18.1 electromagnetic waves opener #4 - wednesday, march 10, 2010 complete the following questions...

18.1 Electromagnetic Waves

Opener #4 - Wednesday, March 10, 2010Complete 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.


The waves that carry this girl’s cell phone conversation are not visible.

Can a cell phone damage your brain?


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.

Copyright © by Holt, Rinehart and Winston. All rights reserved.

ResourcesChapter menu

Electromagnetic Waves

Section 1 Types of WavesChapter 14

Click below to watch the Visual Concept.

Visual Concept

http://my.hrw.com/sh/hk6_0030390966/student/ch14/sec01/vc01/hk614_01_v01fs.htm





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.



How They Are ProducedElectromagnetic 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.



Electromagnetic waves are transverse waves because the fields are at right angles to the direction in which the wave travels.



How They TravelChanging 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.



The Speed of LightSince 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

➜➜

http://www.pbs.org/wgbh/nova/einstein/hotsciencelight/ligh-flash.html

http://www.pbs.org/wgbh/nova/physics/speed-light.html


What is the dual nature of electromagnetic radiation?

Wave or Particle?


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 cameoff the internet.

TRY THIS AT HOME!!!!

QuickTime™ and a decompressor

are needed to see this picture.


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/mythbusters-house-popcorn/

NOTE VIDEO #2 EXPLAINS. FIRST VIDEO IS ALSO INTERESTING BUT NOT REQUIRED TO WATCH...





The Dual Nature of Light

Section 1 The Nature of LightChapter 18


Visual Concepthttp://my.hrw.com/sh/hk6_0030390966/student/ch15/sec02/vc00/hk615_02_v00fs.htm




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 believeeverything you seeon the internet!!!! Your brain would fry or catch your hair on fire!


Evidence for the Wave ModelA 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?


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.


Evidence for the Particle ModelWhen 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?

QuickTime™ and aYUV420 codec decompressor


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

http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/chapter7/medialib/0707.html


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?



Energy of a Photon

Section 1 The Nature of LightChapter 18


Visual Concepthttp://my.hrw.com/sh/hk6_0030390966/student/ch15/sec02/vc01/hk615_02_v01fs.htm




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?

QuickTime™ and a decompressor


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...--->


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


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


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


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.


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



2. What is the wavelength of a radio wave that has a frequency of 1.5 x 106 Hz? (c = 3.0x108 m/s because electromagnetic waves travel at constant speed or velocity in a vacuum unlike mechanical waves.)a. 45 mb. 200 mc. 450 md. 2 km



2. What is the wavelength of a radio wave that has a frequency of 1.5 x 106 Hz? (c = 3.0x108 m/s)a. 45 mb. 200 mc. 450 md. 2 km

ANS: B (v = f x wavelength, so wavelength = v/f

wavelength = 3.0x108/1.5 x 106 = 2 x 102 m = 200 m



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.



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



1. As photons travel farther from a light source, the intensity of light stays the same.

TrueFalse



1. As photons travel farther from a light source, the intensity of light stays the same.

TrueFalse

ANS: F, decreases


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.

18.1 electromagnetic waves opener #4 - wednesday, march 10, 2010 complete the following questions...

Documents

electromagnetic waves

electromagnetic waves

mechanical waves

transverse waves

electromagnetic radiation

types of waves chapter

changing electric fields

changing magnetic fields