4.3 Parallel Circuits, Dividers & Smart Sensors
Syllabus: 4.3.2 (10) • 4.3.3 (2, 3) • 4.3.1 (LDR/Thermistor)
🚗 The Hook: Why Does Traffic Flow Faster with More Lanes?
Imagine a busy motorway with a single lane - traffic crawls! Now open a second lane. Does the journey get harder or easier? Easier, right! The same logic applies to parallel resistors. More paths = less resistance = more current can flow.
👶 Baby Steps: Understanding Parallel Resistance
The Key Idea: In parallel, current has MULTIPLE pathways. It doesn't have to squeeze through just one resistor - it can split up!
The Result: Total resistance decreases. In fact, it's ALWAYS less than the smallest resistor in the group.
The Formula: For two resistors: RT = (R₁ × R₂) ÷ (R₁ + R₂) ... that's Product over Sum!
🚦 Interactive: The Traffic (Current) Analogy
📝 The Formula Triangle
RT = Product ÷ Sum
Cover what you want → Do what you see!
⚠️ Examiner's Trap
DON'T: Add parallel resistors like series! (6Ω + 3Ω ≠ 9Ω total)
DO: Use Product ÷ Sum: (6 × 3) ÷ (6 + 3) = 18 ÷ 9 = 2Ω
REMEMBER: The answer is ALWAYS smaller than the smallest resistor!
📋 Syllabus Checklist
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