Question

How come the potential difference changes in resistors in series

Answer 1

short circuit:

As we know that current flowing in a short circuit has no opposition ideally. It means no energy is consumed there in opposing current , so no voltage drop occur . because voltage and energy are enter related by v=W/q.

Circuit with a Resister:

Now, if we have a resister then we have opposition in the path of current . this means energy is consumed and so voltage drops occur.

Circuit with Multiple Resister:

Coming to your question , just imagine circuit with two resister. Each of them is opposing current .but it is possible that one may oppose less and other may more. As a result voltage drop across them may or may not be same depending upon resister values.

Conclusion:

Voltage drop occur due to the energy consumption in the path of flowing electrons in circuits. it may be by a single resister or may be by more than one resister.