Ohm's Law Lecture Notes

Introduction

• Presenter: Paul from theengineeringmindset.com
• Focus: Understanding and applying Ohm's Law
• Includes: Two problems to test knowledge

What is Ohm's Law?

• Relationship between voltage, current, and resistance
• Developed by German physicist Georg Ohm
• Ohm's experiments involved measuring current by physical sensation

Formulas for Ohm's Law

• Voltage (V) = Current (I) × Resistance (R)
• Current (I) = Voltage (V) ÷ Resistance (R)
• Resistance (R) = Voltage (V) ÷ Current (I)
• Use "Ohm's Triangle" (V-I-R) to easily remember formulas
• Free PDF guide available for download

Ohm's Triangle Method

• Draw a triangle with V on top
• Cover the letter you need to find:
  • For V = I × R (voltage)
  • For I = V ÷ R (current)
  • For R = V ÷ I (resistance)

Understanding the Symbols

• I for current derives from "intensité du courant"
• A for Ampere, named after Andre Ampere
• E may replace V, stands for Electromotive Force (EMF)

Examples and Practice

Finding Voltage

• Example: Circuit with unknown battery voltage
  • Resistor: 3 Ohms
  • Current: 2 Amps
  • Calculation: V = I × R = 2 Amps × 3 Ohms = 6 volts
  • Doubling voltage doubles current (directly proportional)

Finding Current

• Example: 3 Amp lamp with 6 volt power supply
  • Calculation: I = V ÷ R = 6 volts ÷ 3 Ohms = 2 Amps
  • Doubling resistance reduces current by half (inversely proportional)

Finding Resistance

• Example: 12 volt power supply with unknown resistance
  • Current: 0.5 Amps
  • Calculation: R = V ÷ I = 12 volts ÷ 0.5 Amps = 24 Ohms

Key Relationships

• Current is directly proportional to voltage
• Current is inversely proportional to resistance

Practical Applications

• Voltage pushes electrons through circuits
• Resistance controls the flow of electrons
• Increasing voltage or decreasing resistance increases current

Practice Problems

1. Lamp with 240 Ohms resistance in the US (120 volts): Find current
2. Same lamp in the UK, current 0.958 Amps: Find voltage

Conclusion

• Links to answers and solutions available
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