Slide 1 / 121 New Jersey Center for Teaching and Learning Progressive Science Initiative This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Click to go to website: www.njctl.org Slide 2 / 121 8th Grade Science Unit 6: Electromagnetic Radiation www.njctl.org Slide 3 / 121 Table of Contents Click on the topic to go to that section · What is Electromagnetic Radiation? The Electromagnetic Spectrum · Visible Light · Interactions with · Matter
Slide 4 / 121 What is Electromagnetic Radiation? Return to Table of Contents Slide 5 / 121 Electromagnetic Radiation What do X-rays, light, microwaves, radio waves, and infrared have in common? Slide 6 / 121 Electromagnetic Radiation Radiation can be described as the movement of energy through space. There are many different sources of radiation that vary by intensity. The Sun, light bulbs, nuclear reactions, and radon gas, are all sources that produce electromagnetic radiation.
Slide 7 / 121 Electromagnetic Radiation We are constantly bombarded by electromagnetic radiation, most of which we cannot see. Note http://www.epa.gov/radtown/enter-radtown.html Slide 8 / 121 Electromagnetic Radiation The electromagnetic radiation we interact with is not all bad. When you cook food in a microwave, listen to music, see colors, or feel heat you are experiencing electromagnetic radiation. How does electromagnetic radiation travel through space? Slide 9 / 121 Electromagnetic Radiation One way electromagnetic radiation travels through space is as a wave. Electromagnetic waves are different from mechanical waves because they don't need a medium to travel through. What's "waving" in an electromagnetic wave?
Slide 10 / 121 Electromagnetic Waves Electromagnetic waves are produced by vibrating electric charges. When an electric charge vibrates its electric field changes, producing a changing magnetic field perpendicular to it, the changing magnetic field produces a changing electric field produces a changing magnetic field produces a changing electric field produces a changing magnetic field... creating a transverse electromagnetic wave Slide 11 / 121 How Electromagnetic Waves Travel Electromagnetic waves do not need a medium to travel through. This means electromagnetic waves can travel through anything, such as in air, water, or even mostly empty space! Electromagnetic waves also do not lose energy as they travel unlike mechanical transverse waves which lose some of their energy to their medium. An electromagnetic wave continues to go straight and spread out until it collides with some form of matter, at which point the direction of travel will change. Slide 12 / 121 Electromagnetic Wave Characteristics Electromagnetic waves have the same wave characteristics we studied last unit: wavelength ( ) measured in meters frequency (f) measured in Hz speed (c) 300,000,000 meters/second Wavelength and frequency vary based on the type of electromagnetic wave, but all electromagnetic waves travel at the same speed in a vacuum . What is a vacuum?
Slide 13 / 121 The Vacuum of Empty Space A vacuum is a space that is completely empty, containing no matter. A true vacuum does not actually exist because even nearly empty parts of the Universe contain some matter. The closest thing to a vacuum that has been produced in a lab is a space that has one billionth of one billionth of the standard pressure of the atmosphere! Slide 14 / 121 Speed of Electromagnetic Radiation Scientists use the idea of constant speed (c) in a vacuum because it's useful for calculations. c is also refered to as the speed of light. In theory, nothing can travel faster than the speed of light (maybe?). In reality, any matter an electromagnetic wave encounters will slow it down. If you could travel at the speed of light, you could go around the Earth's equator 7.5 times in one second. Slide 15 / 121 Wavelength of Electromagnetic Radiation Different types of electromagnetic radiation have different wavelengths. A wavelength is the distance between adjacent crests.
Slide 16 / 121 Frequency of Electromagnetic Radiation Since all forms of electromagnetic radiation travel at the same speed when not in contact with matter but have different wavelengths, then different forms of electromagnetic radiation also have different frequencies. There is an inverse relationship (opposite) between wavelength and frequency. The longer the wavelength, the lower the frequency. Slide 17 / 121 Relationship Between Speed, Wavelength, and Frequency A wave's frequency or wavelength can be solved for using the wave equation from last unit: The only difference is that since all electromagnetic radiation travels at the speed of light, then v can be replaced with this value every time, represented by the letter c , which equals 300,000,000 m/s. We use the new wave equation to solve for the frequency or wavelength of electromagnetic waves based on the equations below: or Click here to see how to prove the speed of light using chocolate and a microwave. Slide 18 / 121 1 If you could travel at the speed of electromagnetic waves in a vacuum, how long would it take you to travel from the surface of the Earth to the Moon? speed = c = 300,000,000 m/s distance between Earth and Moon = 356,400 km or 356,400,000 m t = d/s Answer
Slide 19 / 121 2 The Sun is 149,600,000 km away from the Earth. How many minutes ago did the radiation that is hitting you right now leave the Sun? c = 300,000,000 m/s 1000 m = 1 km 60 seconds = 1 min Answer Slide 20 / 121 3 Radio waves are electromagnetic waves with long wavelengths. If an AM radio wave's frequency is 540,000 Hz, what is its wavelength? Is it long enough to bounce over the Empire State Building (381 m)? c = 300,000,000 m/s Answer Slide 21 / 121 4 What is the frequency of a radio wave that has a wavelength of 1 cm (0.01 m)? Answer
Slide 22 / 121 5 An electromagnetic wave has a frequency of 1.5 GHz (1,500,000,000 Hz). What is the wavelength of the wave? Answer Slide 23 / 121 6 Red light has a frequency of 4.6 x 10 14 Hz (460,000,000,000,000 Hz). What is the wavelength of red light? Answer Slide 24 / 121 7 Which of the following electromagnetic wavelengths would have the highest frequency? A 100 m B 10 m Answer C 1 m D 0.1 m
Slide 25 / 121 8 Which of the following frequencies would have the shortest wavelength? A 1000 Hz Answer B 100 Hz C 10 Hz D 1 Hz Slide 26 / 121 Electromagnetic Radiation Electromagnetic radition can also travel through space in packets of energy called photons. In high school physics you'll learn more about how electromagnetic radiation can be both a wave and a particle... Slide 27 / 121 The Electromagnetic Spectrum Return to Table of Contents
Slide 28 / 121 The Electromagnetic Spectrum Electromagnetic radiation is organized by how much energy it carries. The range of electromagnetic radiation is called the Electromagnetic Spectrum. The first 5 minutes of the video provide a perfect introduction to the EM spectrum and review of Note previous concepts. The entire video is 35 minutes long, so you may suggests students watch the rest on their own. Click here to watch a NASA video on the EM Spectrum Slide 29 / 121 The Electromagnetic Spectrum The different types of electromagnetic waves from that make up the spectrum are from left to right: Radio, Microwave, Infrared, Visible Light, Ultraviolet, X-ray and Gamma ray Slide 30 / 121 Energy Differences For Types of Electromagnetic Radiation The higher the frequency, the higher the energy. Which type of electromagnetic radiation has the highest energy?
Slide 31 / 121 9 Which of the following forms of electromagnetic radiation has the longest wavelength? A Microwaves B Radio Waves C Visible Light Answer D X-rays Slide 32 / 121 10 Which of the following forms of electromagnetic radiation has the shortest wavelength? A Gamma Waves B Ultraviolet Answer C Infrared D Visible Light Slide 33 / 121 11 Which of the following forms of electromagnetic radiation has the highest frequency? A Microwaves B Infrared Answer C Ultraviolet D X-ray
Slide 34 / 121 12 Which of the following forms of electromagnetic radiation has the lowest frequency? A Radio Waves Answer B Ultraviolet C X-rays D Gamma rays Slide 35 / 121 13 Which of the following forms of electromagnetic radiation carries the lowest energy? A Visible Light B Infrared Answer C Radio D Microwaves Slide 36 / 121 14 Which of the following forms of electromagnetic radiation carries the highest energy? A Radio Answer B X-ray C Ultraviolet D Infrared
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