Arrange the following in the order of their resistance:
(A) Ammeter of range 0 to 1 A
(B) Milli-ammeter of ran

Question

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 μA
(D) Voltmeter of range 0 to 100 V

Accepted Answer

1. **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. 2. **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: $500$ μA $= 0.0005$ A Since $I_A > I_B > I_C$, the resistance order is $R_A < R_B < R_C$. 3. **Conclusion:** Combining these, the order of resistance is Voltmeter > Micro-ammeter > Milli-ammeter > Ammeter ($D > C > B > A$).

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