Two thick wires and two thin wires, all of the same materais and same length from a square in the three differenct ways, `P,Q` and `R` as shwon in figure with current connection shown, the magneitc feidl at the centre of the square is zero in cases.

Options

A. In P only
B. In P and Q only
C. In Q and R only
D. P and R only

Answer

D

Explanation

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.