Question

why potential is different in series

Answer 1

 You must be aware that resistances in series are added together to find the resultant resistance. Say, we have three components connected in series with values 1, 2 and 3 ohms respectively. So the total resistance of the combination would be 1+2+3=6 ohm. Let us also assume thet the power supply is a 6V battery. So when the battey is cinnected across this series circuit, Ohm's law (I=V/R) tells us that current through this circuit is 6/6=1A.

As for the voltage or potential difference across each circuit component is again given by Ohm's law's another form, V=IR. So voltage across the 1 ohm resistance would be 1*1=1V, across the 2 ohm resistance, 1*2=2V and across the 3 ohm resistance, 1*3=3V.

Isn't that pretty simple