210 3 Quantum Mechanics – II
∇^2 =
d^2
dr^2
+
(
2
r
)
d
dr
(2)
Inserting (2) in (1) and performing the integration we get
<T>=
^2
2 ma 02
Buta 0 =
2
me^2
Or
2
m=a^0 e
2
Therefore,<T>= e
2
2 a 0
Also<E>=<T>+<V>=e
2
2 a 0 −
e^2
a 0 =−e
(^2) / 2 a 0
3.65 The normalized eigen function for the ground state of hydrogen atom is
ψ 0 = 1 /
(
πa^30
)^12
e−r/a^0
wherea 0 is the Bohr’s radius
(a) The probability that the electron will be formed in the volume element dτ
is
p(r)dr=|ψ 0 |^2 dτ=
(
e
−a^2 r 0
πa^30
)
. 4 πr^2 dr
=
(
4
a 03
)
r^2 e−^2 r/a^0 dr
Maximum probability is found by settingddpr= 0
d
dr
(
4 r^2 e−
(^2) ar
0
a 03
)
=
(
8 r
a^30
)
e−
(^2) ar
0
(
1 −
r
a 0
)
= 0
Thereforer=a 0
(b)<r>=
∫∞
0
ψ∗rψdτ=
1
π
a^30
∫∞
0
rexp
(
−
2 r
a 0
)
. 4 πr^2 dr
=
(
4
a 03
)∫∞
0
r^3 exp
(
−
2 r
a 0
)
dr
Let
2 r
a 0
=x;dr=
a 0 dx
2
<r>=
(a
0
4
)∫∞
0
x^3 e−xdx=
(a
0
4
)
3!=
3 a 0
2
3.66
∫
u^2210 dτ=A 22
∫
e−^2 xx^2 cos^2 θr^2 sinθdθdrdφ
=
(
1
π
)(
1
2 a 0
) 3 ∫∞
0
exp
(
−
r
a 0
)(
r^2
4 a 02
)
r^2 dr
∫+ 1
− 1
cos^2 θd(cosθ)
∫ 2 π
0
dφ
where we have putx=r/ 2 a 0. Putr/a 0 =y,dr=a 0 dy