DIRECT CURRENT

A direct current (dc) flows in one direction , either steadily or in pulses.:

Current (I)    - The quantity of electrons passing a given point (unit : ampere)

Voltage (V) - Electrical pressure or force (unit : volt)

Resistance(R) - Resistance to the flow of a current, (unit : ohm)

Power (P) - the work performed by a current , (unit : watt)

Potential Difference - the difference in voltage between the two ends of a conductor through which a current flows , also known as a voltage drop.

OHM'S LAW

Ohm's Law Helper Diagram 

A potential difference of 1 volt will force a current of 1 Ampere through a resistance of 1 ohm, or :

V = I x R

I  = V/R

R = V/I

P = I x V (or) I^2 x R

Resistor Networks

SERIES

Rt = Total Resistance

Rt = R1 + R2 + R3

PARALLEL

Rt = Total Resistance 

Rt = [R1 x R2]/[R1 + R2]

PARALLEL (2 or more)

Rtotal (Rt) = 1/ [1/R1 + 1/R2 + 1/Rn]

VOLTAGE DIVIDER 

Vout = Vin x [ R1/(R1 + R2)]

R1 and R2 can be a potentiometer