# Analogies for internal resistance and emf

• The_Lobster
In summary, the potential difference decreases when there is an internal resistance in the source of emf.
The_Lobster
Hi!

I'm trying to fully grasp why the potential drops when an internal resistance is present in a source of emf. At first I thought that yes it would be harder to "push" the charges to the higher potential, but once there, why shouldn't the higher potential be the same as before? Just as if a water pump was to push water to the top of a fountain, if there was resistance in this path, it would go slower, but the top of the fountain would still be at he same height, and the potential energy of the water the same once it reaches the top?

J

edit: could one think of this way: the internal resistance decreases current, thus in the water fountain analogy, the water doesn't reach the same height it would do had it not been for the internal resistance, and since the height is lower, the potential is lower.

Last edited:
Hi The_Lobster!
The_Lobster said:
edit: could one think of this way: the internal resistance decreases current, thus in the water fountain analogy, the water doesn't reach the same height it would do had it not been for the internal resistance, and since the height is lower, the potential is lower.

Yes, that's correct …

in the water analogy, you could fix the height, but in emf there is no height (or anything else) to fix, so you end up with a lower potential (which in the case of water means lower height).

(ok, now try using a water analogy to explain energy storage in a capacitor! )

Great! Thanks! :D

On a molecular level, could one say that since the current decreases (due to the internal resistance), the electric field on which the potential difference is based becomes weaker?

hmm … not sure what the molecular level has to do with it (and there's a potential difference whether there's a current flowing or not) …

if the potential difference is lower, then the field must be lower.

Right! Thank you again! :)

## 1. What is internal resistance?

Internal resistance refers to the resistance within a battery or circuit that hinders the flow of current. It is caused by the material and structure of the battery or circuit components.

## 2. What is emf?

EMF, or electromotive force, is the voltage generated by a power source such as a battery. It is the driving force that pushes electrons through a circuit.

## 3. How are internal resistance and emf related?

Internal resistance and emf are inversely proportional to each other. This means that as the internal resistance increases, the emf decreases.

## 4. What is an analogy for internal resistance and emf?

One analogy for internal resistance and emf is a garden hose. The internal resistance can be compared to the diameter of the hose, as a larger diameter will allow more water to flow through. The emf can be compared to the water pressure, as a higher pressure will push more water through the hose.

## 5. How can internal resistance affect the performance of a circuit?

A high internal resistance can cause a voltage drop and reduce the amount of current flowing through the circuit. This can lead to decreased performance and efficiency of the circuit.

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