Circuits Flashcards
Current
the movement of charge that occurs between two points that have different electrical potentials. By convention defined by a positive charge from the high potential end of a voltage source to the low. In reality it is negatively charged particles (electrons) that move in a circuit, form low potential to high potential.
I = Q/Δt
Current only flows..
in conductive material
Metallic conduction
relies on uniform movement of free electrons in metallic bonds
electrolytic conduction
relies on the ion concentration of a solution
Insulators
are materials that do not conduct a current
Kirchoffs laws
express conservation of charge and energy
kirchhoffs junction rule
states that the sum of currents directed into a point within a circuit equals the sum of currents directed away form that point.
I into junction = I leaving junction
Kirchhoffs loop rule
states that in a closed loop, the sum of voltage sources is always equal to the sum of voltage drops.
Vsource = Vdrop
Resistance
is opposition to the movement of electrons through a material
R = pL/A
resistors
are conductive materials with a moderate among to resistance that slow down electrons without stopping them. calculated using resistivity, length, and cross-sectional are of the material in question.
Ohm’s law
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
Resistors in series
are additive and sum together to create the total resistance of a circuit
resistors in parallel
cause a decrease in equivalent resistance of a circuit
Across each resistor in a circuit…
a great amount of power is dissipated, which is dependent on the current through the resistor and through voltage drop across the resistor.
capacitors
have the ability to store and discharge electrical potential energy
capacitance
in parallel plat capacitors is determined by the area of the plates and the distance between plates
C = Q/V
capacitors in series cause
a decrease in the equivalent capacitance of a circuit
Capacitors in parallel
sum together to create a larger equivalent capacitance
Dielectric materials
are insulators placed between the plates of a capacitor that increase capacitance by a factor equal to the material’s dielectric constant, k.
C’ =kC
Ammeters
are inserted in series in a circuit to measure currents, they have negligible resistance
Voltemeters
are inserted in parallel in a circuit to measure a voltage drop; they have very large resistance.
Ohmmeters
inserted around a resistive element to measure resistance; they are self powered and have negligible π
Voltage and cell emf
V=E cell -ir int
Power
P = W/t = ΔE/t
electric power
P=IV=I^2R=V^2/R
Voltage drop across circuit elements (series)
Vs=V1+V2+V3+Vn
Equivalent resistance in series
Rs=R1+R2+R3
Voltage drop across circuit elements parallel
Vp=V1=V2=V3`
Equivalent resistance parallel
1/Rp=1/R1 + 1/R2 + 1/Rn
Capacitance based on parallel plate geometry eq
C=e0(A/d)
electric field in a capacitor
E = V/d
Potential energy of a capacitor
U = 1/2 CV^2
Equivalent capacitance in series
1/Cs = 1/C1 + 1/Cn
Equivalent capacitance in parallel
Cp = C1 + C2 + Cn
