C. Capacitance. Chapter 18 – Part II. Two parallel flat plates that store CHARGE is called a capacitor. The plates have dimensions >>d, the plate separation. The electric field in a parallel plate capacitor is normal to the plates. The “fringing fields” can be neglected.
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that store CHARGE is
called a capacitor.
The plates have
dimensions >>d, the plate
The electric field in a
parallel plate capacitor
is normal to the plates.
The “fringing fields”
can be neglected.
Actually ANY physical
object that can store charge
is a capacitor.
A Capacitor Stores
Apply a Potential Difference V
And a charge Q is found on the
The capacitor therefore stores energy!
The two metal objects in the figure have net charges of +79 pC and -79 pC, which result in a 10 V potential difference between them.
(a) What is the capacitance of the system? [7.9] pF(b) If the charges are changed to +222 pC and -222 pC, what does the capacitance become? [7.9] pF(c) What does the potential difference become?[28.1] V
C2= 5.3 uf
C3= 4.5 ud
Find the equivalent capacitance between points a and b in the combination of capacitors shown in the figure.
V(ab) same across each
A capacitor is charged by being connected to a battery and is then disconnected from the battery. The plates are then pulled apart a little. How does each of the following quantities change as all this goes on? (a) the electric field between the plates, (b) the charge on the plates, (c) the potential difference across the plates, (d) the total energy stored in the capacitor.
C0 = Vacuum or air Value
C = With dielectric in place
The battery means that the
potential difference across
the capacitor remains constant.
For this case, we insert the dielectric but hold the voltage constant,
since C kC0
THE EXTRA CHARGE COMES FROM THE BATTERY!
Remember – We hold V constant with the battery.
When the dielectric is inserted, no charge
is added so the charge must be the same.
0 2xEsheet 0