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Physics and Math > Circuits > Flashcards

Circuits Flashcards

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1
Q

metallic conductivity

A

in solid metals and the molten forms of some salt; free flow of electric charge due to metal atoms losing their outer electrons

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2
Q

electrolyte conductivity

A

seen in solutions; depends on the strength of a solution and can be used to determine the ionic concentrations in solutions

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3
Q

conductance

A

the reciprocal of resistance, a measure of permissiveness to current flow; units are siemens (S)

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4
Q

current (I)

A

the flow of charge between two points at different electrical potentials connected by a conductor; unit is ampere (1 A= 1 C/s)

I= Q/ delta t

Q= charge
t=time

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5
Q

how is charge transmitted?

A

through the flow of electrons in a conductor, moving from a point of lower electrical potential to a point of higher electrical potential

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6
Q

what is the direction of current?

A

in the direction in which positive charge would flow; from higher potential to lower potential. Current flows in the opposite direction of actual electron flow (charge)

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7
Q

direct current (DC)

A

the charge flows in one direction only

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8
Q

alternating current (AC)

A

the charge flow changes direction periodically

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9
Q

electromotive force (emf or e)

A

measured voltage when no charge is moving between the two terminals of a circuit that are at different potential values; it is not a force, it is the potential difference (voltage); units are J/C=V

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10
Q

what is an electric circuit?

A

a conducting path that usually has one or more voltage sources (battery) connected to one or more passive circuit elements (such as resistors)

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11
Q

Kirchhoff’s Junction Rule

A

at any point or junction in a circuit, the sum of currents directed into that point equals the sum of currents directed away from that point
I into junction= I leaving junction

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12
Q

Kirchhoff’s Loop Rule

A

around any closed circuit loop, the sum of voltage sources will always be equal to the sum of voltage (potential) drops
Vsource=Vdrop

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13
Q

resistance

A

the opposition within any material to the movement and flow of charge; motion is being opposed

R= pL/A

R=resistance
p=resistivity
L=length of the resistor
A=cross sectional area

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14
Q

conductors

A

give almost no resistance

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15
Q

insulators

A

give very high resistance

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16
Q

resistivity

A

number that characterizes the intrinsic resistance to current flow in a material; unit is Ohm-meter (omega x m)

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17
Q

length of the resistor

A

directly proportional to the resistance of a resistor; if a resistor doubles its length, the resistance will also be doubled

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18
Q

conduction pathways

A

the number of pathways that are available for charge to move through; this is the idea behind cross sectional areas affect on resistance, if you double the area, the resistance is cut in half

19
Q

temperatures affect on resistance

A

most conductors have greater resistance at higher temperatures due to increased thermal oscillation of the atoms in the conductive material which produces a greater resistance to electron flow

20
Q

Ohm’s law

A

states that for a given resistance, the magnitude of the current through a resistor is proportional to the voltage drop across the resistor

V=IR

V=voltage drop
I=current
R=magnitude of the resistance (ohms)

21
Q

the voltage supplied by a cell to a circuit

A

V=Ecell - ir(int)

V=voltage provided the cell
Ecell= emf of the cell
i= current through the cell
r(int)= internal resistance

if no internal resistance is present, then the voltage is equal to the emf

22
Q

galvanic (voltaic) cell vs electrolytic cell

A

a galvanic cell discharges, meaning that it supplies a current; while an electrolytic cell (secondary battery) recharges, meaning an external voltage is applied in such a way to drive current toward the positive end of the battery

23
Q

power of a resistor

A

rate at which energy is dissipated by a resistor

P=IV=(I^2)R= (V^2)/R

I=current through the resistor
V=voltage drop across the resistor
R=resistance of the resistor

24
Q

resistors in series

A

current has to travel through each resistor in order to return to the cell; energy is dissipated as electrons flow through each resistor, so there is a voltage drop through each resistor

25
Q

resultant resistance in series

A

total resistance is just the sum of all the resistors

Rs= R1+R2+R3….

26
Q

resistors in parallel

A

in this case, resistors are connected in parallel with a common high potential terminal and a common low potential terminal; the voltage drop is the same because all pathways originate from a common point and end at a common point within the circuit

27
Q

for resistors in parallel, is the voltage and resistance the same for each pathway?

A

the voltage is the same for all parallel pathways, but the resistance of each pathway may differ; so electrons will prefer the path of least resistance, so current will be largest through the pathways with the lowest resistance

28
Q

resultant resistance in parallel

A

there is a net reduction in resistance; could replace all resistors in parallel with a single resistor that has a resistance that is less than the resistance of the smallest resistor in the circuit
1/Rp=1/R1 + 1/R2 + 1/R3….
Rp will always decrease as more resistors are added

29
Q

capacitors

A

have the ability to store and discharge electrical potential energy; they store an amount of energy in the form of charge separation at a particular voltage

30
Q

capacitance

A

defined as the ratio of the magnitude of the charge stored on one plate to the potential difference (voltage) across the capacitor; unit is farad (1 F= 1 C/V)

C=Q/V

31
Q

capacitance of parallel plate capacitor

A

C= eo (A/d)

eo= is the permittivity of free space (8.85x 10^-12 F/m)
A=area of overlap of the two plates
d= separation of the two plates

32
Q

uniform electric field

A

created by the separation of charges

E= V/d

d=separation of the two plates
direction of the electric field is from the positive to the negative plate

33
Q

potential energy in a capacitor

A

U= (1/2)CV^2

34
Q

dielectric constant (k)

A

the value of the increase in capacitance when you stick a dielectric material (insulator) in between the plates of a capacitor; measure of the insulating ability of that material

35
Q

capacitance due to a dielectric material

A

C’ = kC

C’= the new capacitance with the dielectric material present

36
Q

what happens when a dielectric material is placed in a isolated, charged capacitor?

A

the voltage across the charged capacitor will decrease, thus increasing the capacitance

37
Q

what happens when a dielectric material is placed in a charged capacitor within a circuit?

A

the charge on the capacitor increases because the voltage must remain constant in circuits. thus it still increases the capacitance

38
Q

capacitors in series

A

the total capacitance decreases in similar fashion to the decrease in resistance in parallel resistors; this due to capacitors having to share the voltage drop n the loop so they cannot store as much charge

1/Cs= 1/C1 + 1/C2 + 1/C3….
Cs decreases as more capacitors are added, the voltage is the sum of the individual voltages

39
Q

capacitors in parallel

A

produce a resultant capacitance that is equal to the sum of the individual capacitances

Cp= C1+C2+C3…
the voltage across each parallel capacitor is the same and is equal to the voltage across the source

40
Q

meters

A

devices that are used to measure circuit quantities in the real world

41
Q

ammeters

A

are inserted in series in a circuit to, used to measure the current at some point within a circuit; ideal ones have zero resistance and no voltage drop

42
Q

voltmeter

A

are inserted in parallel in a circuit to measure a voltage drop (potential difference); have very large resistances

43
Q

ohmmeters

A

are inserted at two points in series with a circuit element of interest, used to measure resistance; they are self powered and have negligible resistance, ideal resistance of zero

Physics and Math (12 decks)

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