-rays are used for looking at your bones. However, too much exposure to X-rays can kill or damage living tissue. Lids of aluminum cans are sometimes inspected with X-rays to make sure they are sealed properly. X-rays are also used to see inside of luggage in an airport.

28. Gamma Rays These have the highest frequencies (and therefore, the most energy). Wavelength: 0.005 nm or less Exposure to tiny amounts of gamma rays are tolerable, but overexposure can be deadly. Uses: Kill cancer cells, make pictures of the brain.