Ask-a-Physicist by Topic
Light & Optics
Assume two photons are moving in opposite directions from each other from a common light source. How fast would they be traveling relative to each other? Twice the speed of light? If the speed of light is the ultimate speed limit in the universe, how can something travel twice that speed?
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If photons have no mass, why is it impossible for them to reach the escape velocity of a black hole? It seems that a massless particle/wave would have no difficulty escaping the gravity of a black hole, no matter how massive the singularity. Find out the answer »
When carrying out the double slit experiment using electrons or buckyball molecules, do the particles have to be traveling at near light speed velocities to produce an interference pattern?
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If you shake the sun, how long would it take before it had an effect on the position of the earth?
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Since the earthquake in Japan the country has been having trouble with their nuclear energy plants and possible meltdown. The question is why aren’t they using lead to absorb the radiation?
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Can you explain why a penny under a glass beaker of water disappears? If you add some water to top of the penny and return it to under the beaker it is visible.
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Explain how beautiful sunrises and sunsets are the result of dust in the atmosphere? Find out the answer »
How is the photoelectric effect used to produce a current in a photovoltaic cell? Find out the answer »
I understand now why the sky is blue, but why are sunsets red and orange? - AB, Oak Ridge, TN Find out the answer »
What happens when you use the tab on an inside rearview mirror to diminish the brightness of the headlights behind you? RC, Vail Colorado Find out the answer »
How does MP3 recording compress digital music by factors near 10? I roughly understand zip encoding, but that usually only reduces file sizes by 2 or less. — J, Greenbelt, MD Find out the answer »
I've heard that digital encoding on audio CDs represents a pressure wave. But audio has so many components like volume, pitch, and timbre; how can the binary encoding of a pressure wave encompass all these attributes? RY, Madison Wisconsin. Find out the answer »
Do bubbles last longer in cold weather or hot weather? Why? — A, Alpharetta, Georgia Find out the answer »
An electron beam, such as the one found in a TV picture tube, is composed of negatively charged electrons. Why is it that this beam does not rapidly spread out owing to the electric repulsion? I realize that the tube has various focusing magnets and such, but I would think the electronic repulsion would be a serious problem. - JT, Buffalo Grove, IL Find out the answer »
We're confused about the difference between fluorescent and halogen bulbs. Fluorescent bulbs are classified as hazardous waste because they contain mercury. Do halogen bulbs also contain mercury? - LR and APM, Washington, DC Find out the answer »
