Overview
This lecture explains the equation ( V = IR ), explores how voltage, current, and resistance relate, and reviews current vs. potential difference graphs for various components.
The ( V = IR ) Equation
- ( V = IR ) means potential difference (voltage) equals current times resistance.
- To find voltage: multiply current (I) by resistance (R); example: ( 4A \times 2\Omega = 8V ).
- To find resistance: rearrange to ( R = V/I ); example: ( 24V / 8A = 3\Omega ).
Relationships and Graphs
- If resistance is constant, current increases proportionally with voltage and vice versa.
- A graph of current vs. potential difference (for wires/resistors) forms a straight line through the origin.
- Negative graph values indicate reversal of battery direction, showing negative voltage and current.
- Steeper graph lines correspond to lower resistance; flatter (less steep) lines indicate higher resistance.
Factors Affecting Resistance
- If temperature increases, resistance increases; thus, higher currents can heat wires and alter resistance.
- In real circuits, high currents may cause temperature rise and deviation from perfect straight-line graphs.
Non-Ohmic Components (Filament Lamps & Diodes)
- Filament lamps (light bulbs) have a wire that heats up, increasing resistance, causing the graph to curve (less steep at higher currents).
- Diodes allow current only in one direction, showing current only when potential difference is positive due to high resistance in reverse.
Key Terms & Definitions
- Potential Difference (Voltage, V) — The energy transferred per unit charge in a circuit.
- Current (I) — The flow of electric charge, measured in amperes (A).
- Resistance (R) — Opposition to current flow, measured in ohms (Ω).
- Ohm’s Law — The statement of ( V = IR ) relating voltage, current, and resistance.
- Filament Lamp — A bulb with a heated metal wire; resistance increases with current.
- Diode — A component permitting current to flow in only one direction.
Action Items / Next Steps
- Practice calculating voltage, current, and resistance using ( V = IR ).
- Sketch current vs. potential difference graphs for resistors, filament lamps, and diodes.