What is light? • An electromagnetic wave that can be seen by the human eye. • Can travel either in matter or empty space.
The Speed of Light • Nothing travels faster than the speed of light! • Light travels at a speed of 300,000 km/s- that’s like going around the Earth 7 times in a second!! • Sun travels about 150 million km to Earth in only about 8 ½ minutes. • Light travels fastest in empty space and slowest in solids.
Wavelength and Frequency • Wavelengths of light are short- measured in nanometers (nm). • 1 nm = 1/1,000,000,000 m • Different waves of light have different wavelengths and frequencies.
So, what is a light wave? • A transverse wave that contains vibrating electric and magnetic fields. • Intensity: measure of the amount of energy that the wave carries. In light, it determines the brightness of the light.
The Electromagnetic Spectrum • The complete range of electromagnetic wave frequencies and wavelengths is called the Electromagnetic Spectrum
Radio Waves and Microwaves • Waves that carry radio and television signals to your home are RADIO WAVES • The wavelengths are greater than about 0.3 meters and some are even thousands of meters long. • Shortest radio waves are called microwaves- not just for cooking, they’re used to transmit info to and from cell phones, too!
Infrared Waves • Remote controls use infrared waves. • Have wavelengths between 0.001 m and 700 billionths of a meter. • Warm bodies emit infrared waves • Night vision goggles use technology that is sensitive to infrared waves.
Fun Fact! • All bodies with a temperature above absolute zero emit electromagnetic waves. As the temperature of an object increases, the wavelengths emitted decrease. At room temperature, objects emit mostly infrared waves.
Visible Light and Color • Between 700 and 400 billionths is special… it’s what we can see! • This is called Visible Light • White light (from the Sun or a flashlight) is really a combination of all colors
Visible Light and Color • You can see this by using a prism to separate white light into different colors. • When the light passes through the prism, the different wavelengths of light are bending different amounts. Violet light is bent the most because it has the shortest wavelength. Red light is bent the least.
Ultraviolet Waves • Waves with wavelengths between about 400 billionths and 10 billionths of a meter are UV waves • Shorter than visible light and carry more energy than visible light waves. • Although excessive exposure to UV waves can be dangerous, some exposure is needed to make vitamin D, which helps form healthy bones and teeth.
X Rays and Gamma Rays • The highest energy, highest frequency, and shortest wavelengths. • X Rays are used to examine injured bones- the rays pass through soft tissue but are blocked by denser body parts. • X rays are also used to kill cancer cells • Gamma Rays are used to kill bacteria that cause food to spoil. But don’t worry…
How we actually SEE light • You see an object when light emitted or reflected from the object enters your eye. • 1st: cornea • 2nd: transparent lens- changes shape and enables you to focus.
Why do objects have color? • When light waves strike an object, some of the light waves are reflected. The wavelengths of the light waves that are reflected determine the object’s color. • For example: a red rose reflects light waves that have wavelengths in the red part of the spectrum. Your green shirt reflects light waves that have wavelengths in the green part of the spectrum.
Rod and Cone Cells • The retina contains over one hundred million light-sensitive cells called rods an cones. • Rods are sensitive to dim light; Cone cells enable you to see colors. • There are 3 types of cone cells: one is sensitive to red and yellow light, another is sensitive to green and yellow light and the 3rd is sensitive to blue and violet. • The combination of the signals sent to the brain by all three types form the color you see.
Common Vision Problems • Nearsightedness: can see nearby objects clearly, but distant objects are blurry. • The eyeball is too long, so light from far away objects are brought to a focus before they reach the retina. • Farsightedness: can see distant objects clearly, but cannot focus clearly on nearby objects. • The eyeball is too short, so light from nearby objects have not been brought to a focus when they strike the retina. • Pg 204
Common Vision Problems (cont’d) • Color blindness: the inability to perceive differences between some colors that other people can distinguish because either the rods or cones are not functioning.
Why are there so many songs about arcs of Electromagnetic Radiation with wavelengths between 380 and 750 nm in concentric bands formed by the refraction and reflection of solar energy off of moisture in the Earth’s atmosphere? And what’s on the other side?