A galvanometer having a resistance of 28.0 has a 1.00- shunt resistance installe

Question

A galvanometer having a resistance of 28.0 has a 1.00- shunt resistance installed to convert it to an ammeter. It is then used to measure the current in a circuit consisting of a 12.0- resistor connected across the terminals of a 20.0-V battery having no appreciable internal resistance. (a) What current does the ammeter measure? (b) What should be the true current in the circuit (that is, the current without the ammeter present)? 1.67 (c) By what percentage is the ammeter reading in error from the true current?

Explanation / Answer

givven resistsnce Rg = 28 ohms

shunt, r = 1 ohm

R = 12 ohm

V = 20 V

a. current measured by ammeter = i

V = i(R + Rg*r/(Rg + r))

hence

i = 1.5425 A

b. true current = I

I = V/R = 1.6667 A

c. %error = (I - i)*100/I = 7.4499%

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