Application of Ohm’s Law
Ohm’s Law is the single most-used formula in electronics. It describes the mathematical relationship between voltage, current, and resistance, named after the German physicist Georg Simon Ohm (1789–1854).
Ohm’s Law Statement
Voltage (V) = Current (A) × Resistance (Ω) — rearranges to I = V/R and R = V/I
The Ohm’s Law Triangle
Worked Examples
Example 1: Find current
Formula: I = V / R
Substitute: I = 5 / 220 = 0.0227 A
Answer: I ≈ 22.7 mA
Meaning: Current through a 220 Ω resistor powered by a 5 V Arduino pin.
Example 2: Find resistance needed (LED circuit)
Voltage across resistor = 5 – 2 = 3 V
R = V / I = 3 / 0.020 = 150 Ω
Answer: Use nearest standard value — 150 Ω or 180 Ω
Example 3: Find voltage
V = I × R = 0.05 × 100 = 5 V
Answer: V = 5 V
Series Circuits
RT = 100 + 150 = 250 Ω
I = 5 / 250 = 0.02 A = 20 mA
V1 = 0.02 × 100 = 2 V
V2 = 0.02 × 150 = 3 V
Check: 2 + 3 = 5 V ✓
Parallel Circuits
1/RT = 1/200 + 1/300 = 5/600 → RT = 120 Ω
IT = 6 / 120 = 50 mA
I1 = 6 / 200 = 30 mA
I2 = 6 / 300 = 20 mA
Check: 30 + 20 = 50 mA ✓
Using a Multimeter
| Measurement | Procedure | Important note |
|---|---|---|
| Voltage (V) | Set to VDC. Red probe on +, black on GND. | Connect in parallel with the component. |
| Resistance (Ω) | Set to Ω. Disconnect component. Touch probes to both ends. | Power MUST be off. |
| Current (A) | Set to DC Amps. Break circuit and insert multimeter in series. | Wrong connection blows the fuse. |
| Continuity | Set to continuity symbol. Touch probes. Beep = connected. | Useful for checking wire connections. |
Power and Ohm’s Law Together
| Formula | Description | When to use |
|---|---|---|
| P = V × I | Direct power formula | P in Watts, V in Volts, I in Amps |
| P = I² × R | Power from current and resistance | Useful when V is unknown |
| P = V² / R | Power from voltage and resistance | Useful when I is unknown |
Check Your Understanding — Lesson 1.2
You may also like
Nyereka Tech and Tumba College Explore Opportunities for Collaboration
The Launch of our IoT Innovation Hub
