WAEC Physics 2012 Objective — Question 42

Question 42 of 50 from the West African Examinations Council (WAEC) Physics 2012 Objective paper, with the correct answer and a full explanation.

An ammeter with a full scale deflection of 10mA has internal resistance 0.5Ω. Calculate the resistance of the shunt required to adapt it to read up to 3A.

A. A. 0.0017ΩCorrect
B. B. 0.0130Ω
C. C. 0.0250Ω
D. D. 0.1000Ω

Explanation

Resistivity/shunt formula: Rs x Is = Ig x Rg, where Ig=0.01A, Rg=0.5Ω, Is = 3-0.01 = 2.99A. Rs = (Ig x Rg)/Is = (0.01x0.5)/2.99 = 0.0017Ω.

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