Electromagnetic Spectrum

Transcription

1 Lesson 2 Electromagnetic Spectrum visible ultraviolet x-rays gamma-rays frequency wavelength electromagnetic spectrum radio microwaves infrared Vocabulary Source: < (continued) Measuring the Electromagnetic Spectrum You actually know more about it than you may think! The electromagnetic (EM) spectrum is just a name that scientists give a bunch of types of radiation when they want to talk about them as a group Radiation is energy that travels and spreads out as it goes-visib a light that comes from a lamp in your house or radio waves that come from a radio station are two types of electromagnetic radiation. Other examples of EM radiation are microwaves, infrared and ultraviolet light, x-rays, and gamma-ras. Hotter, more energetic objects and events create higher energy radiation than cool objects. Only extremely hot objects or particles moving at very high velocities can create higher energy radiation than cool objects. Only extremely hot objects or particles moving at very high velocities can create highenergy radiation like x-rays and gamma-rays. Electromagnetic Spectrum* Learning Outcomes After completing this lesson you will be able to compare and contrast various types of electromagnetic radiation with respect to relative energy, frequency, wavelength, and human perception provide examples of technologies that use electromagnetic radiation, and describe potential positive and negative impacts of their uses Grade 8 Science Module 4, Lesson 2 15

2 Itiv^ b u1 V\ 16 Module 4, Lesson 2 Grade 8 Science Here are the different types of radiation in the EM spectrum, in order from the lowest energy to the highest: Long Wavelength Low Frequency Low Energy Electromagnetic Spectrum Radio Microwave Infrared Visible Ultra Violet Light ea/// I `\\,r o Short Wavelength High Frequency High Energy X-Ray Gamma Rays Radio: Yes, this is the same kind of energy that radio stations emit into the air for your boom box to capture and turn into your favorite Mozart, Madonna, or Coolio tunes. But radio waves are also emitted by other things... such as stars and gases in space. You may not be able to dance to what these objects emit, but you can use it to learn what they are made of. Microwaves: They will cook your popcorn in just a few minutes! In space, microwaves are used by astronomers to learn about the structure of nearby galaxies, including our own Milky Way! Infrared: We often think of this as being the same thing as "heat,' because it makes our skin feel warm. In space, IR light maps the dust between stars. Visible: Yes, this is the part that our eyes see. Visible rad i a t oi is emitted by everything from fireflies to light bulbs to stars... also by fast-moving particles hitting other particles. Ultraviolet: We know that the sure is a source of ultraviolet (or UV) radiation, because it is the UV rays that cause our skin to burn! Stars and other "hot" objects in space emit UV radiation. (continued) - ` a

3 /5 Y ^e^,^ca( G^,scae^cdt. _ Grade 8 Science Module 4, Lesson 2 17 A Radio Wave is not a Gamma-Ray, a Microwave is not an X-ray... or is it? We may think that radio waves are completely different physical objects or events than gamma-rays. They are produced in very different ways, and we detect them in different ways, but are they really different things? The answer is "no". Radio waves, visible light, x-rays, and all the other parts of the electromagnetic spectrum are fundamentally the same thing. They _ ar a all electromanetic_ radiation. Electromagnetic radiation can be described in terms of a stream of photons, which are massless particles each traveling in a wave-like pattern and moving at the speed of light. Each photon contains a certain amount (or bundle) of energy, and all electromagnetic radiation consists of these photons. The only difference between the various types of electron netic radiation is the amount of enemy found in the photons. Radio waves have photons with low energies, microwaves have a little more energy than radio waves, infrared has still more, then visible, ultraviolet, X-rays, and... the most energetic of all... gamma-rays. Actually, the electromagnetic spectrum can be expressed in terms of energy, wavelength, or frequency. Each way of thinking about the EM spectrum is related to the others in a precise mathematical way. Frequency is measured in cycles per second (which is called a Hertz), wavelength is measured in meters, and energy is measured in electron volts. Scientists use whatever units are easiest for whatever they are working with. Gamma-rays: Radioactive materials (some natural and others made by in things like nuclear power plants) can emit gamma-rays. Big particle accelerators that scientists use to help them understand what matter is made of can sometimes generate gamma-rays. But the biggest gamma-ray generator of all is the universe! It makes gamma radiation in all kinds of ways. XXrays: Your doctor uses them to look at your bones and your dentist to look at your teeth. Hot gases in the universe also emit-x-rays.

4 18 Module 4, Lesson 2 Measuring Wavelengths Electromagnetic radiation ation describes a stream of massless particles, each travelling, in a wave-like pattern at the speed of light, and containing a certain amount of energy. The electromagnetic spectrum is the term used to describe the whole range of different tykes of electrom etic radiation, each with its own wavelength, frequency, and amount of energy. Types of electromagnetic radiation include: radio waves microwaves, infrared radiation, visible light, ultraviolet radiation, X-ra s and gamma-rays. Questions: Waves 1. Electromagnetic radiation also moves in waves. To find the wavelen hs of the representative diagram below, use a ruler to measure the distance from one crest to another. trough trough What is the measurement of each wavelength above?.42 cm 2. The number of waves within a specified distance is the frequency of a wave of electromagnetic radiation. Part 1: Using a ruler, determine the wavelength of each sample. Part 2: Identify the number of waves per sample. Part 3: Identify which has the highest (most waves per cm) frequency. a. b. c. Part 1: Wavelength (cm) ^s 3 Grade 8 Science Part 2: Frequency Part 3: Identify Highest Frequency ^

5 Grade 8 Science Module 4, Lesson 2 19 v v ci /I Of 1^4a.C_L G^ E'G 1. What is the relationship of the red wavelength to the green? 9. Which colour has the lowest frequency? Ped 8. Which colour has the highest frequency? VIO l e, 7. Which colour has the longest wavelength? t8 6. Which colour has the shortest wavelength? V 2. Types of radiation found near the left end of the spectrum have low energy, and so also have /d w frequency and Q wavelength. low/high sho ong 3. Types of radiation found near the right end of t)e spectrum have high energy, and so also have _AI `i low 'gh frequency and t wavelength. short/long 4. Which have more energy: a. gamma rays or radio waves? aiv a b. ultraviolet rays or x-rays? --/a S c. infrared rays or ultraviolet rays? nl 1/iCi d. visible light or radio waves? J/l S'i 5. Which is the only form of energy we can see? //k e Refer back to the information and the diagram of the electromagnetic spectrum to answer the following questions. 1. The electromagnetic spectrum is made up of radiation, or e-/1 y that travels and spreads out as it goes. Questions: The Electromagnetic Spectrum 3. What is the relationship between the wavelength and the frequency of a wave of electromagnetic radiation? 5 4C/ /oz L res

6 2 Module 4, Lesson 2 The Electromagnetic Spectrum and Its Uses Different parts of the electromagnetic spectrum have been put to different uses. Some of these are described below: Radio Waves: radio, television, and CB radio broadcasting; radar Microwaves: communications, cooking Grade 8 Science 13. True or False a. Radiation is energy that travels and spreads out as it goes. b. Electromagnetic radiation is a stream of photons, each containing a certain amount of energy. c. Hotter, more energetic objects create lower energy radiation than cool objects. T d. Stars emit radio waves. --- e. Stars do not emit UV radiation. f. Radio waves and gamma-rays are completely different things. g. Infrared rays are often thought of as heat rays. h. The sun gives off ultraviolet and infrared energy. 7^..^..+i. Visible light is part of the electromagnetic spectrum. T j. Visible light takes up only a small part of the electromagnetic spectrum. k. We can see ultraviolet light. 1. We can see infrared light. ti' LL!^ G Gr cr' C Cif 11. What is the relationship of the red frequency to the green? Reif a, P a ci elm /^e! 12. Fiom our Y answers tli P revious q uestions name e relationship between wavelength and frequency.

7 Grade 8 Science Module 4, Lesson 2 21 While there are many important uses for the various types of electromagnetic radiation, there are also some dangers associated with them. At one time or another, you have probably had a sunburn. Ultraviolet light is needed by humans, but only in small doses. Too much can damage the skin. Overexposure to ultraviolet radiation can be so damaging to skin cells that it can cause skin cancer. Even x-rays have some potentially harmful side effects. At one time, small x-ray machines could be found in shoe stores to help people ensure their shoes fit properly. Eventually scientists realized that too much exposure to this type of radiation could cause serious damage to humans. If you have an x-ray today, you'll find that it is done very carefully with shielding used to help protect the parts of your body that are not being examined. Infrared Light: sensors in satellites and airplanes can give important information on the health of crops and can help us see forest fires even when there is a blanket of smoke Ultraviolet Light: suntan lamps, destroying germs, special lighting effects X- Rays: medical examinations, treating diseases, ins^ectin metals for defects Gamma-Rays: treating cancer, medical research, providing information on the life and death of stars in our universe

8 22 Module 4, Lesson 2 Grade 8 Science Notes