Circuits Flashcards
current
flow of positive charge
will be moving in the opposite direction of the electrons
represented by “I”
current equation
I = Q/t
unit = Amps
A = C/s
Amps
unit for current
A = C/s
metallic conductivity
creates electrical change because metals are highly conductive –> easily able to release outer electron
electrolytic conductivity
depends on strength of solution
low ion concentration acts more like an insulator
which way do electrons move
from low to high electric potential
reduce electric potential energy as moves closer to higher electric potential
electromotive force
pressure to move that results in current
voltage when no current is flowing
V = J/C
denoted as emf or E
Kirchoff’s Loop Rule
Vsource = Vdrop
all energy must be used up during the loop so that
ΔV=0
don’t want electric charge to build up
Kirchoff’s Junction Rule
I into = I out
electrical charge must be conserved
Resistance
opposition within any material to movement and flow of charge
conductors
offer almost no resistance
Resistors
offer some resistance
insulators
offer high resistance
Resistance equation
resistivity x length/area
ρL/A
as length increases or area decreases, resistance increases
Ohm’s Law
V=IR
Power equation with Ohm’s Law
P = W/t = ΔE/t
P=IV=I^2 R = V^2/R
Resistors in series
energy drop associated with each resistor so voltage drop is additive. V1 + V2 + … Vn
V=IR therefore:
Rs = R1 + R2 + R3 + … Rn
Resistors in parallel
Vp = V1 = V2 = V3
however, electrons prefer the path of least resistance, so current will be largest where there is the lowest resistance
1/Rp = 1/R1 + 1/R2 + … 1/Rn
Rp will decrease as more resistors are added
Capacitor
does not store charge
stores imbalance of charge
if one capacitor has +1 C of charge, the other plate will have -1C; therefore the net charge is 0
Capacitor’s potential energy equation
U = 1/2CV^2
capacitance
amount of charge that can build up - how much of a charge difference there is between 2 oppositely charged plates that are held at a distance away
with plates the higher potential side will be positive and the lower potential side will be negative
C=Q/V
simple parallel plate capacitor equation
C = ε (A/d)
capacitance - permeability of free space (8.85x10^-12F/m) (area of overlap/distance separation of 2 plates)
Capacitance is in Farads
Farad
capacitance unit
F = C/V (coulomb/volt)
dielectric
insulator
plastic, glass, ceramics, or certain metal oxides
what happens with addition of dielectric material?
increase capacitance by a factor called the dielectric constant (k)
Capacitance due to dielectric material
C’ = kC
new capacitance = dielectric constant x old capacitance
Capacitors in series
opposite of resistors
total capacitance will decrease because have to share the voltage drop
1/Cs = 1/C1 + 1/C2 + …
Cs decreases with the addition of capacitors
Capacitors in parallel
opposite of resistors
More capacitors = more charge
Cp = C1 + C2 + …
Ammeters
used to measure current at some point within current
current must be on or at 0A
wired in series
Voltmeters
requires current
use magnetic properties to measure voltage drop across 2 points in a circuit
wired in parallel
What happens to the emf when current is flowing?
since emf is the voltage when current is not flowing, will need to calculate the drop in voltage by multiplying current by internal resistance.
V = Ecell - ir
resistivity
p=RA/L
intrinsic property of the medium and remains the same when the area of the plate is changed
Parallel Circuits
the current will change depending on the resistance because will want to follow the path of least resistance
voltage will remain the same throughout the circuit because V = IR (we already know that if R decreases, I will increase and we will keep V constant)
therefore
Vtotal = V1 = V2 = V3 Itotal = I1+ I2 + I3
Series Circuits
the current will stay the same throughout the whole circuit and voltage will change depending on resistance
the higher the resistance, the more the voltage will drop because V = IR
with I staying constant - larger R means larger V
therefore
Vtotal = V1 + V2 + V3 Itotal = I1 = I2 = I3
