Voltage Drop - When does it Matter?

Let's start by defining what voltage drop is.

According to Wikikpedia: Voltage drop is the decrease of electrical potential along the path of a current flowing in an electrical circuit. 

What does this mean?  Well, take a look at the diagram below.

** diagram 01**

If we take a voltage measure ment across the lamp we will find the volt meter indicate 12 Volts.  So he voltage drop of this circuit is equal to the supply voltage of 12 Volts.

But what is the voltage drop in the circuit below?

** diagram 02 **

If we connect a volt meter between the positive battery terminal and the junction of the two lamps we will find the voltage drop is 6 Volts.  We know the potential at the battery is 12 Volts, so can deduce that the voltage drop over the second lamp is also 6 Volts.

Each element of the circuit is introducing some resistance, so each element of the circuit contributes to the voltage drop.

But there are elements we have not cosidered in the previous examples - the wires, the cables.  Even the highest quality copper cables introduce some resistance and therefore voltage drop.  Lets go back to the first drawing.

** diagram 01 **

Lets make some assumptions:

The lamp is 5 metres from the battery

The cable is quite light, at 1.0 sq mm.

The lamp is a 60 watt lamp.