Chapter 18 The Electromagnetic Spectrum and Light

Transcription

1 Chapter 18 Sections 18.1 Electromagnetic Waves 18.2 The 18.3 Behavior of Light 18.4 Color 18.5 Sources of Light Chapter 18 The and Light Section 18.1 Electromagnetic Waves To review: mechanical waves require Examples of mechanical waves include Sound waves are waves Electromagnetic Waves Electromagnetic waves are waves EM waves do not need a Can travel through EM waves are made by Instead of transferring energy from particle to particle, EM waves travel by transferring energy between Magnetic Fields EM waves are produced by constantly changing electric and magnetic fields Magnetic fields the area around a magnet Magnetic fields are created by Electric Fields Electric Field the area around an electric charge in which it can Electric fields are created by and by Relationship Between Electric-Fields and Magnetic Fields Demonstration of the relationship between electric and magnetic fields Describe Demo: A changing magnetic field creates a The reverse is also true a changing electric field creates

2 Electromagnetic Waves Electromagnetic waves are produced when something - an electric charge that When an electric charge vibrates, the electric field around it Because the electric charge is in motion, it also has a This magnetic field also as the charge vibrates. As a result, the vibrating electric charge is surrounded by Electromagnetic Waves This is what creates electromagnetic waves The changing magnetic and electric fields Electromagnetic Waves Examples of EM waves include These different waves have different Also known as Speed of EM Waves All EM waves travel in a vacuum Different but the same They travel at what we call the Speed of light in a vacuum = m/s That s m/s! Or miles per second! Almost times faster than sound Speed of EM Waves Describe Michelson Experiment: Figure 3 page 534 in your textbook Speed of Light Nothing travels In matter, the speed of electromagnetic waves depends on

3 Wavelength and Frequency Wavelength and frequency have as they do with mechanical waves The different types of EM waves have different Unit of frequency is still AM radio KHz = FM radio MHz = Speed = Since the speed is the same for all EM waves, as the frequency increases, Is EM radiation a Wave or a Particle? EM radiation is strange because it sometimes seems to behave as a and sometimes seems to behave as a This is called the EM Radiation as a Wave Light and other EM waves exhibit many wave properties such as EM Radiation as a Wave 1801 Thomas Young s Showed that light exhibited This is a characteristic of Describe Demonstration: Figure 5 page 536 in your textbook EM Radiation as a Stream of Particles First proposed by Light travels in Light casts a shadow does not Idea abandoned for over years 1887 Heinrich Hertz discovers the Hertz found that whether or not electrons were ejected depended on the of the light and not the Blue light works but red light does not Photoelectric Effect Figure 6 from page 537 in your textbook

4 Photoelectric Effect In 1905 explained the photoelectric effect Wins Nobel Prize for this EM radiation is a stream of particles called EM radiation of different frequencies have photons with different Photoelectric Effect Blue/violet light is a frequency than red light Therefore blue/violet light photons have energy than red light photons Describe Demonstration of phosphorescence with various colors of light: Dual Nature of Light Photoelectric effect does not depend on the of waves but the Since there is evidence for light as a and light as a, both are acceptable The Dual Nature of Light Intensity Intensity = The intensity depends on the and the Energy is as you get farther from the source Intensity Describe demonstration of big light bulb and Christmas light bulb: Describe demonstration of lab activity:

5 Section 18.2 Everyone is familiar with the visible spectrum _ In 1800 William Herschel found that the colors of the spectrum have different He also discovered that the area just past the red end of the spectrum was He concluded that there is radiation Electromagnetic waves can have a wide variety of. The entire range of EM wave frequencies is known as Figure 9 page 540 in your textbook Radio Waves Radio waves have the frequencies and the wavelengths of the EM spectrum Uses for radio waves include the following AM and FM Radio AM radio has frequencies than FM radio AM = FM = AM radio has waves than FM AM =, the amplitude of the waves is varied to carry the message FM =, the frequency of the waves is varied to carry the message AM and FM Radio Figure 10 page 541 in your textbook Whichever way the signal is sent, your radio

6 Television A television signal is The EM waves carry information about The frequency of television signals is in the same range as Microwaves Microwaves are the radio waves Wavelengths are In a microwave oven, Why is there a screen on the front? Why is there a turntable? RADAR RADAR = Radio waves are sent out and Can be used to find out RADAR speed gun changes the of reflected waves The faster the object is moving, Infrared Higher frequency than, lower frequency than Transmit All objects give off infrared but warm objects Thermogram = These are used to Infrared Figure 12 from page 543 in your textbook Visible Light Different colors have Red end has waves, frequencies Violet end has waves, frequencies

7 Ultraviolet frequency than violet light Cause Can cause Used to kill => In small doses, Generally, we try to avoid exposure to UV _ DEMO: UV beads X-Rays frequency, waves than UV Higher frequency means This is why x-rays Absorbed by Used in airport security Gamma Radiation Highest frequency, shortest wavelength EM radiation Can penetrate most objects Can be blocked by Used to Fine beam of gamma radiation can without In order of increasing frequency, decreasing wavelength AM and FM radio television Microwaves RADAR Figure 9 page 540 in textbook