Two thick wires and two thin wires, all of the same materials and same length form a square in the three different ways $P$, $Q$ and $R$ as shown in fig with current connection shown, the magnetic field at the centre of the square is zero in cases
AIn $P$ only
BIn $P$ and $Q$ only
CIn $Q$ and $R$ only
D$P$ and $R$ only
Medium
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D$P$ and $R$ only
d (d) In $P$ and $R$ loops, currents are divided in same proportion because the branches have equal resistance. Hence magnetic field produced at centre due to each segment is of equal magnitude but of opposite direction, so net field is zero.
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