JEE Main 2026 · 2 Apr · Shift 2 · Physics Q47

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PhysicsInteger+4 / -1Question 47 of 75

Using Bohr's model, calculate the ratio of the magnetic fields generated due to the motion of the electrons in the 2nd and 4th orbits of hydrogen atom ________.

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Answer and worked solution

Official answer: 32

Field at the nucleus. $B=\dfrac{\mu_0I}{2r}$ with $I=\dfrac{ev}{2\pi r}$ , so $B\propto\dfrac v{r^2}$ .

Bohr scaling. $v\propto\frac1n$ and $r\propto n^2$ , so $B\propto n^{-5}$ .

Ratio. $\dfrac{B_2}{B_4}=\left(\dfrac42\right)^5=32$ .

Answer: 32

Topics:Bohr model and hydrogen spectrum Biot-Savart law

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JEE Main 2026 · 2 Apr · Shift 2, Physics question 47