Ohm's Law Fundamentals
Ohm's Law defines the relationship between voltage (V), current (I), and resistance (R):
V = I × R
The three derived forms are:
| Find | Formula |
|---|---|
| Voltage (V) | V = I × R |
| Current (I) | I = V / R |
| Resistance (R) | R = V / I |
Power Relationships
Electrical power P (watts) can be expressed in three equivalent forms:
| Formula | When to Use |
|---|---|
| P = V × I | Know voltage and current |
| P = I² × R | Know current and resistance |
| P = V² / R | Know voltage and resistance |
Worked Example
A 12 V battery powers a resistive load of 47 Ω:
- Current: I = 12 / 47 ≈ 0.255 A
- Power: P = 12 × 0.255 ≈ 3.06 W
Series vs Parallel Circuits
Series: Total resistance increases — R_total = R₁ + R₂ + R₃
Parallel: Total resistance decreases — 1/R_total = 1/R₁ + 1/R₂ + 1/R₃
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