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## Unit 32 Electromagnetic RadiationPresentation Transcript

• Electromagnetic Waves and the Electromagnetic Spectrum
Unit 32
• Electromagnetic waves perpendicular waves combing the electric and magnetic fields.
• Electromagnetic waves are produced when an electric charge vibrates or accelerates and can travel through empty space or through matter.
• Fig. 1. Electromagnetic spectrumThe electromagnetic spectrum is made up of many different types of electromagnetic waves. The frequency and wavelengths of these waves determine the type of electromagnetic wave. Figure 1 shows the electromagnetic spectrum and its waves.
• Which of the following is NOT an example of an electromagnetic wave?
A. X-ray
B. Microwave
C. Visible light
D. Sound wave
• Which of the following is NOT an example of an electromagnetic wave?
A. X-ray
B. Microwave
C. Visible light
D. Sound wave
• Behavior and Color of Light

Interactions of Light

When light strikes a new medium or substance, the light can be reflected, absorbed, or transmitted. When light is transmitted it can be refracted, polarized, or scattered.
• Scattering and Refraction
Why is the sky blue?
• Scattering and Refraction
• Have you ever wondered why the sky is blue during the day and reddish orange at dusk?
• It is due to the scattering of the light rays (REFRACTION).
• The sunlight gets scattered by the molecules of the atmosphere.
• Particles in the atmosphere scatter shorter wavelength blue light more than the longer wavelength red light.
• Light Paths in our Atmosphere
Red light goes straight through the atmosphere.
Blue light scatters all over.
Thus, you see the sky as blue. If blue light did not scatter, the sky would be black
• Sunset in our Atmosphere
Larger particles like dust and water droplets reflect red light causing dusk and dawn to look red and orange.
• Refraction
Refraction is the bending of light that is caused by a change in speed when the light wave goes from one medium into another.
Figure 32.2.2 demonstrates this concept.
• Refraction
Refraction is the bending of light that is caused by a change in speed when the light wave goes from one medium into another.
That is why things appear to be somewhere they are not underwater.
• Reflection
• Reflection of a light wave occurs when the light wave bounces off an object.
• The Angle of Incidence is equal to the angle of reflection.
• These angles are always measured from a line perpendicular to the surface.
• Scattering
• Light Producers
• An object that produces light is called a luminous object. Luminous objects include the sun, light bulbs, lightning, and hot objects, etc.
• All objects produce electro-magnetic waves.
• Most produce low frequency radiowaves. Only very hot or energetic objects produce wavelengths that can be seen by our eyes.
• Light Reflectors
• Most objects that we see with our eyes do not produce their own light and must rely on the reflection of light in order for us to see them.
• For example, as light hits your shirt the color your eye detects is the color of light that has been reflected or re-emitted by your shirt.
• Most of the other colors were absorbed by the materials.
• Light Sources
Objects that give off their own light are said to be luminous. Some common luminous objects that you are aware of are the sun, incandescent light bulbs, fluorescent light bulbs, lasers, and neon lights.
• Glowing Objects
Incandescent light is light that is produced as a result of a glowing hot object.
Light bulbs that have filaments in them have an electric current pass through them. As a result of this electric current, the filament heats up and begins to glow, giving off light.
• Flourescence
• Fluorescent light is created by a process called fluorescence. In a fluorescent light there are two electrodes, one on each end of the tube, phosphor powder, and mercury vapor.
• The electric current comes in at one electrode and transmit the electrons into the gases.
• The mercury atom electrons get excited, jump to a higher energy level, and then drop back down to their original energy state. When the electrons return to their original state they emit photons, seen as visible light of all different frequencies and wavelengths.
• Mercury
Fluorescent bulbs do not get very hot and they are more energy efficient than incandescent bulbs;
However, the proper disposal of a fluorescent light bulb requires attention because it contains toxic mercury.
A fluorescent bulb that has burned out should be brought a recycle center.
To find a recycle center near you, go to Electronics: Earth 911 and type in fluorescent light bulbs and your zip code in the top.
• Electromagnetic Waves
Characteristics of Electromagnetic Waves
Transverse Waves
Alternating electric and magnetic fields
Characteristics of waves and particles
All travel at 3.0 x 108 m/s (Speed of Light)
It takes 8 minutes for light to get from the Sun to Earth
It takes 3 seconds for radio signals to get from Earth to the Moon
• Electromagnetic Spectrum
Includes the following types of waves
Microwaves
Infrared
Visible Light
Ultraviolet
X-Rays
Gamma Rays
Radio waves are used for radio, cell phones, remote controlled devices, GPS/satellite communications, and television.
Microwaves are the shortest wavelength radio waves and are used in many communication functions.
Radar is used to determine how fast an object travels. It incorporates the use of radio signals, receivers, and the Doppler effect in order to determine the speed of an object.
• Infrared Waves
Infrared waves are heat waves.
All objects emit infrared waves because all objects possess heat.
Night vision goggles detect infrared waves and allow the user to see the movement of objects in the dark.
Many TV remotes use infrared.
• Infrared image of a human body. Red is hot, blue is cool.
• Visible Light
Our eyes detect electromagnetic energy in a small portion of the electromagnetic spectrum called the visible light region.
The visible light region corresponds the wavelengths and frequencies of red, orange, yellow, green, blue, indigo, and violet light.
• Ultraviolet Waves
UV Light that is at a higher frequency and energy than violet light.
UV light can kill micro-organisms.
Too much exposure can cause:
Sunburn, Wrinkles, and skin cancer
As it damages cell DNA
• X-Rays
X-Rays have high energy and can penetrate some material.
Used in:
Medicine
Industry
Transportation
Too much exposure can damage
living tissue or even cause cancer.
• Gamma Rays
Gamma rays are the highest energy electromagnetic wave.
They usually come from radioactive elements or stars
Uses include:
Killing cancer cells
Making pictures of the brain
Inspection tools in industry
• Speed of Electromagnetic Waves
All electromagnetic waves travel at 3.0 x 108 m/s in a vacuum.
Speed of a wave formula:
Speed = Frequency x Wavelength
As the frequency increases, the wavelength decreases.
See the next slide for a diagram of this relationship.
• Electromagnetic Spectrum Diagram
Diagram of Electromagnetic Spectrum (including the relationship between frequency and wavelength).