Electricity & Magnetism · AP Physics 2 (DC Circuits)
Ohm's Law & Volt-Ampere Resistance Measurement Simulator
Key exam takeaway: "Large-Internal-High, Small-External-Low". Use internal wiring for large resistances (R_meas > R_true) and external wiring for small resistances (R_meas < R_true).
- Client-side
- No Sign-up
- Live Derivation
- Projector Mode
- Print Worksheet
3D Simulation Stage● 60 FPS
Parameter Controls
Ω
Ω
Ω
Live Derivations & Metrics
Measured Resistance R_meas
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Relative Systematic Error
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Critical Threshold sqrt(RA*RV)
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Recommended Wiring
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Real-Time Formula Derivation
Governing Formula:
--Substitution:
--Regime: --
Related Tool:
⚡ Standard Tool: Ohm's Law Calculator ↗
Worked Examples & Exam Question Deep Dive
Worked Problem
Problem: Rx ≈ 10Ω, RA = 0.2Ω, RV = 2000Ω. Choose internal or external wiring. Does it read high or low?
Step-by-Step Derivation:
- Critical R0 = sqrt(0.2*2000) = 20Ω. Since Rx < 20Ω (small resistor), select external wiring. Voltmeter current diversion makes R_meas read low.
Worked Problem
Problem: A conductor passes 0.5A at 6V. What is its resistance? What if voltage drops to 0V?
Step-by-Step Derivation:
- R = 6/0.5 = 12Ω. At 0V, resistance remains 12Ω! Resistance is an intrinsic physical property independent of voltage.
Student Inquiry Worksheet & Practice Problems
Q1. Variant 1: In testing I vs U relationship, what parameter must be kept constant? What is the rheostat's function?
Answer Key: Resistor value R must be constant. Rheostat protects the circuit and modulates voltage to gather multiple test points.
Q2. Variant 2: How does the "touch test" empirical method identify optimal wiring without knowing meter resistances?
Answer Key: Toggle the voltmeter lead across the ammeter: if current changes significantly, choose internal; if voltage changes significantly, choose external.
Q3. Variant 3: A uniform wire is folded in half and twisted together. What is the new resistance ratio?
Answer Key: 1/4 original! Length halves (L/2) and cross-section doubles (2S), yielding R' = 1/4 R via R = ρL/S.
Frequently Asked Questions & Misconceptions
Does Ohm's law apply universally? When does it fail?
Strictly for ohmic resistors. It fails for non-ohmic devices (motors, electrolysis cells, diodes) where electrical energy converts to work or chemistry.
Why does volt-ampere measurement always carry systematic error? How to achieve zero error?
Real meters are non-ideal. True zero-error measurement requires a Wheatstone bridge or Kelvin 4-wire sensing.
How does temperature affect metal vs semiconductor resistance differently?
Metals have positive temperature coefficient (PTC, R rises with heat). Semiconductors have negative coefficient (NTC, R drops exponentially).
What is typical human body resistance? Why is 36V the legal safety threshold?
Wet human skin drops to ~1000Ω. Lethal threshold is ~30mA. U = IR = 30mA * 1000Ω = 30V, establishing the 36V safety ceiling.