WAEC Physics 2011 Paper

Concept:A shunt is a low resistance connected in parallel with the ammeter to carry the excess current.Explanation:Full-scale deflection current, $I_g = 10\,\text{mA} = 0.01\,\text{A}$.Current to be measured, $I = 3\,\text{A}$.Therefore, current through the shunt is $I_s = I - I_g = 3 - 0.01 = 2.99\,\text{A}$.For a parallel connection, the voltage across the meter equals the voltage across the shunt:$I_g R_g = I_s R_s$.So, $R_s = \dfrac{I_g R_g}{I_s}$.Substitute the values:$R_s = \dfrac{0.01 \times 5}{2.99} = 0.0167\,\Omega$.Answer:The required shunt resistance is $0.0167\,\Omega$, which is option A.