Sources of Light 4-5.1 Our primary source of light is the sun. We also have other sources of light: (both natural and man-made)
ENGAGING SCENARIO 1 I spoke to the park ranger and reported your conclusions about how electricity and magnetism are related, and how electricity can be used to produce heat, light, motion, and sound, and he gave me another challenge for you. He wants us to examine the properties of light. He gave us some prisms. What do we have to investigate here?
Separating Light (4-5.1) Sir Isaac Newton discovered that sunshine (white light) is made up of many colors. He passed a beam of white light through a prism (a triangular piece of glass that allows light to spread into a band of 6 colors). These colors are called the visible spectrum. They are Red, Orange, Yellow, Green, Blue, Indigo, and Violet (ROY G BIV). The prism spread the colors out by refracting (bending) them at different angles. He then sent the light back through a 2 nd prism where the light became white once again.
The most common example of a spectrum is the rainbow created in nature. The rainbow is caused by sunshine (white light) shining on water droplets that are in the air just after a summer shower. Thousands of these water droplets break up the light, just like Sir Isaac Newton's prism.
ENGAGING SCENARIO 2 I spoke to the park ranger and reported your conclusions about how light, is a form of energy, and is made up of many different colors. Are you ready for another challenge? This time the park ranger wants you to investigate how light travels. What do we have to investigate here?
Light travels in a straight line away from the light source. Light travels in waves. Light waves travels much faster than sound; light from the sun takes less than 8 ½ minutes to travel 93 million miles (150million kilometers) to reach Earth. *light thru cards How does light travel? (4-5.3)
Brightness of Light *The intensity of light or brightness of the light is related to the amount of light being seen. *The closer the source of the light, the greater the intensity or degree of brightness *The greater the distance the source of the light, the lesser the intensity or brightness (flashlight)(website)
Light behaves differently when it strikes different types of materials. (4-5.4) If light travels through an object it is TRANSPARENT Objects can be seen clearly when viewed through transparent materials Air, glass, and water are examples
TRANSLUCENT Scatters or absorbs some of the light that strikes it and allows some of the light to pass through it Objects appear as blurry shapes when viewed through translucent materials Waxed paper, frosted glass, and cafeteria windows are examples If some light passes through but not all and a light shadow is present it is
If light is blocked by an object and a dark shadow is cast it is OPAQUE Does not allow light to pass through Light is either reflected from or absorbed by an opaque material Wood, metals, and thick paper are opaque materials
What will happen when light hits these objects? Cardboard Glass of water School bus window Tissue paper Plastic wrap Handlens Picture frame glass
Light travels in straight paths called rays, until it hits an object where it may be: Reflected - bounced back from a surface Allows objects to be seen that do not produce their own light (Example-moon) When light strikes a smooth,shiny object (mirror)it is reflected so that a reflection looks very similar to the object The color of the light that is reflected from an object is the color that the object appears. Ex.- A red apple appears red, because it only reflects red light.
Refraction- light passing from one type of transparent material to another; making it change directions Examples: When light travels through a magnifying glass, it changes direction, and we see a larger, magnified view of the object. When a straw is viewed in water, light passes from the water to the air causing the path of the light to bend. When the light bends, the straw appears distorted (bent or broken.)
Absorption- the light does not pass through or reflect from a material. It remains in the material as another form of energy. The colors of objects are determined by the light that is not absorbed but is reflected by the objects. All other colors of light striking the object are absorbed by the object. A blue car, for example, reflects blue colors of light and absorbs all other colors. Black objects absorb all colors. White objects reflect all colors.