Chapter 6: Circuits Flashcards
conductance unit
siemens (S)
conductivity unit
S /m
current
I = Q / Δt
unit is ampere (1 A = 1 C /s)
what are the two types of conductivity?
metallic conductivity and electrolytic conductivity
electromotive force (emf)
when no charge is moving between the two terminals of a cell that are at different potential values
unit is volts
Kirchhoff’s junction rule
I into junction = I leaving junction
At any point junction in the circuit, the sum of currents directed into that point equals the sum of currents directed away from that point.
Kirchhoff’s Loop Rule
V source = V drop
The sum of voltage sources will always be equal to the sum of voltage drops. All the electrical energy supplied by a source gets fully used up by the other elements within the loop.
resistors equation
R = ρL / A
ρ = resistivity
L = lenght of the resistor
A = cross sectional area
what affects a resistor?
lenght, resistivity, temperature and cross sectional are
resistivity (ρ)
unit is ohm -meter = Ω .m
Ohm’s Law
V = IR
V = voltage drops
I = current
R = magnitude of the resistance , measured in ohms
actual voltage supplied by a cell is
V = Ecell - irint
V = volatge provided by a cell
Ecell = emf of that cell
i = current throught that cell
rint = internal resistance
power
P = W / t = ΔE / t
P = IV = I^2R = V^2/ R
resistors in series
All current must pass sequentially through each resistor connected in a linear arrangement.
Vs = V1 + V2 + V3 + …+ Vn
Rs = R1 + R2 + R3 + …+ Rn
what to do when approachign circuit problems?
The first thing you need to find are the total circuit values: The total voltage, the total resistance and the total current. To find it to recurrent, first find the total resistance of the circuit.
resistor in parallel
The current will divide to pass through resistor separately. If every resistor is parallel, then the voltage drop across each pathway alone must be equal to the voltage of the source. Electrons before the path of least resistance. The current will be the largest through the pathways with the lower resistance.
Vp = V1 = V2 = V3 = …= Vn
1 /Rp = 1/R1 + 1/R2 + 1/ R3 + … + 1/Rn
capacitance equation
C = Q / V
Q = charge it collects
C = capacitance
V = potential difference (voltage)
units for a capacitance
farad (1 F = 1 C /V)
usually given in microfarads (1μF = 1 x 10^-6 F)
potentail energy stored in a capacitator
U = 1/2 C V^2
uniform electric field
E = V / d
the direction of electriv field at any point between the plates is from the positive plae towards the negative plate
dieletric material
it increases the capacitance by a factor called the dielectric constant (k)
capacitance due to a dieelectric material
C’ = k C
C’ = new capacitance
C = original capacitance
capacitors in series
1/ Cs = 1/C1 + 1/C2 + 1/C3 + ….+ 1/Cn
Cs decreases as more capacitors are added. The total voltage is the sum of the individual voltages.
capacitors in parallel
Cp = C1 + C2 + C3 + … + Cn
how does dieletric material impact capacitance? voltage? charge?
capacitance: always increase capacitance
voltage: if is isolated, voltage will decrese, if in a circuit voltage is constant
charge: if isolated, it will remain constant.If in a circuit it will increase
how does adding or removing a capacitor change the total capacitance of a circuit with capacitors in series? in parallel?
series: adding it will decrease total capacitance
parallel: adding will increase capacitance
isolated capacitors
disconnected from any circuit
ammeters
used ot measure the current at some point within a circuit
voltmeter
used to measure the volatge drop across two points in a circuit.
ohnmeter
calculate resistance by knowing the ohnmeter voltage and the current created thought another point in the circuit.
