Q 12-04-106JEE MainJEE Main 2023 (29 Jan, Shift 2)Easy
The electric current in a circular coil of four turns produces a magnetic induction $32\ \text{T}$ at its centre. The coil is unwound and is rewound into a circular coil of single turn, the magnetic induction at the centre of the coil by the same current will be
Answer: (C) $2\ \text{T}$
The wire length is fixed: $4(2\pi r)=2\pi r'\Rightarrow r'=4r$.
$B=\dfrac{\mu_0NI}{2r}$, so $\dfrac{B'}{B}=\dfrac{1}{4}\times\dfrac{r}{4r}=\dfrac{1}{16}$ and $B'=\dfrac{32}{16}=2\ \text{T}$.
Solution by Sreeraj P, M.Sc Physics