Solved: PHYSICS Question for NEET

NEET PHYSICSMedium

Arrange the following in the order of their resistance: (A) Ammeter of range 0 to 1 A (B) Milli-ammeter of range 0 to 100 mA (C) Micro-ammeter of range 0 to 500 \mu A (D) Voltmeter of range 0 to 100 V

A > B > C > D

D > C > B > A

D > A > B > C

C > B > A > D

Step-by-Step Solution

Voltmeter vs Ammeter: A voltmeter requires a very high resistance (galvanometer resistance + large series resistance) to ensure it draws negligible current (NCERT Physics Class 12, Eq. 4.28). An ammeter requires a very low resistance (galvanometer resistance in parallel with a small shunt) to ensure negligible voltage drop (NCERT Physics Class 12, Section 4.10). Thus, the voltmeter (D) has the highest resistance.
Ammeters Ranges: For an ammeter, the equivalent resistance is approximately equal to the shunt resistance $r_s$ . The shunt resistance is inversely proportional to the current range $I$ (since $r_s \approx I_g R_g / I$ ).

Range A: $1$ A
Range B: $100$ mA $= 0.1$ A
Range C: $500$ \mu A $= 0.0005$ A Since $I_A > I_B > I_C$ , the resistance order is $R_A < R_B < R_C$ .

Conclusion: Combining these, the order of resistance is Voltmeter > Micro-ammeter > Milli-ammeter > Ammeter ( $D > C > B > A$ ).

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