phy-4600/solutions/chap7/prob8
2016-03-25 20:08:04 -04:00

135 lines
3.9 KiB
Plaintext
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

7.35 is nothing more than a definition of spherical coordinates.
⎧ x = r sinθ cosϕ
⎨ y = r sinθ sinϕ
⎩ z = r cosθ
Some differential forms may come in handy.
∂/∂θ:
⎧ ∂x = r cosϕ cosθ ∂θ
⎨ ∂y = r sinϕ cosθ ∂θ
⎩ ∂z = - r sinθ ∂θ
∂/∂ϕ:
⎧ ∂x = - r sinθ sinϕ ∂ϕ
⎨ ∂y = r sinθ cosϕ ∂ϕ
⎩ ∂z = 0 ∂ϕ
7.47 is the set of algebraic conditions expressed by the vector definition 𝐋 = 𝐫 × 𝐩.
⎧ L̂𝓍 = yp𝓏 - zp𝓎 = -ιħ (y ∂͟_ - z ∂͟_ )
⎪ ∂z ∂y
⎨ L̂𝓎 = zp𝓍 - xp𝓏 = -ιħ (z ∂͟_ - x ∂͟_ )
⎪ ∂x ∂z
⎪ L̂𝓏 = xp𝓎 - yp𝓍 = -ιħ (x ∂͟_ - y ∂͟_ )
⎩ ∂y ∂x
Substituting 7.35 into 7.47,
⎧ L̂𝓍 = -ιħ (r sinθ sinϕ ∂͟_ - r cosθ ∂͟_ )
⎪ ∂z ∂y
⎨ L̂𝓎 = -ιħ (r cosθ ∂͟_ - r sinθ cosϕ ∂͟_ )
⎪ ∂x ∂z
⎪ L̂𝓏 = -ιħ (r sinθ cosϕ ∂͟_ - r sinθ sinϕ ∂͟_ )
⎩ ∂y ∂x
Geometry is shown on the attached notes page.
For L̂𝓍:
∂͟z͟ = -r sinθ
∂θ
∂͟y͟ = r sinθ cosϕ
∂ϕ
𝓍 = -ιħ ( r sinθ sinϕ ∂͟θ͟ ∂͟_ - r cosθ ∂͟ϕ͟ ∂͟_ )
∂θ ∂z ∂ϕ ∂y
𝓍 = ιħ ( -r sinθ sinϕ ∂͟θ͟ ∂͟_ + r cosθ ∂͟ϕ͟ ∂͟_ )
∂z ∂θ ∂y ∂ϕ
𝓍 = ιħ ( ͟r͟ s͟i͟n͟θ͟ sinϕ ∂͟_ + c͟o͟s͟θ͟ ∂͟_ )
-r sinθ ∂θ sinθ cosϕ ∂ϕ
𝓍 = ιħ ( sinϕ ∂͟_ + c͟o͟t͟θ͟ ∂͟_ )
∂θ cosϕ ∂ϕ
For L̂𝓎:
∂x = r cosϕ cosθ ∂θ
∂z = 0 ∂ϕ
𝓎 = -ιħ (r cosθ ∂͟_ - r sinθ cosϕ ∂͟_ )
∂x ∂z
𝓎 = ιħ (-r cosθ ∂͟θ͟ ∂͟_ + r sinθ cosϕ ∂͟ϕ͟ ∂͟_ )
∂θ ∂x ∂ϕ ∂z
𝓎 = ιħ (-r cosθ ∂͟θ͟ ∂͟_ + r sinθ cosϕ ∂͟ϕ͟ ∂͟_ )
∂x ∂θ ∂z ∂ϕ
𝓎 = ιħ (- _͟1͟ cosθ ∂͟_ + r sinθ cosϕ 0 ∂͟_ )
cosϕ cosθ ∂θ ∂ϕ
𝓎 = ιħ (- _͟1͟ ∂͟_ )
cosϕ ∂θ
𝓎 = -ιħ _͟1͟ ∂͟_
cosϕ ∂θ
For L̂𝓏:
∂x = -r sinθ sinϕ ∂ϕ
∂y = r sinθ cosϕ ∂ϕ
𝓏 = -ιħ (r sinθ cosϕ ∂͟͟ϕ͟ ∂͟_ - r sinθ sinϕ ∂͟͟ϕ͟ ∂͟_ )
∂ϕ ∂y ∂ϕ ∂x
𝓏 = -ιħ (r͟ s͟i͟n͟θ͟ c͟o͟s͟ϕ͟ ∂͟_ + r͟ s͟i͟n͟θ͟ s͟i͟n͟ϕ͟ ∂͟_ )
r sinθ cosϕ ∂ϕ r sinθ sinϕ ∂ϕ
𝓏 = -ιħ ∂͟_ ( 1 + 1 )
∂ϕ
𝓏 = -2ιħ ∂͟_
∂ϕ
So, according to my calculus, the final solutions should be the set
⎧ L̂𝓍 = ιħ ( sinϕ ∂͟_ + c͟o͟t͟θ͟ ∂͟_ )
⎪ ∂θ cosϕ ∂ϕ
⎨ L̂𝓎 = -ιħ _͟1͟ ∂͟_
⎪ cosϕ ∂θ
⎪ L̂𝓏 = -2ιħ ∂͟_
⎩ ∂ϕ
The spherical representation, i.e. ending place, is the set
⎧ L̂𝓍 = ιħ (sinϕ ∂͟_ + cosϕ cotθ ∂͟_ )
⎪ ∂θ ∂ϕ
⎨ L̂𝓎 = ιħ (-cosϕ ∂͟_ + sinϕ cotθ ∂͟_ )
⎪ ∂θ ∂ϕ
⎪ L̂𝓏 = -ιħ ∂͟_
⎩ ∂ϕ
My set DOES NOT match this. I must be going about this the wrong way. I have to give it more thought. Perhaps a purely geometric approach will improve my answers: I'll try that over the weekend.