5.2: Behavior of Light

• Light is a form of energy that travels at 3.0 × 10^8 m/s in a vacuum but at lower speeds in denser material media.
• 3.0 × 10^8 m/s


  This speed is theoretically considered as the highest possible speed in the universe.
• Light travels in a straight path and tends to spread out from the source.
• In some sources such as lasers, light spreads out less.
• Light interacts with matter, which can affect its behavior in different ways.
• Transmission is the passing of light through a material medium.
• The extent of the transmission of light depends on the type of the material.
• Transparent and translucent materials transmit light, but opque materials do not.
• If light is not transmitted, it may have been reflected or absorbed.
• Dispersion is the separation of light into different colors. This may happen to a refracting light depending on the angle from which it entered a new medium and the nature of this medium.
• White light is dispered into a band of colors: red, orange, yellow, green, blue, indigo, and violet.
• Absorption happens when a material takes in light and converts it into different forms of energy.
• Opaque materials are those that selectively absorb colors
• Most opaque materials around us ocnert light to heat but some materials, such as leaves and photovoltaic cells, convert some of the light to other forms of energy such as chemical energy stored as glucose and electrical energy, respectively.
• White light is composed of different components of a spectrum: red, orange, yellow, green, blue, indigo, and violet.
• When an object reflects all the components of light, it appears white.
• However, when an object absorbs all the components of light, it appears black.
• An object that appears with a particular color means that the object absorbs most of the colors and reflects only the color of the object.
• Scattering is the splitting and bending of light into several random directions.
• For a transparent material, scattering is due to impurities present in the material.
• For an opaque material, light may scatter in different directions as it bounces off due to irregularities in the material's shape.
• Shorter wavelengths of visible light are scrattered by nitrogen and oxygen molecules in the atmosphere, making the sky appear blue.
• During sunset, the light coming from the sun hits the atmosphere at a different angle making the sky appear red.
• During a lunar eclipse, the moon will appear to be red in a location where a total lunar eclipse will happen. This reddish appearance of the moon is because of sunlight being scattered by the Earth's atmosphere with the longer wavelength light hitting the moon's surface.
• Diffraction is the spreading0out of light after passing through a narrow slit.
• When the opening is smaller, the diffraction is greater.
• The diffraction is also greater if the wavelength is longer.
• Interference is the overlapping of two or more waves into one wave whenever they pass through the same point
• Destructive interferance


  happens when the opposite parts of two waves meet.
• Destructive interference


  For example, a crest of one wave meets the trough of another wave. This type of interference results in the cancellation of the waves.
• Constructive interference


  happens when identical parts of two waves meet
• Constructive interference


  For example: the crest of one wave meets the crest of another wave of the same wavelength. It creates a bigger wave with the same wavelength but twice the amplitude.
• Thomas Young (1773–1729)


  His double-slit experiment demonstrated that light exhibits interference. The bright fringes are the areas where the waves interfere constructively, whereas the dark fringes are the areas where the waves interfere destructively.