Chapter 22.1

 Light travels fast and over long distances  Light carries energy and information  Light travels in straight lines  Light bounces and bends when comes in contact with objects  Light has color  Light has different intensities, bright or dim

Light is a form of energy. Light is produced when electrons move around within the nucleus of an atom. In order to get light out of an atom you must put some energy into the atom. One way is heat. The process of making light with heat is called incandescence.

 Incandescent bulbs pass electric current through a thin metal wire called a filament.  The filament heats up and gives off light.  Fluorescent bulbs are another kind of electric light and are more efficient.  To make light, fluorescent bulbs use high-voltage electricity to energize atoms of gas in the bulb.

 Planck’s constant is used to measure the energy emitted by light photons.  E = hf  Where h = planck’s constant X J. S  f = frequency

 Since the late 1600’s, scientists have debated whether light is a wave or a particle.  In modern times, they have concluded that it has the properties of both a wave and a particle.

 When light travels, it acts like a wave.  Light behaves as a transverse wave, because the wave vibrates in all directions.  To make the waves vibrate in one direction, you must pass it through a filter.  The new parallel waves are said to be polarized.

 When light is given off or absorbed by objects, it acts like a particle.  When high energy light strikes a metal, electrons are released.  This is what is called the photoelectric effect.

 Light emitted from the sun or from a light bulb travels in straight lines out from the source.  Intensity is used to describe the amount of light energy per second falling on a surface.  As the distance from a light source increases, the light intensity decreases.

 Sound travels slower than light.  The speed of sound is 340 m/sec.  The speed of light through air is approximately 300,000,000 m/sec or 186,000 miles per sec.  The symbol for the speed of light is c.  C = 3 X 10 8 m/s  Light is so fast that it can travel around the entire Earth 7 ½ times in 1 second.

 When light moves through a material it travels in straight lines.  Reflection occurs when light bounces off of a surface. Ex. Image in a mirror  Refraction occurs when light bends crossing a surface or moving through a material. Ex. Light rays traveling through water.

 Starlight must travel from space through Earth’s atmosphere which varies in temperature and density.  Cold pockets of air are more dense than warm.  Starlight is refracted as it travels through various temperature pockets in atmosphere.  So, the image of a star appears to “twinkle” or move because the light coming to your eye follows a zigzag path due to refraction.