Question

If the electrical potential difference is the difference in electrical potential then how it it is a measure done with the help of test charge , then how it causes electron to flow ?

Answer 1

What is potential difference? It's pretty simple, actually.

• A charge repels other like charges (with same sign). That means, an electron repels other electrons.
• If you at one point have, say, 10 electrons then they will try to move as far away from each other as they can.
• This point with many electrons (that is, this point that electrons are strongly repelled from) is said to have high potential. A point of less repulsion is said to have lower potential.

In this way, electrons will always try to move towards the lower potential. In other words: if there is a potential difference between two points then electrons will try to move because they experience an electric force towards the lower potential.

How can such a potential difference be established? That's also pretty simple, actually.

To create and sustain a potential difference you need something to move charges "the wrong way". That is, towards the point of higher potential. You just need a force larger than the repelling force.

• a battery is a clear example. Inside the battery a chemical process creates such a force which pushes the electrons back up to the higher potential point (the negative pole/terminal of the battery).
• From this point they again want to move back to the lower potential. They do this by running through the circuit ("around" the battery).
• When the electrons reach the lower potential, which is the positive pole/terminal of the battery, they are moved back up again on the higher potential ready to travel once more.