Archives of Ask A Scientist!
About "Ask A Scientist!"
On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.
Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.
The light produced by most lamps, and by the sun, contains all visible colors, and is perceived as white. When an object is illuminated by white light, it may be reflected, transmitted, or absorbed. It is the wavelengths of the reflected and transmitted light that determine the color that we perceive. For example, the leaves of most plants absorb red and blue light very strongly and reflect green light efficiently. Carrots, on the other hand, absorb blue and green light and reflect yellow, orange and red light. So we perceive leaves to be green and carrots as orange. The exact shades of the colors that we observe depend upon the precise wavelengths that are absorbed. Smooth and rough surfaces reflect light differently, making some objects appear shiny and others dull.
Most objects are made up of molecules, which in turn consist of individual atoms held together by electrons. It is the electrons in atoms and molecules that are responsible for the absorption of light. For example, when the molecule chlorophyll in plants absorbs blue or red light, an electron is excited from a low energy state to a higher energy state. The energy difference between the two states must be exactly equal to the energy of the absorbed light. In the case of chlorophyll, the energy gaps between the lower and higher energy states correspond to light that appears either red or blue to our eye, and the unabsorbed green light is reflected. On the other hand, the energy of light absorbed by electrons in carotene, the molecule responsible for the color of carrots, corresponds to wavelengths perceived as blue and green, and orange and red light is reflected. The carbon in charcoal or in a pencil absorbs all visible colors. Very little visible light is reflected, so these materials appear black. White paper and white cloth do not absorb visible wavelengths, but instead reflect all of them.
Highly colored molecules that absorb at certain wavelengths, known as dyes and pigments, have been used for thousands of years to add color to materials. While chlorophyll is a common pigment easily extracted from plants, it isn't commonly used for coloring clothes because it is somewhat soluble in soapy water. That fact will be useful to people who get grass stains on their clothes!
- Are cats and dogs colorblind? Do cats' eyes glow in the dark?
- Why do stars twinkle?
- Why does oil float above water?
- Why do drops of water cling to glass?
- What causes a heat sensitive material, such as a mood ring, to change color when it's temperate is altered? What is this material made of, and where else might it be used?
- When a water surface reflects something (when looking from the top), does it undergo total internal reflection?
- Why can't you put metal in a microwave?
- If the electrons are attracted to the protons, why don't they come crashing into the nucleus?
- How do CDs Work?
- How much progress are scientists making in finding an enzyme that will degrade plastic to something environmentally friendly that can be safely reintroduced to the earth around us?