Engineering Homework
Note that Polystyrene has a dielectric strength of 24 kV/mm and a relative permittivity of 2.6. Mica has a dielectric strength of 40 kV/mm and a relative permittivity of 5.5.
Problem 1: The charge on a 50 -μF capacitor is 10 mC. What is the voltage across the capacitor?
Problem 2: A 10- μF parallel-plate capacitor must be made. It is desired that the dielectric be mica. The capacitor is to be used in a circuit in which it will be charged to 20 V; thus for safety, the capacitor ought to be disigned to have a breakdown voltage of 40 V.
(A) How thick must the mica be?
(B) Given the thickness of the mica, how large must the plates of the capacitor be?
(C) If the mica in the 10- μF capacitor is replaced with polystyrene without changing any of the dimensions of the capacitor, what with the new capacitance value be?
(D) If the mica is replaced with polystyrene, but the dimensions from (A) and (B) are used, what will the capacitors breakdown voltage be? Is it still safe to operate the capacitor at 20 V?
Problem 3: Suppose a parallel-plate capacitor is to be made from two plates with area 0:001935 m2.
(A) What is the capacitance value if the dielectric is a piece of mica that is 470 m thick?
(B) What is the capacitor's breakdown volatage if the dielectric is a piece of mica that is 470 μm thick?
(C) If polystyrene is used as a dielectric instead of mica, what is the thickness of polystyrene required to maintain a breakdown voltage as calculated in (B)?
(D) What is the capacitance value for the polystyrene-based capacitor discussed in (C)?