Problem 2.4 Solve the time-independent Schrödinger equation with appropriate boundary conditions for an infinite square well centered at the origin [V (x) = 0, for -a/2 < x < consistent with mine (Equation 2.23), and confirm that your y's can be obtained from mine (Equation 2.24) by the substitution x x - a/2. +a/2; V (x) = 0 otherwise]. Check that your allowed energies are %3|

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A. So the distinct solutions are
kn
with n = 1, 2, 3, ....
[2.22]
a
Curiously, the boundary condition at x = a does not determine the constant A,
but rather the constant k, and hence the possible values of E:
h°k; n?n?h?
En
Griffiths
Introductio
quantum
mechanics
[2.23]
2m
2ma?
In sharp contrast to the classical case, a quantum particle in the infinite square well
cannot have just any old energy-only these special allowed values. Well, how do
we fix the constant A? Answer: We normalize :
14? sin'(kx)dx =|A 1,
а
so |4? =
= -.
a
This only determines the magnitude of A, but it is simplest to pick the positive real
root: A = /2/a (the phase of A carries no physical significance anyway). Inside the
well, then, the solutions are
2020
You moved an ite
NT
Griffithe
Vn(x) = .
- sin
[2.24]
a
a
As promised, the time-independent Schrödinger equation has delivered an infi-
nite set of solutions, one for each integer n. The first few of these are plotted in Fig-
ure 2.2; they look just like the standing waves on a string of length a. 1, which car-
ries the lowest energy, is called the ground state; the others, whose energies increase
Pepeojdn noA
Giffiths
roun the functions lk (r) have
Transcribed Image Text:A. So the distinct solutions are kn with n = 1, 2, 3, .... [2.22] a Curiously, the boundary condition at x = a does not determine the constant A, but rather the constant k, and hence the possible values of E: h°k; n?n?h? En Griffiths Introductio quantum mechanics [2.23] 2m 2ma? In sharp contrast to the classical case, a quantum particle in the infinite square well cannot have just any old energy-only these special allowed values. Well, how do we fix the constant A? Answer: We normalize : 14? sin'(kx)dx =|A 1, а so |4? = = -. a This only determines the magnitude of A, but it is simplest to pick the positive real root: A = /2/a (the phase of A carries no physical significance anyway). Inside the well, then, the solutions are 2020 You moved an ite NT Griffithe Vn(x) = . - sin [2.24] a a As promised, the time-independent Schrödinger equation has delivered an infi- nite set of solutions, one for each integer n. The first few of these are plotted in Fig- ure 2.2; they look just like the standing waves on a string of length a. 1, which car- ries the lowest energy, is called the ground state; the others, whose energies increase Pepeojdn noA Giffiths roun the functions lk (r) have
conditions.)
Problem 2.4 Solve the time-independent Schrödinger equation with appropriate
boundary conditions for an infinite square well centered at the origin [V (x) = 0, for
-a/2 < x < +a/2; V (x) = ∞ otherwise]. Check that your allowed energies are
consistent with mine (Equation 2.23), and confirm that your y's can be obtained from
mine (Equation 2.24) by the substitution x x - a/2.
Droblo m 25 Celaulnte lu)
.2
Transcribed Image Text:conditions.) Problem 2.4 Solve the time-independent Schrödinger equation with appropriate boundary conditions for an infinite square well centered at the origin [V (x) = 0, for -a/2 < x < +a/2; V (x) = ∞ otherwise]. Check that your allowed energies are consistent with mine (Equation 2.23), and confirm that your y's can be obtained from mine (Equation 2.24) by the substitution x x - a/2. Droblo m 25 Celaulnte lu) .2
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