Circuits

Question 1

metallic conductivity

Answer 1

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

Question 2

electrolyte conductivity

Answer 2

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

Question 3

conductance

Answer 3

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

Question 4

current (I)

Answer 4

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

Question 5

how is charge transmitted?

Answer 5

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

Question 6

what is the direction of current?

Answer 6

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)

Question 7

direct current (DC)

Answer 7

the charge flows in one direction only

Question 8

alternating current (AC)

Answer 8

the charge flow changes direction periodically

Question 9

electromotive force (emf or e)

Answer 9

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

Question 10

what is an electric circuit?

Answer 10

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

Question 11

Kirchhoff’s Junction Rule

Answer 11

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

Question 12

Kirchhoff’s Loop Rule

Answer 12

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

Question 13

resistance

Answer 13

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

Question 14

conductors

Answer 14

give almost no resistance

Question 15

insulators

Answer 15

give very high resistance

Question 16

resistivity

Answer 16

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

Question 17

length of the resistor

Answer 17

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

Question 18

conduction pathways

Answer 18

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

Question 19

temperatures affect on resistance

Answer 19

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

Question 20

Ohm’s law

Answer 20

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)

Question 21

the voltage supplied by a cell to a circuit

Answer 21

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

Question 22

galvanic (voltaic) cell vs electrolytic cell

Answer 22

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

Question 23

power of a resistor

Answer 23

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

Question 24

resistors in series

Answer 24

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

Question 25

resultant resistance in series

Answer 25

total resistance is just the sum of all the resistors | Rs= R1+R2+R3....

Question 26

resistors in parallel

Answer 26

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

Question 27

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

Answer 27

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

Question 28

resultant resistance in parallel

Answer 28

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

Question 29

capacitors

Answer 29

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

Question 30

capacitance

Answer 30

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

Question 31

capacitance of parallel plate capacitor

Answer 31

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

Question 32

uniform electric field

Answer 32

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

Question 33

potential energy in a capacitor

Answer 33

U= (1/2)CV^2

Question 34

dielectric constant (k)

Answer 34

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

Question 35

capacitance due to a dielectric material

Answer 35

C' = kC C'= the new capacitance with the dielectric material present

Question 36

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

Answer 36

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

Question 37

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

Answer 37

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

Question 38

capacitors in series

Answer 38

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

Question 39

capacitors in parallel

Answer 39

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

Question 40

meters

Answer 40

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

Question 41

ammeters

Answer 41

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

Question 42

voltmeter

Answer 42

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

Question 43

ohmmeters

Answer 43

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