[1] Open circuits have an opened switch, without current flow (0 A).
Closed circuits have a closed switch, which can turn on loads like light bulbs.
Short-circuits are closed circuits of 2 equipment pieces at different voltages connected with small resistance between, causing overcurrent and cause fires.
Short circuits have 3 main types: series, parallel, and line-to-ground short circuits.
Short circuits have max current and no voltage.
It implies 2 terminals connect externally with 0 resistance.
[2] Kirchhoff's voltage law (KVL)/The conservation of energy says all voltages' sum in a circuit's closed loop equals zero, as a circuit loop is a closed conducting path so no energy is lost--moving around a closed loop/circuit gets back to start point, so back to the same initial potential without voltage loss.
[2] Assume the current (I) is in the same direction as positive flow charge (conventional current flow).
This current flow in the resistor is from A to B (positive to negative terminal) is a fall in potential across the resistor making a voltage drop across.
A rise is if the current goes the opposite way, B to A (negative to positive terminal) across the resistor, making a +I*R voltage drop.
To use KVL correctly, first know polarity direction as the voltage sign drop on resistors depend on current flow direction. Generally we loose potential in the same way of current across an element and get potential as we move in the way of an electromotive force source.
electromotive: source's difference if no current flows; not confused by "voltage" = potential difference if current flows
Current direction flow is either clockwise/anticlockwise. If the direction used is different from the true direction, the result is still correct and valid but with the a minus sign in the algebraic answer.
[1] KLV says potential differences' sum in any loop equals zero: ΣV = 0. Since the resistors, R1 and R2 are series, both are of the same loop so the same current flow through each resistor.
So voltage drop of R1 = I*R1 and R2 = I*R2 by KVL:
Using KVL to this single closed loop makes the formula for the equivalent/RT in the series circuit and we can expand this to find the voltage drops values around the loop.
E.g. 1# 3 resistor of 10Ω, 20Ω and 30Ω, respectively connect in series across a 12 V DC battery.
Find RT, IT, current and voltage per load, and verify KVL.
RT = 10Ω + 20Ω + 30Ω = 60Ω
IT = 12V/60Ω = 0.2 A
R10Ω = 0.2x10 = 2 V
R20Ω = 0.2x20 = 4 V
R30Ω = 0.2x30 = 6 V
Verify KVL:
