A combination of capacitors is set up as shown in the figure. The magnitude of the electric field, due to a point charge Q (having a charge equal to the sum of the charges on the 4 μF and 9 μF capacitors), at a point distant 30 m from it, would equal :
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JEE Main 2016 · 3 Apr · Shift 1, Physics question 13

Answer and worked solution
Official answer: C
3 μF and 9 μF in parallel make 12 μF, and in series with 4 μF that gives 3 μF across 8 V: 24 μC. The 4 μF capacitor holds 24 μC. The 12 μF pair is at 2 V, so the 9 μF holds 18 μC. Then Q = 42 μC and