# Light Chapter 10. Standards: P4a: Identify the characteristics of electromagnetic and mechanical waves. P4b: Describe how the behavior of light waves.

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Light Chapter 10

Standards: P4a: Identify the characteristics of electromagnetic and mechanical waves. P4b: Describe how the behavior of light waves is manipulated causing reflection, refraction, diffraction and absorption. P4c: Explain how the human eye sees objects and colors in terms of wavelengths.

Section 1: Properties of Light

1) Light is a type of energy that travels as an electromagnetic wave and does not require a medium.

2) Electromagnetic waves are created when electricity and magnetism oscillate – or move back and forth.

3) The entire range of possible frequencies of electromagnetic energy is called the electromagnetic spectrum. The spectrum ranges from Radio Waves (low energy) to gamma rays (high energy.) http://www.youtube.com/watch?v=cfXzwh3KadE

4) Energy that we can actually see within the spectrum is called white light. White light contains all of the colors of the rainbow. (ROYGBIV)

5) Color is how we perceive (or see) the energy of light. Every color of light has a different energy, and therefore a different wavelength and frequency.

6) For visible light, red light has the lowest frequency and longest wavelength, while violet light has the highest frequency, and shortest wavelength.

Section 2: Color and Vision

1) We see because light is reflected in to our eyes. Light enters our eyes through the lens and lands on the retina – cells on the retina transmit signals to the brain which then interprets color.

1a) Cells in your eyes that help you see are called rods and cones: 1b) Rods respond to black and white, while cones respond to the colors red, green and blue. 1c) You have more rod cells than cones; that is why our color vision is less sharp than black and white

Chapter 23

2) The color an object appears to be is the color of light it reflects. A blue shirt looks blue because it reflects blue and absorbs all other colors.

2a) White objects appear white because they reflect all colors of light, and remember, all colors of light mixed together make white light.

2b) A black object appears black because it absorbs ALL of the colors of light.

Color Mixing Web SiteColor blindness Remember that colors of light and colors of pigments mix differently!

Section 3: Optics (More wave interactions)

1) Four things can happen when light interacts with matter: a) Light can pass through unchanged (transparency) b) Light can pass through but be scattered (translucency) c) Light can bounce off (reflection) d) Light can transfer its energy to the material (absorption) All four interactions usually occur at once.

2) Materials that allow light to pass straight through are transparent (glass, clear plastic, clean air)

3) Materials that scatter light are called translucent (frosted glass, tissue paper)

4) Mirrors are surfaces that reflect light – they can be concave or convex Concave mirror Convex Mirror a) Concave mirrors are shaped like CAVES b) Convex mirrors are shaped like the back of a spoon

5) Lenses refract light – they can be concave or convex a) Concave lenses are shaped somewhat like an hourglass and spread light rays over a larger area, and make things appear smaller b) Convex lenses are shaped like footballs and focus light into a smaller area, making things appear bigger

Refraction

Making a connection between Lenses and Mirrors – Spreading it Out

Making a connection between Lenses and Mirrors: Bringing it Together

Comparing and Contrasting Lenses and Mirrors

The images below explain how nearsightedness and farsightedness can be corrected with glasses.

6) Prisms reflect AND refract light. Because of its shape, when a prism refracts light it separates light into its different wavelengths to create a rainbow.

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