boylistad

426 ⏐⏐⏐ CAPACITORS
PROBLEMS
SECTION 10.2 The Electric Field
1. Find the electric field strength at a point 2 m from a
charge of 4 mC.
2. The electric field strength is 36 newtons/coulomb (N/C)
at a point r meters from a charge of 0.064 mC. Find the
distance r.
SECTION 10.3 Capacitance
3. Find the capacitance of a parallel plate capacitor if
1400 mC of charge are deposited on its plates when 20 V
are applied across the plates.
4. How much charge is deposited on the plates of a 0.05-mF
capacitor if 45 V are applied across the capacitor?
5. Find the electric field strength between the plates of a
parallel plate capacitor if 100 mV are applied across the
plates and the plates are 2 mm apart.
6. Repeat Problem 5 if the plates are separated by 4 mils.
7. A 4-mF parallel plate capacitor has 160 mC of charge on
its plates. If the plates are 5 mm apart, find the electric
field strength between the plates.
8. Find the capacitance of a parallel plate capacitor if the
area of each plate is 0.075 m 2 and the distance between
the plates is 1.77 mm. The dielectric is air.
9. Repeat Problem 8 if the dielectric is paraffin-coated paper.
10. Find the distance in mils between the plates of a 2-mF
capacitor if the area of each plate is 0.09 m 2 and the
dielectric is transformer oil.
11. The capacitance of a capacitor with a dielectric of air is
1200 pF. When a dielectric is inserted between the plates,
the capacitance increases to 0.006 mF. Of what material
is the dielectric made?
12. The plates of a parallel plate air capacitor are 0.2 mm
apart and have an area of 0.08 m 2 , and 200 V are applied
across the plates.
a. Determine the capacitance.
b. Find the electric field intensity between the plates.
c. Find the charge on each plate if the dielectric is air.
13. A sheet of Bakelite 0.2 mm thick having an area of
0.08 m 2 is inserted between the plates of Problem 12.
a. Find the electric field strength between the plates.
b. Determine the charge on each plate.
c. Determine the capacitance.
SECTION 10.4 Dielectric Strength
14. Find the maximum voltage ratings of the capacitors of
Problems 12 and 13 assuming a linear relationship
between the breakdown voltage and the thickness of the
dielectric.
15. Find the maximum voltage that can be applied across a
parallel plate capacitor of 0.006 mF. The area of one plate
is 0.02 m 2 and the dielectric is mica. Assume a linear
relationship between the dielectric strength and the thickness
of the dielectric.