# Circuits I

 .remove_background_ad { border: 1px solid #555555; padding: .75em; margin: .75em; background-color: #e7e7e7; } .rmbg_image { max-height: 80px; } 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)zerocharge In a capacitor, the electric field strength E and the potential difference ΔVC _______ as the charge on each electrode ________. Define the capacitance, C and state the identity increases increasesCapacitance, 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 conductorsmallelectrode 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 positivefarad (F)microfarads (μF) and picofarads (pF)geometric Shape, size, and spacinglarge capacitancesmall 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 uniformnonuniform small C = Q/ΔV C = (4 nC)/(2.0 V)C = 2 nFC. 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 otherpotential difference potential differenceterminals 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 ΔVC is equal to the ______ ______. The capacitor is then ______ ______ If the battery is removed the capacitor _______ ________, with ΔVC equal to the _______ ________ negativebatterycharge pumppositively battery voltagefully chargedremains chargedbattery 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/Auniform 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/ε0AE. Both remain constant ΔV = Ed if d↑, then E↓ (so B, C and E eliminated) C = ε0A/d if C↓ (because d↑) then Q↓ since ΔV is constant (A is eliminated)So D. A = 1 m2 d = 1*10-3 ma) C = Q/ΔV = ε0A/d C = (8.85*10-13 F)(1)/(1*10-3 m)C = 8.85*10-9 Fb) Q = CΔV & ΔV = 100 VQ = (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: Cwith dielectric = ________ A Dielectric: an insulating material that increases capacitance when placed between the plates of a capacitorWaxed paper, rubber, plasticincreasesdielectric constantCwith dielectric = κCwithout 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 3-story for Case 1 Then state what happens to: C Q V E UE (check this answer with prof.) UE decreases by a factor of κ such that (UE with dielectric)= (1/κ)(UE without dielectric) State 3-story for Case 2 Then state what happens to: C Q V E For a parallel-plate 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 sameQ = 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 ______ ______ _____:  UE = _____ = _____ = _____ = _____ 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 geometryincreasesincreases 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 quicklydefibrillation 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: UE = ______ = ______ The energy per unit volume, called the energy density, is: uE = ________ = ______ 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/m3 **Note: (Ad) is basically the volume**Note: ue = Ue/volume =energy density and is proportional to E2This expression is for any kind of capacitor (shape doesn't matter) Ue = 1/2CV22 mJ = 1/2C(1.5)2C = (4*10-3)/(1.5)2 = 1.78*10-3 FEnergy stored in the capacitor charged to 3.0 V: Ue = 1/2(1.78*10-3 F)(3 V)2 E. Ue = 8 mJ Ue = 1/2CV2C = 2Ue/V2 = 2(8.4*106)/(23500)2C = 3.04*10-2F .remove_background_ad { border: 1px solid #555555; padding: .75em; margin: .75em; background-color: #e7e7e7; } .rmbg_image { max-height: 80px; } Authorchikeokjr ID346749 Card SetCircuits I DescriptionCircuits I Updated2019-05-13T04:31:40Z Show Answers