# Shared Flashcard Set

## Details

Ch 19. DC Circuits
concepts and formulas
41
Physics
02/20/2013

Term
 in order to have an electrical potential difference (aka voltage) that drives  current in an electric circuit, we need a battery or an electric generator ,in this case the battery is a source of ______
Definition
 electromotive force( emf)   (note this is not really a force measured in Newtons, just a bad name).
Term
 describe the electromotive force( emf) of a batery or a electric generator   (aka a source that can generate electrical energy)
Definition
 the potential difference btwn the terminals of the source, where no current flows to an external circuit.   unit: volts
Term
 true or false :is a battery a source of constant current?   if false make it true
Definition
 false, the current out of a battery varies according to the resistance in the circuit.
Term
 true or false :is a battery a source of constant voltage?   if false make it true
Definition
 sort of; a  battery is a source of constant voltage, but NOT  perfectly constant battery has a small internal resistance, which reduces the actual voltage from the ideal emf.
Term
 terminal voltage def (words)
Definition
 the voltage gained by  the battery with respect to terminals in the battery ( ex A & B) has to equal the sum of all the voltage drops due to the prescense of resistors in the circuit
Term
 when no current is drawn from the battery terminal voltage equals?
Definition
 the emf (which is determined by the chemical rxns in the  battery)
Term
 when a current, I,  flows naturally from the battery the terminal voltage equals?
Definition
 there is an internal drop in voltage equal to Ir I= current r= internal resistance (aka this is theACTUAL terminal voltage)
Term
 when 2 or more resistors are connected end to end along a single path from the battery , they are said to be connected in _____.
Definition
 series
Term
 when 2 or more resistors are connected end to end in a series   1.the total voltage is equal to? 2.the total (equivalent)resistance is equal to ?
Definition
 1. sum of the voltages across each resistor (V total= V1+V2+V3) =   recall ohm's law V=IR =  IR1+IR2+IR3 2.Req= R1 +R2+ R3
Term
 for Resistors in Series: The current through each resistor is ______  (equal, less, more), while the voltage depends on the _______. The sum of the voltage 'drops'across the resistors as you go across the all the resistors in the circuit euqals the _____.
Definition
 1.the same 2. resistance 3. battery voltage
Term
 for Resistors in Series: what occurs when you add more resistance to thre circuit?
Definition
 the current through the circuit will decrease.
Term
 1.what is the current of a 12 V battery if it is connected to a 4Ω resitor?  2.also calc for 3 -4Ω resitors in a series?
Definition
 1. V= IR I= V/R I=12/4Ω I= 3A   2. Find total R: 3 x 4Ω = 12Ω I= 12/12Ω I = 1 A
Term
 for a series of resistors that have parallel connection what happens the current? what happens to the voltage across each resistor
Definition
 1.the current is split into seperate paths  2.the voltage across each resistor is the same
Term
 explain the difference btwn resistors that are connected  parallel  vs series
Definition
 Parallel: how a house, buliding is wired , if you disconnect one device the other devices are not interupted.   Series: if one device is disconnected, current is stopped to the others.
Term
 For a parallel arrangemnet of resisitors, why is the voltage across each resistor is the same?
Definition
 the full voltage of the battery is applied to each resistor.
Term
 example: what is the equivalent resistance of 2 -4Ω 'resistors' connected in parallel?
Definition
 1/Req = 1/4Ω + 1/4Ω = 2/ 4Ω = 1/2Ω   so Req= 2 (u flipped 1/2 to 2/1)
Term
 why is the net resistance less for resistors connected parallel?
Definition
 for resistors connected in a parallel circuit the net resistance is less  than the resitance than a SINGLE resistor  b/c the parallel arrangemnt allows the current additional paths to follow.
Term
 when are Kirchhoff’s Rules applied?
Definition
 whenSome circuits cannot be broken down into series & parallel connections
Term
 Kirchhoff’s Rules: what is the junction rule?
Definition
 The sum of currents entering a junction =  the sum of the currents leaving it.
Term
 Kirchhoff’s Rules: what is the loop rule?
Definition
 The sum of the changes in potential around a closed loop ( aka a closed circuit) is zero
Term
 when 2 or more sources of emf such as batteries are arranged in a series, how is the total voltage calculated?
Definition
 the total voltage is the alegebraic sum of the voltages.
Term
 EMFS in parallel only are useful only if
Definition
 only if the voltages of the emfs are the same.
Term
 T or F: EMFs in a parallel arrangement is used to increase voltage   whether true or false , explain
Definition
 False, a parallel arrangement are used to SAVE energy when large currents are needed. ↓ (how they save energy)each of the cells in parallel produce only a fraction of the current. ↓ so the energy loss due to internal resistance would less LESS compared to a single EMF.   (battery will go dead less quickly)
Term
 Circuits Containing Capacitors in Parallel have ______ (same, greater, less)voltage across each one of the capacitors.
Definition
 same
Term
 For Circuits Containing Capacitors in Parallel what is the formula for the total capacitance? (ex you have 3 capacitors)
Definition
 Q= C eq V= C1 V+ C2 V+C3 V (recall voltages are equal for all the capacitors)  or C eq = C1 + C2 +C3      * recall Q= CV Q=charge C=capacitance V= voltage  so its saying the total capitance it just the sum of the capitances (not plugging into the formula which is V=Q/C).
Term
 Why is it useful to connect capacitors in parallel? & why?
Definition
 is to increase the capitance  b/c we are increasing the area of the plates where charge can accumulate
Term
 Circuits Containing Capacitors in Series have ________(same,greater,less) charge.
Definition
 same
Term
 Give the formula the total (equivalent) capitance of a circuit with 3 capacitors.
Definition
 recall Q=CV V=Q/C1+ Q/C2+ Q/C3 = Q( 1/C1 + 1/C2+ 1/C3)   1/Ceq= 1/C1 + 1/C2 + 1/C3   just flip it b/c this is the reciporcal (e.g 1/2 = 2/1=2)
Term
 do rc circuits flash cards next
Definition
 do rc circuit  flash card  next
Term
 An ammeter measures
Definition
 current  (remember unit is amps)
Term
 a voltmeter measures
Definition
 voltage
Term
 Ammeters and Voltmeters are based on _________, unless they are digital
Definition
 galvanometers
Term
 b/c the current in a circuit passes through the ammeter; the ammeter should have  _____(high/low) resistance so as not to affect the current.
Definition
 low
Term
 A voltmeter should not affect the voltage across the circuit element it is measuring; therefore its resistance should be very (small/large)
Definition
 large
Term
 An ohmmeter measures resistance; it requires ______
Definition
 1.resistance 2.a battery to provide a current   *If the meter has too much or (in this case) too little resistance, it can affect the measurement.
Term
 Convential current is flow of current from the _____ terminal to the ___ terminal
Definition
 positive to negative
Term
 the resistance of a conductor is a measure of it's
Definition
 resistance to current flow.
Term
 what is a resistor?
Definition
 a device that is used  intenially to cause a  voltage drop in the circuit
Term
 formula for resistance R
Definition
 R= ρL/ A
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