The ammeter your physics instructor uses for in-class demonstrations has a resistance R_g = 60 $\varOmega$ and requires a current of 1.0 mA for full-scale deflection.The same ammeter can be used to measure currents of much greater values by wiring a shunt resistor of relatively small resistance,R_p ,in parallel with the ammeter.The value of the shunt resistance that allows the ammeter to be used to measure a current of 12 A at full-scale deflection is A)5.0 m$\varOmega$. B)4.0 m$\varOmega$. C)3.5 m$\varOmega$. D)2.5 m$\varOmega$. E)1.7 m$\varOmega$.

Question

Quizplus · Accepted Answer

To measure 12 A, the shunt resistor R_p must bypass most of the current. Using the formula R_p = (R_g * I_g) / (I - I_g), where I_g = 1 mA and I = 12 A, we find R_p = (60 $\varOmega$ * 0.001 A) / (12 A - 0.001 A) ≈ 5.0 m$\varOmega$.

The Ammeter Your Physics Instructor Uses for In-Class Demonstrations Has Ω\varOmegaΩ

The Ammeter Your Physics Instructor Uses for In-Class Demonstrations Has $\varOmega$