1. What is Internal Resistance?

Internal resistance (r) is the opposition to the flow of current within a voltage source itself. It causes voltage drop when current flows and explains why cell voltage decreases under load.

2. How Does the Calculator Work?

The calculator uses the internal resistance formula:

Where:

• \( r \) — Internal resistance (Ω)
• \( \Delta V \) — Change in voltage (V)
• \( \Delta I \) — Change in current (A)

Explanation: The equation shows that internal resistance equals the change in voltage divided by the change in current when the load changes.

3. Importance of Internal Resistance Calculation

Details: Knowing internal resistance helps predict real-world battery performance, calculate maximum power transfer, and understand voltage drop under load.

4. Using the Calculator

Tips: Measure voltage and current at two different load conditions. Enter the differences (ΔV and ΔI) in the calculator. Both values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: How do you measure ΔV and ΔI?
A: Measure voltage and current with two different load resistors, then calculate the differences between the two measurements.

Q2: What are typical internal resistance values?
A: Alkaline AA batteries: ~0.1-0.3Ω; Lithium-ion: ~0.05-0.2Ω; Car batteries: ~0.01Ω.

Q3: Why does internal resistance matter?
A: It limits maximum current, causes voltage drop under load, and affects battery efficiency and heating.

Q4: Does internal resistance change?
A: Yes, it increases as batteries age or discharge, and varies with temperature.

Q5: What's the relationship with maximum power transfer?
A: Maximum power transfer occurs when load resistance equals internal resistance.