1. What is Internal Resistance?

Internal resistance is the opposition to current flow within a voltage source itself. All real-world power sources (batteries, generators, etc.) have some internal resistance that causes voltage drop under load.

2. How Does the Calculator Work?

The calculator uses the internal resistance formula:

Where:

• \( R_{int} \) — Internal resistance (ohms)
• \( V_{oc} \) — Open circuit voltage (volts)
• \( V_l \) — Loaded voltage (volts)
• \( I \) — Current (amps)

Explanation: The formula calculates the internal resistance by measuring the voltage drop from no-load to loaded condition and dividing by the current drawn.

3. Importance of Internal Resistance Calculation

Details: Knowing internal resistance is crucial for battery testing, power supply design, and understanding voltage regulation. Lower internal resistance indicates better power source performance.

4. Using the Calculator

Tips: Measure open circuit voltage with no load, then measure voltage under load with known current. All values must be positive and current must be greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: Why does internal resistance matter?
A: Internal resistance affects voltage regulation, power delivery capability, and efficiency of power sources.

Q2: What are typical internal resistance values?
A: For AA batteries: 0.1-0.3 ohms; Car batteries: 0.005-0.02 ohms; Lithium-ion: 0.05-0.2 ohms (varies with chemistry and age).

Q3: How does temperature affect internal resistance?
A: Internal resistance generally decreases with increasing temperature and increases as temperature drops.

Q4: Does internal resistance change over time?
A: Yes, internal resistance increases as batteries age and degrade, making it a useful indicator of battery health.

Q5: Can internal resistance be too low?
A: Extremely low internal resistance can lead to high short-circuit currents, requiring proper protection circuits.