Final answer:
To find the internal resistance of a car battery, use the formula ε - Ir = Vterminal, where ε is the electromotive force, I is the current, and r is the resistance. This requires accurate measurements of battery emf, terminal voltage, and current.
Step-by-step explanation:
To determine the internal resistance of a car battery, we can use the relationship between electromotive force (emf), terminal voltage, internal resistance, and current. Given the emf (ε) of the battery, terminal voltage (Vterminal), and the current (I), we can use the formula:
Vterminal = ε - Ir
Where:
- ε is the electromotive force of the battery
- I is the current flowing through the circuit
- r is the internal resistance of the battery
This formula tells us that as the current increases, the terminal voltage decreases due to the potential drop across the internal resistance. To solve for the internal resistance (r), we can rearrange the formula:
r = (ε - Vterminal) / I
For example, if the battery has an emf of 12.0 V, and when a current of 8.00 A is applied, the terminal voltage is 15.0 V (this usually indicates charging, where the terminal voltage is higher than the emf), we can calculate the internal resistance as follows:
r = (12.0 V - 15.0 V) / 8.00 A
However, the given values are not consistent with typical operation (where the terminal voltage is less than the emf during discharge) and might be a typo or misunderstanding in the question. It's important to ensure values are accurate before performing calculations.