State Examination Commission – Physics Higher Level, 2006
Question 12b
List the factors that affect the capacitance of a parallel plate capacitor.
(6)
The plates of an air filled parallel plate capacitor have a common area of 40 cm2 and are 1 cm apart. The capacitor is
connected to a 12 V d.c. supply.
Calculate
(i) the capacitance of the capacitor;
(ii) the magnitude of the charge on each plate.
(15)
What is the net charge on the capacitor?
Give a use for a capacitor.
(7)
(permittivity of free space = 8.85 × 10–12 F m–1)
_______________________________________________
List the factors that affect the capacitance of a parallel plate capacitor.
(6)
The factors are
i. common area of plates
ii. distance plates are separated
iii. dielectric between plates
The plates of an air filled parallel plate capacitor have a common area of 40 cm2 and are 1 cm apart. The capacitor is
connected to a 12 V d.c. supply.
Calculate
(i) the capacitance of the capacitor;
C
=
=
=
εA/d
(8.85 × 10–12)(0.004)/(0.01)
3.5 × 10–12 F
(ii) the magnitude of the charge on each plate.
C
Q
=
=
Q/V
CV
=
3.5 × 10–12 × 12
(15)
=
4.2 × 10–11 C
What is the net charge on the capacitor?
Net charge
=
OC
(equal but opposite charges on each plate)
Give a use for a capacitor.
(7)
Capacitors are used to convert a.c. to d.c.
C. Garvey 2006