AAMC Sample Test Physical Sciences Question 52

[premed_noob]

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I had a quick question regarding the AAMC Official MCAT Sample Test Question 52 in Physical Sciences (Passage 10)

In order to find out the frequency we obviously need to have Planck's Constant memorized. The energy of the photon is given in keV instead of Joules and we need to be able to convert that to Joules in order to answer the question. Having to memorize 1.6 x 10^-16 J = 1 keV seems really tedious to me. But I guess that is something we need to memorize? Is there a simpler way to do this problem?

Q52: What is the frequency of the emitted gamma photon?

All the passage gives is that it's a 140 keV gamma photon.

 

[NextStepTutor_3]

Personally (and I'd love to hear what others say about this) I don't think the AAMC actually wants you to do the math here, and I certainly believe that knowing the conversion isn't necessary. I don't have the test pulled up now, but the answer choices are REALLY far apart - like 16 orders of magnitude or more. First of all, we know that gamma rays are higher-frequency than visible light, and we CAN calculate the approximate frequency of visible light using easy numbers that we already know (I used 3x10^8 for the speed of light and 4oo nm for the wavelength, though of course we could use any vale between 400 and 700 nm). We find that visible light has a frequency somewhere on the order of 10^15.

This immediately eliminates the two answers that have negative exponents (and that would be a ridiculously tiny frequency anyway). So we're left between the correct answer and one other, which has an absurdly high frequency. The only logical choice is the correct one.