A capacitor is made from two hollow, coaxial, iron cylinders, one inside the oth
ID: 778406 • Letter: A
Question
A capacitor is made from two hollow, coaxial, iron cylinders, one inside the other. The inner cylinder is negatively charged and the outer is positively charged; the magnitude of the charge on each is 18.0 pC . The inner cylinder has a radius of 0.450 mm , the outer one has a radius of 5.00 mm , and the length of each cylinder is 12.0 cm .
(a)What is the capacitance?
Use 8.854×1012 F/m for the permittivity of free space.
(b)What applied potential difference is necessary to produce these charges on the cylinders?
Explanation / Answer
given
L = 12 cm = 0.12 m
a = 0.45 mm
b = 5 mm
a)
Capacitnace of a cyllidrical capacitor, C = 2*pi*epsilon*L/ln(b/a)
= 2*pi*8.854*10^-12*0.12/ln(5/0.45)
= 2.77*10^-12 F or 2.77 pF
b) we know, Q = C*V
==> V = Q/C
= 18*10^-12/(2.77*10^-12)
= 6.50 V
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