Calculate resistance (Ohms) using Ohm's Law: R = V/I or R = V²/P. Essential for electronics, circuit design, and resistor selection.
📊 Calculated Resistance
0 Ω
R = V / I = 220V ÷ 2A = 110 Ohms
⚡ Ohm's Law Triangle
R = V / I | V = I × R | I = V / R Also: P = V × I | R = V² / P | P = I² × R
📖 What is Electrical Resistance?
Electrical resistance is the opposition to current flow in an electrical circuit. It is measured in Ohms (Ω). Higher resistance means less current for the same voltage. Resistance is a fundamental property of materials - conductors like copper have low resistance, while insulators like rubber have very high resistance.
📐 Resistance Formulas (Ohm's Law)
R = V / I (Resistance = Voltage ÷ Current) R = V² / P (Resistance = Voltage² ÷ Power)
📊 Common Resistance Values Reference Table
Component / Device
Typical Resistance (Ω)
At Voltage/Current
Application
100W Light Bulb (220V)
484 Ω
220V, 0.45A
Home lighting
Heating Element (1500W)
32.2 Ω
220V, 6.8A
Water heater, iron
LED with Resistor
100-300 Ω
5V, 20mA
Indicator lights
Human Body (dry skin)
100,000 - 1,000,000 Ω
-
Safety reference
Speaker (audio)
4 Ω, 8 Ω, 16 Ω
-
Audio systems
USB Cable
0.1 - 0.5 Ω
-
Charging
🔧 How to Measure Resistance with a Multimeter
Set multimeter to Ω (Ohms) mode
Turn off circuit power - never measure resistance on a live circuit!
Connect probes across the resistor or component
Read the resistance value from the display
For in-circuit measurement, one leg may need to be disconnected for accuracy
Electrical resistance is the opposition to current flow in a circuit. Measured in Ohms (Ω), it determines how much voltage is needed to push a given current. Higher resistance means less current for the same voltage. Copper wire has very low resistance (good conductor), rubber has very high resistance (insulator).
❓ How do I calculate resistance using Ohm's Law? ▼
Using Ohm's Law: R = V / I, where R is resistance in Ohms, V is voltage in Volts, and I is current in Amperes. For example, R = 220V ÷ 2A = 110Ω. Alternatively, R = V² / P when power is known. Example: R = (220V)² ÷ 100W = 48,400 ÷ 100 = 484Ω.
❓ What is the difference between series and parallel resistance? ▼
In series: Total resistance = R₁ + R₂ + R₃... (resistance adds up, total is larger than any individual). In parallel: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃... (total resistance is less than the smallest resistor). Example: Two 100Ω resistors in series = 200Ω; in parallel = 50Ω.
❓ What does the resistor color code mean? ▼
Resistors use colored bands to indicate their resistance value. The first two bands represent digits, the third band is the multiplier (number of zeros), and the fourth band indicates tolerance (Gold=±5%, Silver=±10%). For example: Brown-Black-Red-Gold = 10 × 100 = 1000Ω (1kΩ) ±5%.
❓ How to measure resistance with a multimeter? ▼
Set multimeter to Ω (Ohms) mode. Turn off circuit power (never measure resistance on live circuit). Connect probes across the resistor. Read the value. For in-circuit measurement, one leg may need to be disconnected for accuracy.
❓ What is a thermistor? ▼
A thermistor is a temperature-sensitive resistor. PTC (Positive Temperature Coefficient) resistance increases with temperature (used in overcurrent protection). NTC (Negative Temperature Coefficient) resistance decreases as temperature rises (used in temperature sensors).
💡 Educational Note: Resistance is measured in Ohms (Ω), named after German physicist Georg Simon Ohm (1789-1854). One Ohm is defined as the resistance that allows one Ampere of current to flow when one Volt of electrical pressure is applied.