EM Spectrum
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EM Spectrum order (longest wavelength -> shortest)
Radio -> Microwave -> Infrared -> Visible -> UV -> X-ray -> Gamma rays
Radio waves uses
communication, remote controls, MRI machines
Microwaves use
cell phones (and other communication), cooking food, radar
Infrared uses
thermal imaging
Visible Light uses
human vision
Ultraviolet uses
sterilizing surface equipment, vitamin D production
X-Ray uses
medical diagnoses, cancer therapy (and causes), security (airport)
Gamma Ray uses
medical diagnoses, cancer therapy (and causes),
What do the numbers on the radio dial represent?
The numbers on your radio dial represent frequencies used by your local radio stations.
Why can you see your reflected image in a mirror, but not in a smooth wall?
The very small bumps on the wall don’t allow the light to perfectly reflect how it needs to in order to form a clear image. The light rays scatter too much to produce an image.
Transparent
a material that allows almost all light to pass through, where objects can be seen clearly (light not scattered)
Translucent
a material that allows some light to pass through, where objects appear blurry (scattered light)
Opaque
a material that does not allow light to pass through, and objects cannot be seen through it. All light is either absorbed or reflected.
Black objects
-absorb all colors, so no light is reflected back to your eyes.
White objects
reflect all colors
Rods
work at low levels of light (night vision). They don’t interpret color.
Cones
used for brighter light and colors. (Think traffic cones; they’re bright yellow)
Why is the sky blue?
Due to Rayleigh Scattering * When white light enters the atmosphere, it separates and scatters in all directions. -> Blue wavelengths are shorter, so they scatter more than other colors. Colors with longer wavelengths (red, orange, etc.) don’t scatter as easily
Why isn’t the sky violet?
Light is not evenly distributed by color. There is more blue light than violet light in the atmosphere because more violet light is absorbed high in the atmosphere. Our eyes are also more sensitive to violet light. Our vision doesn’t pick up violet as easily as blue.
Why is the sky red/orange/yellow during a sunset?
Since the sun is lower on the horizon during sunset, the light travels through more atmosphere to your eyes than it does during the day. This means that there will be more refraction of the light as it travels from one medium (outer space) to another (the atmosphere). The blue and violet wavelengths scatter first away from your eyes. This leaves the longer wavelength colors to enter your eyes.
Speed of light?
3 x 10^8