Current Electricity Cheat Sheet by Taneesha

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

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

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

1^st Law :-
At any junction of several circuit elements, the sum of currents entering the junction must be equal to sum of currents leaving it.

2^nd Law:-
The algebraic sum of changes in potential around any closed resistor loop must be zero.

R(s)/R(p) = n²