Multimeter Polarity Test for Components
In resistance mode, a multimeter applies an internal test voltage; reversing probes reverses device bias, so a healthy diode shows strongly asymmetric indications while an ohmic metal wire or resistor is approximately polarity independent.
Why this shows up in the exam
Diode polarity identification · Continuity checks · Distinguishing a resistor from a junction device
Learn the idea
Reversing an ohmmeter's probes distinguishes polarity-sensitive junctions from approximately symmetric resistive components. An ohmmeter contains a source. A diode conducts far more in one probe direction than the other, while an ordinary metal resistor gives essentially the same reading both ways.
🧠 Memory hook: Same both ways suggests a resistor; one-way conduction suggests a diode.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- R_indicated approximately V_test/I_test — conceptual basis of resistance-mode indication
- R_forward much less than R_reverse — expected qualitative diode polarity test away from breakdown
How to approach it
- 1Identify the meter mode
- 2Predict what probe reversal changes physically
- 3Separate symmetric conductors from junction devices
Common slip-ups that cost marks
- •Testing a powered circuit in resistance mode
- •Expecting ideal zero and infinite readings from every real diode
- •Ignoring parallel circuit paths
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
In a meter bridge, resistance 2 ohm is in the left gap and balance occurs at 40 cm from the left end. Find the right-gap resistance.
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