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Problem
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\prob{28}
A system is known to be in the normalized state described by the wave function
$\psi(\theta,\psi)=\frac{1}{\sqrt{30}}(5Y^3_4+Y^3_6-2Y^0_6$,
where the $Y^m_l(\theta,\phi)$ are the spherical harmonics. The probability of finding the system in a state with azimuthal orbital quantum number m=3 is

  1. 0
  2. 1/15
  3. 1/6
  4. 1/3
  5. 13/15

Quantum Mechanics}Probability

One doesn't actually need to know much (if anything) about spherical harmonics to solve this problem. One needs only the relation P=\sum_i |\langle Y^3_i |\psi (\theta,\phi)\rangle|^2. Since the problem asks for states where m=3, and it gives the form of spherical harmonics employed as Y^m_l, one can eliminate the third term after the dot-product.

So, the given wave function \psi(\theta,\psi)=\frac{1}{\sqrt{30}}\left( 5 Y^3_4 + Y^3_6 - 2Y^0_6\right) gets dot-product'ed like |\langle Y^3_i |\psi (\theta,\phi)\rangle|^2\left(\frac{1}{\sqrt{30}}\left( 5 Y^3_4 + Y^3_6\right)\right)\left(\frac{1}{\sqrt{30}}\left( 5 Y^3_4 + Y^3_6 - 2Y^0_6\right)\right)=\frac{25+1}{30}=\frac{13}{15}, as in choice (E).

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Comments
mpdude8
2012-04-19 19:55:26
One can also deduce that the particle is more likely than not to have m = 5 by looking at the normalized wave function. E is the only possibility that fits.NEC
tera
2006-08-21 04:37:41
No dirac symbols not anything. The Possibility is c1^2 + c2^2 as ina a simple mathematical problem in our case 25/30+1/30=26/30
jmason86
2009-09-09 22:12:22
agreed, the probability of finding a system in a given state is always just the sum of the squares of the coefficients in the wavefunction.
NEC

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One can also deduce that the particle is more likely than not to have m = 5 by looking at the normalized wave function. E is the only possibility that fits.

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