Q-Why when resistance is connectedIn series combination P.D.changes but when it is connected in parallel combination amount of current changes.
In a series circuit resistors are connected in a straight line (one after another) without any branch offs...
now, in a series circuit as there are branches the current has no other way to go but through the single lane of resistors each one using some value of the voltage provided by the battery. So, here the voltage varies as it is indirectly connected to each resistor but the current stays constant throughout.
however, in a parallel circuit the resistor are connected in branches with no straight path between them , here branching off occurs...
so, as there are different branches in a parallel circuit the current has to move in separate lines and it splits from its original value. This splitting results in the changing values of current in for each resistor. Now, as each resistance is connected directly to the battery (across its terminals) in this case the voltage remains constant for across each resistor.