Cheatography

# Current Electricity Cheat Sheet by Taneesha

current electricity cheat sheet

### Basic notations

 current (I) q/t q charge V terminal voltage resistance (R) V/I or ρ l/A
in the formula for resist­ance, the first formula has current and the second one has length of the resistor

### Effect of stretching of wire on resistance

 L -- original length of wire A -- original cross-­sec­tional area L' -- length of wire after stretching A' -- cross-­sec­tional area of wire after stretching final resist­ance, R' = n2R

### Resistors in Series

 V = IR(s) ......[­R(s) is equivalent resistance for resistors in series] general formula for 'n' resistors in series -- R(s) = R(1) + R(2) + R(3) + ......... + R(n) ∴ R(s) = n R
n --- no. of equal resistors

### Resistors in Parallel

 I = V/R(p) .....[R(p) is equivalent resistance for resistors in parallel] general formula for 'n' resistors in parallel -- 1/R(p) = 1/R(1) + 1/R(2) + 1/R(3) + .... + 1/R(n) ∴ R(p) = R/n

### Kirchoff's Laws

 1st Law :- At any junction of several circuit elements, the sum of currents entering the junction must be equal to sum of currents leaving it. 2nd Law:- The algebraic sum of changes in potential around any closed resistor loop must be zero.

### Relation b/w R(s) & R(p)

 R(s)/R(p) = n2

### Wheatstone Bridge

Here if,
P/R = Q/S or
P/Q = R/S, then,
we can simply remove G.
Now, P & Q are in series and R & S are in series, and the combin­ation of the two are in parallel