Question

Two thick wires and two thin wires, all of the same materials and same length from a square in the three different ways $P,Q$ and $R$ as shown in figure with current direction shown, the magnetic field at the centre of the square is zero in cases

• A. in $P$ only
• B. in $P$ and $Q$ only
• C. in $Q$ and $R$ only
• D. $P$ and $R$ only

Answer 1

The correct option is D $P$ and $R$ only

In $P$ and $R$ loops, currents are divided in same properties because the branches have equal resistance. Hence magnetic field produced at centre due to each segment is of equal magnetic but of opposite direction, so net field is zero.