NEET2021PhysicsMagnetic Effects of CurrentActual
A uniform conducting wire of length 12 a and resistance R is wound up as a current-carrying coil in the shape of, (i) an equilateral triangle of side a . (ii) a square of side a . The magnetic dipole moments of the coil in each case respectively are:
Options
- A3 I a 2  and  3 I a 2
- B3 I a 2  and   I a 2
- C3 I a 2  and  4 I a 2
- D4 I a 2  and  3 I a 2
Correct answer
A. 3 I a 2  and  3 I a 2
Step-by-step solution
Area of equilateral triangle of side a, A = 1 2 × a × 3 a 2 = 3 4 a 2 Magnetic moment of each triangle, m = I A = 3 4 a 2 I 12   a length of wire will form 4 loops of triangle of side a . Magnetic moment of triangle, M 1 = N m = 4 × 3 4 a 2 I = 3 I a 2 Similarly, magnetic moment of square M 2 = N m = 3 × I a 2 = 3 I a 2