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Question:

A moving coil galvanometer allows a full scale current of 10⁻⁴A. A series resistance of 2MΩ is required to convert the above galvanometer into a voltmeter of range 0-5V. Therefore, the value of shunt resistance required to convert the above galvanometer into an ammeter of range 0-10mA is:

40Ω

10Ω

500Ω

100Ω

Solution:

s'=[Ig/(I−Ig)]G = (I−Ig)/Ig = gsI = Ig(Gs+1)/2I−Ig = 2Ig(Gs)+Ig/200+10⁻⁴G = 5/200G = 5/200/5 = G/40Ω