Chapter 14 Light

Chapter 14 Light

I.  What is light?

     A.  Light is a form of energy  

            1. Light travels in waves.

            2. Sources of light

                a. The sun is the major source of light.

                    (1) Warms Earth

                    (2) Allows plants to make their own food

                b. A fire is important to life on Earth.

                    (1) Provides warmth

                    (2) Allows people to cook food

                c. a light bulb

                    (1) Thomas Edison and Joseph Swan invented the light bulb.

d. Some animals are bioluminent.

                    (1) The light is caused by a chemical reaction in their body.

                    (2) A firefly

     B. Shadows

             1. Light travels in straight lines called rays.

             2. A shadow is a dark area that appears where light can’t reach.

             3. The angle light strikes the object affects the size of the shadow.

a. At noon shadows are the shortest because the sun is highest in the sky.

b. Early in the morning or late in the day your shadow is longer because the sun is low in the sky.

C. Visible light, ultra violet light, infrared, microwaves, and x-rays are all   part of the electromagnetic spectrum.

            1. We see only the colors in the visible spectrum.

            2. The colors in white light can be separated by a prism.

                 a. red

                 b. orange

                 c. yellow

                 d. green

                 e. blue

                 f. violet

             3. White light and the colors of light are called the visible spectrum

                  a. Each color of light has its own wavelength and frequency
                        (1) Violet has the shortest wavelength and the highest
                         frequency.

                        (2) Red has the longest wavelength and the lowest
                        frequency            

              4. Electromagnet waves we can not see

                  a. Radio waves, microwaves, and infrared waves are invisible
                  because their wavelengths are too long for the human eye to see.

 b. Ultraviolet waves, x-rays, and gamma rays are invisible
        because their wavelengths are too short for the human eye to
        see.

II.  How light travels?

     A.  Light travels from a light source in straight lines called rays.

     B.  Light waves can be absorbed, reflected, or transmitted.

     C.  Objects absorb or take in some of the light that hits them.

            1. Light waves become a form of heat energy.

            2. Black objects get warmer because they absorb all the light

               that hits them.

     D.  Objects reflect or bounce back some of the light that hits them.

     E.  We see colors because objects absorb some frequencies of light

           and reflect others.

            1. A shirt looks red because it reflects light rays of red frequencies

            and absorbs all other color frequencies.

            2. A white shirt reflects all colors of the visible spectrum.

            3. A black shirt looks black because it absorbs all the colors

            of the visible spectrum.

     F.  Transparent objects transmit or allow light to pass through so that you
          can see what is behind it clearly.

           1. They absorb some light

           2. They transmit or let pass through the color of light we see.

     G.  Translucent objects allow light to pass through but scatters it so

           what is behind it cannot be seen clearly.

           1. They absorb some light

           2. They transmit or let pass through the color of light we see.

     H.  Opaque objects don’t allow light to pass through.

           1.  They reflect whatever light they don’t absorb.

           2.  Their color is the color of light they reflect.

           3. Foil, brick, wood, and your body are opaque objects.

     I.  Mirrors

          1.  reflect light to form an image

          2. shiny, smooth surface

           3.  light reflects at the same angle that it hits the mirror

           4. they form a good image

     III.  Bending Light

       A.  Light travels at different speeds through different materials and can be bent.

            1. The bending of light is called refraction.

        B. Light does not need a medium to travel through.

        C. Light travels the fastest through a vacuum such as outer space.

        D.  White light changes speed and direction.

             1.  Light waves refract as they travel from air to water.

                  a.  Going from air to water, light slows down.

                  b.  Light changes direction when it slows down.

        E. The Human Eye

            1. A muscle called an iris controls how much light enters the eye.

            2. The lens refracts the light rays and forms an upside down image

            on the retina of the eye.

            3. Signals travel along the optic nerve to the brain.

            4. You see right-side up images.

        F. Lenses

             1. All lenses have at least one curved surface .

             2. Lenses refract light to form an image.

             3. Convex lenses are thicker in the middle than the edges,

                 somewhat like a football

                a. The light rays bend in the middle and come together on the

                 other side of the lens.

                b. Convex lenses magnify things.

                c. A magnifying glass and a microscope are convex lens.

             4.  Concave lenses are thinner in the middle than at the edges

                   a. makes objects look smaller

                   b. spread light rays apart

                   c. helps you view a larger area

                   d.  used on a passenger side of a car

                   e.  used in stores to see the entire store

   IV.  Light Waves

         A.  The distance from the highest point in one wave to  

                the next highest point is a wavelength of light.

               1. Different colors of light have different wavelengths.

               2. A crest is the highest point of a wavelength.

               3. A trough is lowest point of a wavelength.

               4.  Other kinds of energy that use waves are

                    a. microwaves

                    b. x-rays

                    c. radio waves

                    d. A laser produces an extremely powerful beam.

                           (1) Laser light can be visible or invisible.

                           (2) used to store information on a CD

                           (3) used for barcodes in stores and libraries