The Electromagnetic Spectrum and Light (Sections 18.1-18.3 only) Chapter 18 The Electromagnetic Spectrum and Light (Sections 18.1-18.3 only)
18.1 Electromagnetic Waves
What Are Electromagnetic Waves? EM waves consist of changing electric fields and magnetic fields. EM waves carry energy from place to place.
How are EM waves produced? When an electric field changes, so does the magnetic field. The changing magnetic field causes the electric field to change. When one field vibrates—so does the other. EM waves are produced when an electric charge vibrates or accelerates. In other words it is produced in constantly changing fields.
How are EM waves produced? Electromagnetic waves are produced when an electric charge vibrates or accelerates. See animation here Back up link #3
How they travel EM waves can travel through a vacuum, or empty space, as well as through matter. This is called electromagnetic radiation.
Did you know? The speed of light is constant in a vacuum. Speed of light (c) = 3.00 x 108 m/s
Wavelength and Frequency EM waves vary in wavelength and frequency despite traveling at the same speed. Speed of light (c) = wavelength x frequency
Quick Facts Speed: 3.0 x 108 m/sec (speed of light) Wavelength: varies Frequency: varies Travels in a straight line (need satellites to account for this problem) Video Clip (3:28)
18.2 Electromagnetic Spectrum
Electromagnetic Spectrum Radio waves Infrared rays Visible light Ultraviolet rays X-rays Gamma rays
Radio Waves AM (frequency is the same and amplitude changes) FM (frequency changes and amplitude is the same)
Which is AM radio?
Television Waves Same as radio but also sends pictures.
Microwaves Waves of this frequency are absorbed by water and heat food. Food is in motion and therefore creates heat
How is a cell phone like a microwave?
Get off the phone! 10950 watts is the same as 1.09 kWatts
Now tell me how a cell phone is like a microwave!! If you talk on cellular phone more than 20 min. your brain temperature raises for up to 2 degrees.
Low wavelength, frequency & energy
Infrared Rays Used as a source of heat Discover areas of heat differences Can’t see but skin can sense.
A thermogram can be used to diagnose problems in a utility line.
More Thermograms What color is showing cooler temperatures?
Visible Light The only part of the spectrum the human eye can see. Each color of light corresponds to a different range of wavelengths.
How to remember order Red part of visible light it towards Infrared Violet part of visible light is towards ultraviolet
Ultraviolet Rays Uses in health and medicine, and in agriculture. helps your skin produce vitamin D used to kill microorganisms Treats jaundice in newborn help plants grow. Negative: Can cause skin cancer and blindness in humans
X-rays Used in medicine, industry, and transportation to make pictures of the inside of solid objects.
I can see that!
Gamma Rays Used in the medical field and in industrial situations as an inspection tool. used to make pictures of the human brain used in radiation therapy to kill cancer cells used to check pipes by taking pictures to look for rusting, cracks, or other signs of damage.
Electromagnetic Spectrum You will make a chart similar to this but far more detailed.
Keep in mind The electromagnetic spectrum can be expressed in terms of energy, wavelength, or frequency. Frequency is measured in cycles per second (which is called a Hertz) Wavelength is measured in meters Energy is measured in electron volts.
Let’s compare them.
18.3 Behavior of Light
How does light do that? When light strikes a new medium, the light can be Reflected Absorbed Transmitted.
Reflection Regular – light waves hit a smooth surface
Reflection Diffuse – light waves hit a rough surface and reflects light in many different directions.
Regular (same as Specular)
How does light do that? When light is transmitted, it can be Refracted Polarized Scattered.
Refraction Light refracts (or bends) when it moves from one medium to another. What are the 2 mediums shown here?
Polarization A vertical polarizing filter blocks light that is horizontally polarized.
Polarization A horizontal polarizing filter blocks light that is vertically polarized.
Polarization Put them together and almost ALL light is blocked out. View Clip
Scattering Light is redirected as it goes thru a medium. Blue, green, and yellow wavelengths of sunlight are heavily scattered in certain weather conditions. What color is left?
The Color of the Sun
The “science” behind it Description: at sunrise and sunset the sun is yellow, orange or red Physical process: Rayleigh scattering by air molecules and fine dust particles. Explanation: on clear days only the blue light is scattered away, on hazy days the yellow and the orange wavelengths are also scattered and only the red remains in the direct solar light. Conclusion: Red sunsets suggest that there is dust in the air (pollution, haze over the ocean, volcanic activity, dust storms).
The Timing of the Sunset & Sunrise We see the sun before it actually rises above the horizon and after it sets below the horizon.
Twilight
Flattening of the Sun’s Disk at Sunset Green flash
Your thinking, “Ms. Lolich first the Hulk and now this?” Green Flash? Your thinking, “Ms. Lolich first the Hulk and now this?”
Green Flash They are usually seen at an unobstructed horizon, such a Higher frequency light (green/blue) curves more than lower frequency light (red/orange), so green/blue rays from the upper limb of the setting sun remain visible after the red rays are obstructed by the curvature of the earths over the ocean.
Development of Green Flash
A larger than usual green flash in Santa Cruz
Stages of a green flash
Quiz: Regular or Diffuse?
As the wavelength decreases from the red end of the spectrum to the violet end, what happens to the frequency? It remains constant. It increases. It decreases. It is impossible to predict what will happen.
As the wavelength decreases from the red end of the spectrum to the violet end, what happens to the frequency? It remains constant. It increases. It decreases. It is impossible to predict what will happen.
The End