Potential gain and potential drop in …

Voltage drops

Whenever current passes through a resistance of some kind, a voltage drop occurs across that resistance. The amount of the drop is given by Ohm's Law: 

V=IR 

Where: 

V = The value of the voltage drop 

I ₌ The current through the circuit in amperes

R = The total resistance of the circuit 

Let's say you have a simple series circuit containing a 10-volt battery, a 3-ohm resistor, and a 2-ohm resistor in series with each other (if the resisitors are in parallel the voltage drop across the "system" of resistors is equivalent to the input voltage of the system, in this example 10 volts. The current flow through each resistor can then be calculated using Ohm's Law). Ohm's Law tells us that 2 Amps are flowing in the circuit (I = V/R = 10/5 = 2). The voltage drop across the 3-ohm resistor is 6 volts (V = IR = 2*3 = 6).