Ohm's Law Lecture Notes

Introduction to Electrical Resistance

• Definition: Electrical resistance is the property of a substance that slows down the movement of electrons and converts electrical energy into other forms of energy.
• Measurement Unit: Resistance is measured in ohms (Ω).
• Measurement Tool: An ohmmeter can be used to measure resistance.

Resistors

• Definition: A resistor is a component in a circuit with a specific resistance.
• Purpose: Resistors control current or voltage to suit the needs of other electronic devices in the circuit.

Types of Resistors

• Ohmic Resistors:

  • Do not change resistance with temperature.
  • Obey Ohm's Law.
  • Graph of voltage vs. current is a straight line.

• Non-Ohmic Resistors:

  • Do not obey Ohm's Law.
  • Example: Light bulbs, where resistance changes with temperature.
  • Have variable resistance values.

Ohm’s Law

• Mathematical Equation: Shows the relationship between voltage (V), current (I), and resistance (R).

  [ R = \frac{V}{I} ]

• Symbols:

  • R = Resistance
  • V = Voltage
  • I = Current

Calculating Resistor Values

• Resistor values can be determined by calculation or by plotting experimental data.
• Measure the slope of the V/I graph to find resistance.

Example Calculation

• Problem Statement: Calculate the voltage drop across a bulb with a resistance of 144 ohms and a current of 0.50 A.

Given:

• Resistance (R): 144 Ω
• Current (I): 0.50 A

Calculation:

• Voltage (V) = Current (I) × Resistance (R)

[ V = 0.50 , \text{A} \times 144 , \Omega = 72 , \text{V} ]

Answer:

• The voltage drop across the bulb is 72 volts.