Sci10 The Facts of Light PDF

Tanay West, Education at its Best! The Facts of Light SCIENCE 10  OPTICS A branch of physics that studies the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it.  Facts of Light ❑...

Tanay West, Education at its Best! The Facts of Light SCIENCE 10  OPTICS A branch of physics that studies the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it.  Facts of Light ❑ Light is very common that we often take it for granted. Yet the world would quickly change if suddenly there is no light. ❑ People have found ways of making and controlling light to see when there is no sunlight. At first, they produced light with campfires and torches. Later, they developed candles, oil lamps, gas lights, and electric lights. ❑ There were two theories on the basic nature of light. The first theory was the Wave (Undulatory) Theory. ❑ One of the proponents of the wave theory was Christian Huygens (1629 - 1695), who explained the wave fronts at right angles to the path of the rays. ❑ This theory explains that light has a wave motion that starts from a vibrating body and is transmitted at high speed. ❑ Since light can pass through a vacuum, he explained that light may travel through a medium known as “ether”, a mysterious substance which is not air. ❑ In 1704, Sir Isaac Newton contradicted the Wave Theory as he described light as a stream of particles or corpuscles. ❑ This theory known as the Corpuscular or Emission Theory, light consists of tiny particles of matter emitted by a source that travel only in straight lines called rays.  Speed of Light ❑ The speed with which light (or radiant energy) travels through space is one of the precisely measured quantities in physical sciences. ❑ Galileo Galilei was the first to hypothesize that light had a finite speed, however, there is no way to prove his theory in his lifetime. ❑ In 1675, Ole Roemer, a Danish astronomer became the first to measure the speed of light over an astronomical distance. ❑ However, the currently accepted value for the speed of light in empty space as 2.9979 x 108 m/s was determined through the experiments conducted by physicist Albert A. Michelson, for which he became the first American to receive the Nobel Prize in Science.  Sources of Light ❑ All light must come from a source. Luminous objects are objects that emit or send off their own light. They tend to radiate heat as an effect of being luminous and can store energy. ✓ Can you name some sources of light? Sources of Light ❑ Non-luminous objects, on the other hand, are those that cannot emit their own light. For us to see them, a light from luminous object must be reflected. How light is produced? ❑ Light is produced through incandescence and luminescence. ❑ When an object is heated at a very high temperature, say about 470°C, it starts to glow and become dull red in color. We call this incandescence. ❑ The high temperature causes the atoms to vibrate and give off energy in the form of EM radiation. ❑ The sun gives off both heat and light as a result of nuclear reactions in its core. An incandescent light bulb gives off light when a wire filament inside the bulb is heated to white heat. ❑ The term luminescence is used to describe a process by which light is produced other than by heating. Two forms of luminescence can be identified, depending on the amount of time emitted light continues to glow. ❑ Fluorescence refers to the release of light that lasts no more than about 10 nanoseconds after it begins (example: fluorescent light bulb). ❑ Phosphorescence refers to the release of light that lasts longer than 10 nanoseconds. ❑ Phosphorescent materials are used in glow-in-the-dark objects. Light and Transparency ❑ Objects can be classified in terms of the way they allow light to pass through them. ✓ Transparent ✓ Opaque ✓ Translucent ❑ Transparent materials such as air, glass, water, and clear plastic permit the passage of light. ❑ Opaque are materials that block off the light. Examples are woods, concretes, metals, and flesh of some animals. ❑ There are also objects that allow only some amount of light to pass through and are called translucent materials. These materials have both the characteristics of opaque and transparent materials. ❑ Shadows formed by opaque materials may or may not be sharp depending on the size of the source used to illuminate the object.  Brightness of Light ❑ Photometry is a branch of optics that deals with the illumination and the amount of brightness that a light source possesses. ❑ Luminous intensity refers to the brightness of a light source. It is expressed in the unit candela (cd). ❑ The luminous energy emitted from a light source is called luminous flux and is expressed in lumens (lm).