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Flashcards in Electronic Circuit Elements Deck (20):


I = ΔQ/Δt. 

Current is the rate of charge flow through the cross-section of a conductor (wire).


Battery, electromotive force, voltage

Electromotive force (emf) is really not a force, but a potential difference, with the unit voltage. 

A battery is a source of emf. 

If the battery has no internal resistance, then potential difference across the battery = EMF. 

If the battery has internal resistance, then potential difference across battery = EMF - voltage drop due to internal resistance.


Terminal potential

Voltage across terminals of battery; EMF - IRinternal


Internal Resistance

Internal resistance of a battery is like a resistor right next to the battery connected in series.


Ohm's Law

V = IR


Resistors In Series

Iseries = I1 = I2 = I3

All resistors in series share the same current. 

Vseries = V1 + V2 + V3


Resistors in Parallel

Vparallel = V1 = V2 = V3. 

All resistors in parallel share the same voltage. 

Iparallel = I1 + I2 + I3



ρ = RA/L

For higher resistivity, keep wire with high resistance and high area and low length. 


Concept of parallel-plate capacitor

C = Q/V = εA/d

Greater capacitance is created by a greater charge on plates (Q) for a given voltage (V), greater plate area (A), or smaller distance between plates (d). 

V = Ed, where V is voltage across capacitor, E is electric field between capacitor, and d is the distance between capacitor plates


Energy of a Charged Capacitor

U = Q2/2C = ½QΔV = ½C(ΔV)2 

U is the potential energy of the charged capacitor, Q is charge stored (magnitude of either +Q or -Q on one of the plates), C is capacitance.


Capacitors in Series

1/Ceq = 1/C1 + 1/C2 + 1/C3


Capacitors in Parallel

Ceq = C1 + C2 + C3



Dielectric = nonconducting material. 

Inserting a dielectric between the plates of a capacitor increases the capacitance by either increasing Q (if V is constant) or decreasing V (if Q is constant). 

V = V0

C = κC0


Discharge of a capacitor through a resistor

During the discharge of a capacitor, the capacitor acts as a battery and drives current flow, which decreases with time as the capacitor discharges.


Conductivity theory: concentration of electrolytes

Conductivity is affected by electrolyte concentration: 

No electrolyte, no ionization, no conductivity. 

Optimal concentration of electrolyte, greatest conductivity due to greatest mobility of ions. 

Too much electrolyte, ions are too crowded, less ion mobility, less conductivity.




Conductivity Theory: Temperature

Conductivity is affected by temperature: 

In metals, conductivity decreases as temperature increases.

In semiconductors, conductivity increases as temperature increases. 

At extremely low temperatures (below a certain critical temperature typically a few degrees above absolute zero), some materials have superconductivity - virtually no resistance to current flow, a current will loop almost forever under such conditions.




Power in Circuits

P = IV = I2R



To minimize P dissipated by the wires....

minimize I by maximizing V. This is why power lines transfer electricity at high voltage.


Root-mean-square current of AC

Irms = Imax/√2 = 0.7 Imax


Root-mean-square voltage of AC

Vrms = Vmax/√2 = 0.7 Vmax