To Show the Factors that Affect the Capacitance of a Parallel Plate Capacitor
Van de Graaff generator Parallel plate capacitor
Gold leaf electroscope
Fig 16.6
Theory Since
C r 1 V
,by showing the effect of a factor on voltage,we can conclude it has the reverse effect on capacitance.
We show the effect a factor has on the potential difference between the plates by varying one factor, keeping the other two fixed and observing the effect on the divergence of the leaf in the gold leaf electroscope.
Apparatus Two metal plates,Van de Graaff generator, gold leaf electroscope, leads
Procedure Set up apparatus as illustrated in Fig 16.6. Charge the plates by turning on the Van de Graaff generator. Vary the distance (d) between the plates. Vary the overlap area (A) of overlap. Place different insulators between the plates, thus varying the permittivity ( ) of the dielectric.
e
Observation and Conclusion Increasing d
Increasing A decreasing divergence decreasing V increasing C Increasing decreasing divergence decreasing V increasing C
Q eQ
Q Q Q
Q increasing divergence increasing V decreasing C Q Q
Q
SAMPLE PROBLEM 16C
The plates of a parallel plate capacitor are positioned 2 mm apart in air.The plates are square and both have sides of length 10 cm.The plates fully overlap. The permittivity of air is 8.9 1012 F m1. The permittivity of mica is 6.2 1011 F m1.
