
A capacitor consists of two _______ or ______ of any shape. The conductors have charges of equal _______ and opposite ______ (__), and a _________ ________ (__) between them. Net charge on a capacitor is ______. When we talk about the charge on a capacitor, we always mean the magnitude of charge on either plate which is + Q. We say that the capacitor stores ______.
 conductors or electrodes
 equal magnitude
 opposite sign (Q)
 potential difference (ΔV)
 zero
 charge

In a capacitor, the electric field strength E and the potential difference ΔV_{C} _______ as the charge on each electrode ________. Define the capacitance, C and state the identity
 increases
 increases
 Capacitance, C: The capacitance of a capacitor is the ratio of the magnitude of the charge on either conductor to the potential difference between the conductors
 C Ξ Q/ΔV > 0

In a capacitor, when a SMALL amount of +charge is moved from one _____ to the other, the electric field and potential difference ΔV are _____. When MORE charge is moved from one ______ to another, the electric field and potential difference _______
 electrode or conductor
 small
 electrode or conductor
 increase

Capacitance is always _______. The SI unit of capacitance is a ______ (__). Typically you will see units of ________ (__) and _______ (__).
The capacitance of a device depends on the ________ arrangement of the conductors:
♜______, _____, and _______ of the two electrodes
♜ A capacitor with a ______ ______ holds more charge for a given potential difference than one with _______ _______
 always positive
 farad (F)
 microfarads (μF) and picofarads (pF)
 geometric
 Shape, size, and spacing
 large capacitance
 small capacitance

The field is _______ in the central region between the plates, and is _______ at the edges of the plates
As long as the separation between the plates is _____ compared with the dimensions of plates, the edge effects can be ignored

 C = Q/ΔV
 C = (4 nC)/(2.0 V)
 C = 2 nF
 C. 2 nF

What must take place in order to charge a capacitor? The simplest way to do this is to use a source of _______ ________ such as a battery. A battery uses its internal chemistry to maintain a fixed _______ ________ between its ________
 To charge a capacitor, we must move charge from one electrode to the other
 potential difference
 potential difference
 terminals

Charge flows from the top electrode leaving it _______. The charge then flows through the ______ which acts as a _______ ______. The charge ends up on the bottom electrode, making it _______ charged.
The movement of the charge stops when ΔV _{C} is equal to the ______ ______. The capacitor is then ______ ______
If the battery is removed the capacitor _______ ________, with ΔV _{C} equal to the _______ ________
 negative
 battery
 charge pump
 positively
 battery voltage
 fully charged
 remains charged
 battery voltage

Two parallel plates of equal area (A) separated by a distance (d) (assume vacuum in between the 2 plates)
d << dimensions of the plates, so ______ effects can be ignored. Magnitude of the charge per unit area on either plate is:
σ = ____
Electric field is ______ between the plates and _____ elsewhere.
E = _____ = _____ and ΔV = _____ = _____
C = ____ = _____
 edges
 σ = Q/A
 uniform
 zero
**σ is just lower case sigma (Σ upper case)

 Something (probably a battery) was used to generate charge separation (Q) between the electrodes. Then it was a removed, and we know when it (the battery) is removed the capacitor remains charged, so Q is constant
 ΔV = Ed = Qd/ε_{0}A
 E. Both remain constant

 ΔV = Ed if d↑, then E↓ (so B, C and E eliminated)
 C = ε_{0}A/d if C↓ (because d↑) then Q↓ since ΔV is constant (A is eliminated)
 So D.

 A = 1 m^{2}
 d = 1*10^{3} m
 a) C = Q/ΔV = ε_{0}A/d
 C = (8.85*10^{13 }F)(1)/(1*10^{3 }m)
 C = 8.85*10^{9} F
 b) Q = CΔV & ΔV = 100 V
 Q = (8.85*10^{9} F)(100 V) = 8.85*10^{7} C

Define dielectric and give 3 examples
If the dielectric completely fills the space between the plates, the capacitance ________ by the dimensionless factor κ, called the ______ ______ of the material:
C_{with dielectric} = ________
 A Dielectric: an insulating material that increases capacitance when placed between the plates of a capacitor
 Waxed paper, rubber, plastic
 increases
 dielectric constant
 C_{with dielectric} = κC_{without delectric}

Polar molecules are _______ oriented in the absence of an external electric field. When an external electric field is applied, the molecules partially _______ with the field. The charged edges of the dielectric can be modeled as an additional pair of _______ ______ establishing an ______ _____ (___) in the direction opposite that of _____

Label the diagram
Field (arrow right above) due to _______ ______ on dielectric.
(Blue arrow): The net field is the vector sum of the _______ field and the field due to the _______
 induced charges
 applied field
 dielectric

State 3story for Case 1
Then state what happens to:
C
Q
V
E
U_{E }(check this answer with prof.)
 U_{E} decreases by a factor of κ such that (U_{E with dielectric})= (1/κ)(U_{E without dielectric})

State 3story for Case 2
Then state what happens to:
C
Q
V
E

For a parallelplate capacitor with dielectric:
C = ______
In theory, d could be made very small to create a very ______ capacitance.
In practice, there is a limit to d (explain). For a given d, the maximum voltage that can be applied to a capacitor without causing a discharge depends on the _______ ______ of the material

 large
 d is limited by the electric discharge that could occur through the dielectric medium separating the plates
 dielectric strength

A dielectric provides the following advantages (3):

 a) The battery is removed so Q stays the same
 Q = CV = (200 pF)(100 V) = 20000 pC (constant)
 b) decreases by factor of κ = 2.0

The work done in charging the capacitor appears as ______ ______ ______ (___). Or a charged capacitor stores energy as ______ ______ _____:
U_{E} = _____ = _____ = _____ = _____
This applies to a capacitor of any _______
The energy stored increase as the charge ______ and as the potential difference ______. In practice, there is a ______ voltage before discharge occurs between the plates
 electric potential energy (U)
 electric potential energy

 geometry
 increases
 increases
 maximum

A capacitor can charge very slowly and then can release the energy very _______. A medical application of this ability to rapidly deliver energy is the ________.
Define Fibrillation
 quickly
 defibrillation
 Fibrillation: the state in which the heart muscles twitch and cannot pump blood.
 **A defibrillator is a large capacitor that can store up to 360 J of energy and release it in 2 milliseconds. The large shock can sometimes stop fibrillation

The energy stored in a capacitor can be modeled as being stored in the electric field between the plates of the capacitor:
U_{E} = ______ = ______
The energy per unit volume, called the energy density, is:
u_{E} = ________ = ______
The energy density in any electric field is _______ to the square of the magnitude of the electric field at a given point. The energy density has units ______


 proportional
 J/m^{3}
 **Note: (Ad) is basically the volume
 **Note: u_{e} = U_{e}/volume =energy density and is proportional to E^{2}
 This expression is for any kind of capacitor (shape doesn't matter)

 U_{e} = 1/2CV^{2}
 2 mJ = 1/2C(1.5)^{2}
 C = (4*10^{3})/(1.5)^{2} = 1.78*10^{3} F
 Energy stored in the capacitor charged to 3.0 V:
 U_{e} = 1/2(1.78*10^{3} F)(3 V)^{2}
 E. U_{e} = 8 mJ

 U_{e} = 1/2CV^{2}
 C = 2U_{e}/V^{2} = 2(8.4*10^{6})/(23500)^{2}
 C = 3.04*10^{2}F


