52. Voltage, Current, and Resistance (V = IR)

1. The Ohm’s Law Equation

The formula V = IR relates these three key electrical properties:

• V (Potential Difference/Voltage): Measured in Volts (V).

• I (Current): Measured in Amperes (A).

• R (Resistance): Measured in Ohms (Ω).

Example Calculations

• To find Voltage: If a circuit has a current of 4A and a resistance of 2Ω then V = 4 x 2 = 8V

• To find Resistance: If a 24V battery produces a current of 8A, rearrange to R = V / I. Therefore, $R = 24 / 8 = 3Ω

2. IV Graphs (Current vs. Potential Difference)

An IV graph displays how current changes as the potential difference across a component is varied. The shape of the graph tells us about the nature of the component.

Fixed Resistors and Wires

• The Shape: A straight line passing through the origin.

• The Relationship: Current is directly proportional to potential difference, provided the temperature remains constant.

• Steepness: A steeper line indicates a lower resistance, while a shallower line indicates a higher resistance.

Filament Lamps (Light Bulbs)

• The Shape: An "S" shaped curve that flattens out at higher voltages.

• The Reason: As current increases, the metal filament heats up. This increase in temperature causes the resistance to rise, making it harder for current to flow as the voltage increases further.

Diodes

• The Shape: No current flows for negative or very low voltages, followed by a sharp increase in current.

• The Reason: Diodes only allow current to flow in one direction. They have extremely high resistance when current tries to flow the "wrong" way.

3. Summary of Component Characteristics