JEE Main 2017 · 8 Apr · Shift 1 · Physics Q25

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According to Bohr's theory, the time averaged magnetic field at the centre (i.e. nucleus) of a hydrogen atom due to the motion of electrons in the n $^{\text{th}}$ orbit is proportional to : (n = principal quantum number)

n^{-4}

n^{-5}

n^{-3}

n^{-2}

Answer and worked solution

Official answer: B

The current is $I=\dfrac{ev}{2\pi r}$ and the field $B=\dfrac{\mu_0I}{2r}\propto\dfrac v{r^2}$ . In Bohr's model $v\propto\frac1n$ and $r\propto n^2$ , so $B\propto n^{-5}$ .

Topics:Bohr model and hydrogen spectrum Biot-Savart law

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JEE Main 2017 · 8 Apr · Shift 1, Physics question 25