EE Pro for TI - 89, 92 Plus
Equations - Capacitors & Electric Fields
19
Solution -
After examining the problem, all the three equations need to be selected to solve the
problem. Press
„
to display the input variable screen. Enter all the known variables, and press
„
to
solve the selected equation set. The computed results are shown in the screen display below.
Input Values for the example
Computed results
-PQYP8CTKCDNGUTC
AEO
TD
AEO
ε
T
T
AEO
ρ
N
'AEQWNQODUO
%QORWVGF4GUWNVUEN
'A(O
'T
A8OCPF
8
A8
17.7 Sphere
The first equation in this topic computes the potential between two concentric spheres of radius ra and rb, with a
charge Q, and separated by a medium with a relative permittivity of
ε
r. The second equation computes the electric
field outside a sphere at a distance r from the center of the sphere. The last equation computes the capacitance
between the spheres.
V
Q
r
ra
rb
=
⋅ ⋅ ⋅
⋅
−
F
HG
I
KJ
4
0
1
1
π ε ε
Eq. 17.7.1
Er
Q
r r
=
⋅ ⋅ ⋅ ⋅
4
0
2
π ε ε
Eq. 17.7.2
C
r ra rb
rb
ra
= ⋅ ⋅ ⋅ ⋅ ⋅
−
4
0
π ε ε
Eq. 17.7.3
Example 17.7 -
Two concentric spheres 2_cm and 2.5_cm radius, are separated with a dielectric with a relative
permittivity of 1.25. The inner sphere has a charge of 1.45E-14_coulombs. Find the potential difference between
the two spherical plates of the capacitor as well as the capacitance.
Entered Values
Computed results
Solution - Upon examining the problem, equations 17.7.1 and 17.7.3 are needed to compute a solution.
Select these by highlighting each equation and pressing the
¸
key. Press
„
to display the input