Q.

A uniform conducting wire of length 12a 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 moment of the coil in each case respectively are             [2021]

1 4Ia2 and 3Ia2  
2 3Ia2 and 3Ia2  
3 3Ia2 and Ia2  
4 3Ia2 and 4Ia2  

Ans.

(2)

For an equilateral triangle of side a :

As total length of the wire =12a

So, number of loops, n=12a3a=4

Magnetic moment of coil, M=nIA                               ...(i)

Area of triangle, A=34a2

From equation (i), M=4I34a2    M=3Ia2

For a square of side a: Area, A=a2

Number of loops, n=12a4a=3

Magnetic moment, M=nIA=3I(a2)=3Ia2