Overview
This lecture covers the use of resistors in circuits, application of Ohm's Law, and calculation of electrical power in resistive components.
Resistors and Resistance
- A resistor is a circuit element that resists the flow of electric charge (current).
- Higher resistance causes lower current for the same voltage.
- Resistance is measured in ohms (Ω); common units include ohms, kilo-ohms (kΩ), and mega-ohms (MΩ).
- Current enters the positive terminal of a resistor and exits the negative terminal.
Ohm's Law
- Ohm's Law relates voltage (V), current (I), and resistance (R) with the formula: V = R × I.
- Current can be found with I = V / R.
- Resistance can be found with R = V / I.
- The Ohm's Law triangle helps remember the relationships among V, I, and R.
Example: Using Ohm's Law
- For a 2.2 kΩ resistor with 5V across it: I = 5 V / 2.2 kΩ = 2.27 mA (milliamps).
- This calculation demonstrates that knowing any two values allows you to find the third using Ohm's Law.
Power in Resistors
- Power (P) in a resistor is always absorbed (not supplied) and is usually converted to heat.
- Power formulas:
- P = V × I
- P = I² × R
- P = V² / R
Example: Calculating Power
- For a 470 Ω resistor with 3 mA current:
- Power: P = (3 mA)² × 470 Ω = 4.23 mW (milliwatts)
- Voltage across resistor: V = 470 Ω × 3 mA = 1.41 V
- Power can also be found by P = V × I = 1.41 V × 3 mA = 4.23 mW
Key Terms & Definitions
- Resistor — A component that limits or resists electric current flow.
- Resistance (R) — A measure of a material's opposition to current, measured in ohms (Ω).
- Ohm's Law — The fundamental relationship V = R × I for resistive circuits.
- Power (P) — The rate at which energy is absorbed or dissipated, measured in watts (W).
Action Items / Next Steps
- Practice using Ohm's Law and power formulas with different resistor values and circuit scenarios.
- Review standard resistor values and unit conversions (ohms, kilo-ohms, mega-ohms).
- Prepare questions for the next lesson if any concepts remain unclear.