Which of the following will NOT be observed when a multimeter (operating in resistance measuring mode) probes connected across a component, are just reversed?
- (A)Multimeter shows a deflection, accompanied by a splash light out of connected component in one direction and NO deflection on reversing the probes if the chosen component is LED.
- (B)Multimeter shows NO deflection in both cases i.e. before and after reversing the probes if the chosen component is metal wire.
- (C)Multimeter shows NO deflection in both case i.e. before and after reversing the probes if the chosen component is capacitor.✓ Correct
- (D)Multimeter shows an equal deflection in both cases i.e. before and after reversing the probes if the chosen component is resistor.
Answer: (C)
Solution
A multimeter in resistance mode drives a small current from its internal cell through whatever is bridged by its probes. Across an LED the current passes only when the diode is forward biased, so one orientation gives a deflection, often with a faint flash from the junction, and reversing the probes gives none. Across a plain metal wire the resistance is the same either way, so the reading does not change on reversal. Across an ordinary resistor the behaviour is symmetric too, giving equal deflection in both orientations. A capacitor, however, does not sit still: on first contact it draws a brief charging current and the needle flicks, and on reversing the probes it discharges and then charges with the opposite polarity, flicking again. The claim that a capacitor shows no deflection in either orientation is therefore the one behaviour that cannot be observed.
JEE Main · 2020 · 03 Sep 2020 · Shift 2 · Single correct option