Midterm Question 6 part A

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Midterm Question 6 part A

Postby 805132275 » Wed Dec 05, 2018 8:20 pm

"Microwave ovens heat food by exciting water to a higher vibration mode....... What is the energy and wavelength of this radiation?"
For this question, I used the Einstein equation to solve for the energy and got it correct; however, looking back to review, I recall being told that that equation was only applicable for energy of a photon. Does the radiation given off by a microwave count as a photon? And in general, which equations are ONLY to be used for light as opposed to electron energy?

Julia Go 2L
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Re: Midterm Question 6 part A

Postby Julia Go 2L » Wed Dec 05, 2018 8:37 pm

You can use equations such as E = h ν, E = hc/ λ and c = λ ν ONLY for light.

De Broglie's equation: λ = h/mv can be used when the object has mass. Microscopic objects like electrons have wavelike properties since it has momentum and mass.

HOWEVER, light does not have mass so you cannot use De Broglie's equation. Microwave ovens emit electromagnetic radiation, which is light and has no mass. So, you were correct to use the equation:
E = hv (note that v = frequency of radiation (NOT velocity) )

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