# If in a circular coil $A$ of radius $R$, current $I$ is flowing and in another coil $B$ of radius $2R$ a current $2I$ is flowing, then the ratio of the magnetic fields, $B_{A}$ and $B_{B}$ , produced by them will be Option 1) 1 Option 2) 2 Option 3) 1/2 Option 4) 4

S Sabhrant Ambastha

As we learnt in concept

Magnetic Field due to circular coil at Centre -

$B_{Centre}=\frac{\mu_{0}}{4\pi }\frac{2\pi Ni}{r}=\frac{\mu_{0} Ni}{2r}$

$\therefore \; \; \frac{B_{A}}{B_{B}}=\frac{I_{A}}{I_{B}}\times \frac{R_{B}}{R_{A}}=\left ( \frac{1}{2} \right )\left ( \frac{2}{1} \right )=1$

Option 1)

1

Correct option

Option 2)

2

Incorrect option

Option 3)

1/2

Incorrect option

Option 4)

4

Incorrect option

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