# 18.1 Electromagnetic Waves Opener #4 - Wednesday, March 10, 2010 Complete the following questions using complete sentences. Section 17.3 assessment pg.

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18.1 Electromagnetic Waves Opener #4 - Wednesday, March 10, 2010 Complete the following questions using complete sentences. Section 17.3 assessment pg. 512 #1-5. CW: Notes 18.1 and 18.4. CW: Light and mirror lab investigations... HW: ch.17-18-19 assessment questions due Friday... (see end of 18.4 notes to record...) Test ch. 17-18-19 will be on Monday now.... but will be open book. You will want to make an outline of content along with formulas and use of notes to help you.

18.1 Electromagnetic Waves The waves that carry this girl’s cell phone conversation are not visible. Can a cell phone damage your brain?

18.1 Electromagnetic Waves How are electromagnetic waves different from mechanical waves? What Are Electromagnetic Waves? Electromagnetic waves are produced when an electric charge vibrates or accelerates. Electromagnetic waves can travel through a vacuum, or empty space, as well as through matter.

18.1 Electromagnetic Waves Electromagnetic waves are transverse waves consisting of changing electric fields and changing magnetic fields. Like mechanical waves, electromagnetic waves carry energy from place to place. Electromagnetic waves differ from mechanical waves in how they are produced and how they travel. What Are Electromagnetic Waves?

18.1 Electromagnetic Waves How They Are Produced Electromagnetic waves are produced by constantly changing electric fields and magnetic fields. An electric field in a region of space exerts electric forces on charged particles. Electric fields are produced by electrically charged particles and by changing magnetic fields. A magnetic field in a region of space produces magnetic forces. Magnetic fields are produced by magnets, by changing electric fields, and by vibrating charges. What Are Electromagnetic Waves?

18.1 Electromagnetic Waves Electromagnetic waves are transverse waves because the fields are at right angles to the direction in which the wave travels. What Are Electromagnetic Waves?

18.1 Electromagnetic Waves How They Travel Changing electric fields produce changing magnetic fields, and changing magnetic fields produce changing electric fields, so the fields regenerate each other. Electromagnetic waves do not need a medium. The transfer of energy by electromagnetic waves traveling through matter or across space is called electromagnetic radiation. What Are Electromagnetic Waves?

18.1 Electromagnetic Waves The Speed of Light Since Michelson, many other scientists have measured the speed of light. All electromagnetic waves travel at the same speed when in a vacuum, regardless of the observer’s motion. The Speed of Electromagnetic Waves old link: http://www.pbs.org/wgbh/nova/einstein/hotsciencelight/ligh-flash.html Click below on the link for the interactive question on which object slows down light the most? SELECT “LAUNCH INTERACTIVE” NEXT TO KITCHEN PICTURE ITEMS. Click on the item you think is correct. Once you find the correct answer, return... READ EACH ONE. http://www.pbs.org/wgbh/nova/physics/speed-light.html ➜ ➜

18.1 Electromagnetic Waves What is the dual nature of electromagnetic radiation? Wave or Particle?

18.1 Electromagnetic Waves Scientists know that electromagnetic radiation travels as a wave. Scientists also have evidence that electromagnetic radiation behaves like a stream of particles. So which is light, wave or particle? It is both. Wave or Particle? OK - REMEMBER THE CELL PHONE QUESTION. WATCH THIS AND TELL ME WHAT YOU THINK. It came off the internet. TRY THIS AT HOME!!!!

18.1 Electromagnetic Waves The fact that light casts a shadow has been used as evidence for both the wave model of light and the particle model of light. Wave or Particle? TRYING THE POPCORN AND CELL PHONE EXPERIMENT. PERHAPS, YOU SHOULD CLICK THIS VIDEO LINK http://dsc.discovery.com/videos/mythbuster s-house-popcorn/ NOTE VIDEO #2 EXPLAINS. FIRST VIDEO IS ALSO INTERESTING BUT NOT REQUIRED TO WATCH...

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Dual Nature of Light Section 1 The Nature of Light Chapter 18 Click below to watch the Visual Concept. Visual Concept http://my.hrw.com/sh/hk6_0030390966/student/ch15/sec0 2/vc00/hk615_02_v00fs.htm

18.1 Electromagnetic Waves When light passes through a single slit and then a double slit, it produces an interference pattern. Wave or Particle? Light source Card with one slit Card with two slits Interference pattern appears on screen. Light from single slit produces coherent light at second card. Bright bands show constructive interference. Dark bands show destructive interference. April fools LATE! GOT - YOU! Don’t believe everything you see on the internet!!!! Your brain would fry or catch your hair on fire!

18.1 Electromagnetic Waves Evidence for the Wave Model A beam of light passes first through a single slit and then through a double slit. Where light from the two slits reaches a darkened screen, there are alternating bright and dark bands. The bands are evidence that the light produces an interference pattern. Interference occurs only when two or more waves overlap. Wave or Particle?

18.1 Electromagnetic Waves A. Red light or infrared rays, no matter how bright, does not cause electrons to be emitted from this metal surface. B. When blue light or ultraviolet rays strike the metal surface, electrons are emitted, even if the light is dim. Wave or Particle? Bright red light or infrared rays Metal plate Dim blue light or ultraviolet rays Metal plate No electrons are emitted. Electrons are emitted.

18.1 Electromagnetic Waves Evidence for the Particle Model When dim blue light hits the surface of a metal such as cesium, an electron is emitted. A brighter blue light causes even more electrons to be emitted. Red light, no matter how bright it is, does not cause the emission of any electrons from this particular metal. Wave or Particle? Watch the meter... It goes down to zero when red is placed between the light source.

Photoelectric Effect When blue light is shone on the emitter plate, a current flows in the circuit

Photoelectric Effect (cont’d) But for red light, no current flows in the circuit video clip

18.1 Electromagnetic Waves The emission of electrons from a metal caused by light striking the metal is called the photoelectric effect. In 1905, Albert Einstein (1879–1955) proposed that light, and all electromagnetic radiation, consists of packets of energy. These packets of electromagnetic energy are now called photons. Wave or Particle?

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy of a Photon Section 1 The Nature of Light Chapter 18 Click below to watch the Visual Concept. Visual Concept http://my.hrw.com/sh/hk6_0030390966/student/ch1 5/sec02/vc01/hk615_02_v01fs.htm

18.1 Electromagnetic Waves Each photon’s energy is proportional to the frequency of the light. Blue light has a higher frequency than red light, so photons of blue light have more energy than photons of red light. Wave or Particle? Blue light consists of photons that have enough energy to cause electrons to be emitted from a metal surface. Red light photons have too little energy to cause any electrons to be emitted from a metal surface. Watch blue light effect...--->

18.1 Electromagnetic Waves The closer you are to a source of light, the brighter the light appears. Photons travel outward from a light source in all directions. Near the light source, the photons spread through a small area, so the light is intense. Farther from the source, the photons spread over a larger area. Intensity

18.1 Electromagnetic Waves Intensity is the rate at which a wave’s energy flows through a given unit of area. A wave model also explains how intensity decreases. As waves travel away from the source, they pass through a larger and larger area. The total energy does not change, so the wave’s intensity decreases. Intensity

18.1 Electromagnetic Waves The closer you are to a surface when you spray paint it, the smaller the area the paint covers, and the more intense the paint color looks. Intensity

18.1 Electromagnetic Waves Assessment Questions - Be sure to read through these... 1. How are electromagnetic waves different from all mechanical waves? a. Electromagnetic waves don’t carry energy. b. Electromagnetic waves are invisible. c. Electromagnetic waves are longitudinal waves. d. Electromagnetic waves can travel through a vacuum.

18.1 Electromagnetic Waves Assessment Questions 1. How are electromagnetic waves different from all mechanical waves? a. Electromagnetic waves don’t carry energy. b. Electromagnetic waves are invisible. c. Electromagnetic waves are longitudinal waves. d. Electromagnetic waves can travel through a vacuum. ANS:D

18.1 Electromagnetic Waves Assessment Questions 2. What is the wavelength of a radio wave that has a frequency of 1.5 x 10 6 Hz? (c = 3.0x10 8 m/s because electromagnetic waves travel at constant speed or velocity in a vacuum unlike mechanical waves.) a. 45 m b. 200 m c. 450 m d. 2 km

18.1 Electromagnetic Waves Assessment Questions 2. What is the wavelength of a radio wave that has a frequency of 1.5 x 10 6 Hz? (c = 3.0x10 8 m/s) a. 45 m b. 200 m c. 450 m d. 2 km ANS:B (v = f x wavelength, so wavelength = v/f wavelength = 3.0x10 8 /1.5 x 10 6 = 2 x 10 2 m = 200 m

18.1 Electromagnetic Waves Assessment Questions 3. The photoelectric effect is evidence that light behaves like a. a wave. b. a particle. c. both a wave and a particle. d. neither a wave nor a particle.

18.1 Electromagnetic Waves Assessment Questions 3. The photoelectric effect is evidence that light behaves like a. a wave. b. a particle. c. both a wave and a particle. d. neither a wave nor a particle. ANS:B

18.1 Electromagnetic Waves Assessment Questions 1. As photons travel farther from a light source, the intensity of light stays the same. True False

18.1 Electromagnetic Waves Assessment Questions 1. As photons travel farther from a light source, the intensity of light stays the same. True False ANS:F, decreases

18.1 Electromagnetic Waves Continue with Notes 18.4 before proceeding with light and mirror labs.... When the lab is completed, work on the homework assignment which is due on Friday. The completed lab must be turned in no later than Friday as well. Test on ch. 17-18-19 will be on Monday. Part 1 will probably count on this 9 weeks and part 2 will most likely count on 4th 9 weeks.

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