Material That Absorbs Light Energy

Light Assimilation, Reflection, and Transmission

Nosotros accept previously learned that visible light waves consist of a continuous range of wavelengths or frequencies. When a calorie-free wave with a unmarried frequency strikes an object, a number of things could happen. The light wave could be absorbed by the object, in which case its energy is converted to heat. The light wave could be reflected by the object. And the lite wave could be transmitted by the object. Rarely however does just a single frequency of light strike an object. While it does happen, it is more usual that visible light of many frequencies or even all frequencies is incident towards the surface of objects. When this occurs, objects have a tendency to selectively absorb, reflect or transmit light certain frequencies. That is, one object might reverberate green lite while absorbing all other frequencies of visible light. Another object might selectively transmit blue calorie-free while absorbing all other frequencies of visible lite. The manner in which visible light interacts with an object is dependent upon the frequency of the light and the nature of the atoms of the object. In this section of Lesson 2 we volition discuss how and why light of certain frequencies tin can exist selectively absorbed, reflected or transmitted.

Visible Light Assimilation

Atoms and molecules comprise electrons. It is often useful to think of these electrons every bit beingness attached to the atoms by springs. The electrons and their attached springs have a trend to vibrate at specific frequencies. Like to a tuning fork or even a musical instrument, the electrons of atoms have a natural frequency at which they tend to vibrate. When a lite wave with that same natural frequency impinges upon an cantlet, then the electrons of that atom volition exist set into vibrational move. (This is only some other example of the resonance principle introduced in Unit eleven of The Physics Classroom Tutorial.) If a light moving ridge of a given frequency strikes a cloth with electrons having the same vibrational frequencies, then those electrons will blot the energy of the light wave and transform it into vibrational motion. During its vibration, the electrons interact with neighboring atoms in such a manner as to catechumen its vibrational free energy into thermal free energy. After, the light wave with that given frequency is absorbed by the object, never again to exist released in the form of lite. So the selective absorption of light by a detail material occurs because the selected frequency of the light wave matches the frequency at which electrons in the atoms of that material vibrate. Since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies of visible light.

Visible Light Reflection and Transmission

Reflection and transmission of low-cal waves occur considering the frequencies of the calorie-free waves do not match the natural frequencies of vibration of the objects. When low-cal waves of these frequencies strike an object, the electrons in the atoms of the object begin vibrating. But instead of vibrating in resonance at a big amplitude, the electrons vibrate for brief periods of fourth dimension with small amplitudes of vibration; then the energy is reemitted as a light wave. If the object is transparent, then the vibrations of the electrons are passed on to neighboring atoms through the majority of the cloth and reemitted on the reverse side of the object. Such frequencies of low-cal waves are said to be transmitted . If the object is opaque, and then the vibrations of the electrons are not passed from atom to atom through the bulk of the cloth. Rather the electrons of atoms on the material's surface vibrate for short periods of time and then reemit the energy as a reflected light wave. Such frequencies of low-cal are said to be reflected .

Where Does Color Come From?

The color of the objects that we meet is largely due to the mode those objects interact with light and ultimately reflect or transmit it to our eyes. The color of an object is not actually inside the object itself. Rather, the color is in the light that shines upon it and is ultimately reflected or transmitted to our eyes. Nosotros know that the visible light spectrum consists of a range of frequencies, each of which corresponds to a specific color. When visible light strikes an object and a specific frequency becomes absorbed, that frequency of light will never make information technology to our eyes. Any visible light that strikes the object and becomes reflected or transmitted to our optics volition contribute to the color appearance of that object. Then the color is not in the object itself, merely in the light that strikes the object and ultimately reaches our centre. The but part that the object plays is that it might incorporate atoms capable of selectively arresting ane or more than frequencies of the visible light that shine upon information technology. So if an object absorbs all of the frequencies of visible low-cal except for the frequency associated with greenish light, and so the object will announced dark-green in the presence of ROYGBIV. And if an object absorbs all of the frequencies of visible low-cal except for the frequency associated with blue light, so the object volition appear blue in the presence of ROYGBIV.

Consider the two diagrams beneath. The diagrams depict a sheet of newspaper being illuminated with white lite (ROYGBIV). The papers are impregnated with a chemical capable of absorbing one or more of the colors of white light. Such chemicals that are capable of selectively absorbing 1 or more than frequency of white light are known as pigments . In Case A, the pigment in the canvass of paper is capable of absorbing ruby-red, orange, yellow, blue, indigo and violet. In Case B, the pigment in the canvass of paper is capable of absorbing orange, yellow, green, blue, indigo and violet. In each instance, whatever color is not absorbed is reflected.

Check your understanding of these principles by determining which color(s) of lite are reflected by the paper and what colour the newspaper volition announced to an observer.

Transparent materials are materials that let one or more of the frequencies of visible lite to be transmitted through them; whatever color(due south) is/are not transmitted by such objects, are typically absorbed by them. The appearance of a transparent object is dependent upon what color(s) of light is/are incident upon the object and what color(s) of low-cal is/are transmitted through the object.

Express your understanding of this principle by filling in the blanks in the following diagrams.

The colors perceived of objects are the results of interactions between the various frequencies of visible calorie-free waves and the atoms of the materials that objects are fabricated of. Many objects comprise atoms capable of either selectively absorbing, reflecting or transmitting one or more frequencies of calorie-free. The frequencies of light that become transmitted or reflected to our eyes will contribute to the colour that nosotros perceive.

We Would Like to Advise ...

Sometimes information technology isn't enough to just read almost it. You take to interact with it! And that's exactly what yous practice when you use 1 of The Physics Classroom'southward Interactives. Nosotros would like to propose that you combine the reading of this folio with the use of our Stage Lighting Interactive. The Interactive is found in the Physics Interactives section of our website and allows a learner to explore the advent of actors upon the stage when illuminated with varying combinations of red, green, and blue light.

Check Your Agreement

1. Natural philosophers have long pondered the underlying reasons for color in nature. One mutual historical belief was that colored objects in nature produce small particles (perhaps light particles) that afterwards attain our eyes. Different objects produce different colored particles, thus contributing to their different appearance. Is this belief authentic or not? __________________ Justify your respond.

2. What colour does a red shirt appear when the room lights are turned off and the room is entirely dark? ____________ What about a blue shirt? ____________ ... a green shirt? ____________

3. The diagrams describe a sheet of paper beingness illuminated with white light (ROYGBIV). The papers are impregnated with a chemical capable of absorbing one or more than of the colors of white light. In each case, make up one's mind which colour(s) of light are reflected by the paper and what color the paper will appear to an observer.

four. The appearance of a transparent object is dependent upon which color(s) of light is/are incident upon the object and which colour(s) of calorie-free is/are transmitted through the object. Express your understanding of this principle past determining which colour(s) of light volition be transmitted and the color that the paper will announced to an observer.