9. Quantum Mechanics
Speed of Light
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In this example, it says to calculate the frequency of the red light emitted by a neon sign with a wavelength of 663.8 nanometers. Alright. So we need to determine what our frequency is, which is mu. They're giving us our wavelength which is lambda. Remember the equation that connects them together is that the speed of light equals them multiplying one another. Now remember, wavelength needs to be in units of meters. So we need to do a metric prefix conversion where we have 663.8 nanometers, and we're gonna say here that for every 1 nanometer it's 10 to the negative 9 meters. So here, meters will come out to be 6.638 times 10 to the negative 7 meters. Now that we have that, we can plug it in. We have the speed of light. We have we're looking for our frequency. We have our wavelength in meters. So divide both sides now by meters. So when we do that, we're gonna get left at the end our seconds inverse. So here we're gonna say frequency equals 4 point 519 times 10 to the 14 seconds inverse. Because remember, meters cancel out here, so we're left with 1 over seconds, seconds, which is the same thing as seconds inverse. Okay. So your units can be either 1 over seconds or seconds inverse or hertz. All of them mean the same thing. And here our answer has 4 sig figs because our wavelength was given to us also within 4 sig figs.
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