# Potential Difference of a battery - What does it mean?

I have studied current electricity for a while now. When I look back at basic concepts, I am quite clear about what current, electron, resistance is. But I cannot imagine about the potential difference or voltage of a battery. Or in a circuit, it is said that potential drops across a resistance, why is that so? What does it mean to have a potential difference? I asked my friends too, but none of them have quite understood the concept too. So, can you clarify the concept of p.d? using analogies or any way that might easy.

• From my understanding, the potential difference between point A and point B is the amount of work done by an electric field on a charge should it move from point A to point B. This is analogous to a ball falling towards the earth under the influence of gravity. Dec 26, 2018 at 14:06
• To be honest I don't get why potential drops over a resistor. From what I can see it should be dependent on the displacement of the charge, like how GPE is dependent on height. Maybe someone can clarify XD. Dec 26, 2018 at 14:10
• Maybe for a start, you can consider dropping a ball through a long frictionless tube that has some sandpaper in the middle. The ball represents an electron, the sandpaper is the resister and gravity is the EMF. But this is not a good analogy because unlike current, the ball is not continuous. An alternative analogy might be trying to push a long cylinder through a frictionless tube with pieces of sandpaper in it. In this case, the cylinder represents current. You can see how the friction exerted by different pieces of sandpaper can stack up, which is why you can add up resistance in a circuit. Dec 26, 2018 at 14:30

Basically it all comes down to potential energy. A battery supplies electrical potential energy that can enable electrical current to flow. The source of the battery’s energy is conversion of chemical energy. An analogy is a water pump supplies mechanical potential energy that can enable water to flow.

If no circuit is connected to a battery, or if a switch connecting a circuit is open, no electrical current will flow. But the potential still exists, as there will be a voltage across the batter terminals. If a water pump is running but a valve connecting a piping system is closed, no water will flow. But the potential still exists, since the pump supplies mechanical pressure upstream of the valve. In this sense, mechanical pressure (mechanical potential) is analogous to electrical voltage (electrical potential).

When the battery is connected to a closed circuit, current will flow. The current will encounter electrical resistance causing voltage to drop (a loss in potential energy). The loss of potential energy in the resistor equals the heat generated by the resistor. This is the basis of Kirchhoff’s voltage law, which states the algebraic sum of the voltages in a closed circuit equals zero. It is basically a statement of conservation of energy.

When the water valve is opened water will flow. The water flow will encounter pipe resistance resulting it water pressure to drop (a loss in mechanical potential energy) along the length of the pipe.

Hope this helps.

We can consider almost all concepts By water in tank.As water in pipe as electrons , tank as battery or energy source , Pressure difference as potential difference ,resistors as changed area of cross section of pipe etc.In images,the Charges are moving From higher point to lower points,this difference is potential difference

Images by eugene

I think it is a measure of how much energy it takes to move a charge over a certain path.

A voltage difference of 1 volt means that you gain 1 joule if you move 1 Coulomb of charge between the electrodes from plus to minus. A resistor exerts friction on charge carriers, so if this charge is moved through a resistor, this energy will appear as heat in the resistor. If you move the charge through vacuum, the energy will appear as kinetic energy at the low voltage electrode.

In case of alternating voltage, which is always sinusoidal, 1 volt means that the mean square voltage is 1 volt so the amplitude of sinusoidal time dependent voltage is $$\sqrt{2}$$ volt.

In short, this arose from a hydrodynamic analogy: the electrostatic potential is similar to pressure, the electrical resistance is similar to the hydraulic resistance of the pipe, the electric current is similar to the flow rate of a liquid. Battery voltage similar to hydraulic head. More details on this concept can be found in Maxwell’s article On Faraday's Lines of Force