Light Properties

LightDixie STEM Workshop

Dr. Tracey Wheeler

What is Light?

• Light is a form of electromagnetic radiation. • What is electromagnetic radiation?

Electromagnetic Radiation

Electromagnetic radiation can be described in terms of a stream of mass-like particles, called photons, each traveling in a wave-like pattern at the speed of light. Each photon contains a certain amount of energy.

Starting with the lowest energy (longest wavelength) and moving to the highest energy (shortest wavelength). This is often referred to as the electromagnetic spectrum. http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

Properties of Electromagnetic Radiation

• Travels in waves and is referred to electromagnetic waves

• Electromagnetic waves travel at the same speed but differ in wavelength and in frequency. All electromagnetic waves, including light rays travel in a vacuum at a speed of light- 186,282 miles/second. It takes 8 minutes for light to travel from the Sun to Earth.

• Does this mean that the distance light travels depends on size or brightness of the light source?

Wavelength

A wavelength is the distance between corresponding parts of two waves with the same motion.

Wavelength, Velocity, Frequency, and Speed

Frequency- the number of waves that pass by a point in a specified amount of time. Speed- equals the wavelength x frequency

Frequency

Waves with long wavelengths have low frequencies; waves with short wavelengths have high frequencies.

Visible light• Visible light -Cone-shaped cells in our eyes

act as receivers tuned to the wavelengths in this narrow band of the spectrum. Other portions of the spectrum have wavelengths too large or too small and energetic for the biological limitations of our perception. Visible light 700 nm to 380 nm

• Do nocturnal animals see in total darkness?

• http://www.ebiomedia.com/how-do-animals-see-in-the-dark.html

Properties of Light

Light travels in straight lines, even when it is made to change direction. 1. A thin line of light is called a ray.2. A beam of light is made up of many rays.3. Light travels faster than sound- astronomers use it for measuring great distances.

ReflectionTo see an object that does not produce it's own light, three things must happen.1. There must be a light source2. The light must strike the object3. The light must be reflected from the object and then travel to the eye.

Can light travel around things, not just in straight lines?

Refraction of LightWhen light rays strike a transparent material at an angle of 90 degrees, they travel in a straight line and gradually slow down. When light rays pass at a slant or angle from one transparent material (air) into another transparent material (water) they are bent or refracted, so they travel in a different direction. Light is bent because there is a change in the speed of light as it passes from one transparent material into another. This depends on the materials optical density.

Color

• When a beam of sunlight is passes at a slant into a prism, it is separated into a band of colored light, called the spectrum (visible light)

• White light is really a mixture of six colors• Colors make up the spectrum all have different wavelengths• Blue light is the shortest wavelength

Color• A material looks a certain color

because when white light strikes the material, some colors are absorbed and others are reflected to the eye.

• For example, a red dress may look red because all the colors of white light are absorbed except red, which is reflected back to the eye.

Why during the day does the sky appear blue?

Sky appears blue because blue light is scattered by the dust and reflected to the eye much more than are the other colors.

Is color a property of reflected light?