Physics - Internal Resistance
OCR A-Level Physics 2022
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Flashcards
Lost volts
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.
Interpreting Ir and IR
What does $Ir$ represent when talking about internal resistance?
The lost volts.
What does $IR$ represent when talking about internal resistance?
The terminal voltage.
Definition of internal resistance
What is internal resistance in a battery?
Where some voltage is dropped across the battery due to resistances when a current flows.