# Physics - Internal Resistance

> Source: https://ollybritton.com/notes/a-level/physics/topics/internal-resistance/ · Updated: 2021-04-21 · Tags: school, physics, electricity, year-1

## See Also
- [Physics - Resistance and Ohm's Law](https://ollybritton.com/notes/a-level/physics/topics/ohms-law/)
- [Physics - Voltage and Potential Difference](https://ollybritton.com/notes/a-level/physics/topics/potential-difference/)

## Flashcards
##### If $E$ is the E.M.F. of a battery and $V$ is the terminal voltage, what is the formula for "lost volts"??
$$
Ir = E - IR
$$

##### Why are there "lost volts" in a battery??
Because the battery has some internal resistance.

##### Why do the lights on old-fashioned cars blink out when you start the engine??
The starter motor requires a high current which increases the lost volts due to internal resistance, so all potential difference is conserved.

##### What does $Ir$ represent when talking about internal resistance??
The lost volts.

##### What does $IR$ represent when talking about internal resistance??
The terminal boltage.

### 2022-05-04
##### What is internal resistance in a battery??
Where some voltage is dropped across the battery due to resistances when a current flows.

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