Ammeter question?

Question

what is the resistance that must be placed in parallel with a 25.0 ohm galvanometer having a 50.0 uA sensitivity to allow it to be used as an ammeter with a 10.0 A full scale reading.

Answer 1

Voltage FS = 50uA x 25Ω = 1.25mv

R = E/I = 1.25mv/10a = 0.125mΩ = 125µΩ

125µΩ is sufficiently small compared to 25Ω that we don't need to consider the effect of their parallel combination.

.

Answer 2

!0-0.00005 = 9.99995 amps bypassed.

Voltage to drive meter to full scale = 0.00125 volts {(E = IXR) or 0.00005 X 25}

R = E/I or 0.00125/9.99995 = 0.000125ohms or 125 microhms (shunt)