Question

An electron makes a transition from $n=2$ to $n=1$ state in a hydrogen like atom.

• A. magnetic field at the site of nucleus is decreased by 16 times.
• B. magnetic field at the site of nucleus is increased by 32 times
• C. angular momentum of electron is changed
• D. none of these

Answer 1

Answer: (B), (C)

The correct options are
B magnetic field at the site of nucleus is increased by 32 times
C angular momentum of electron is changed

Magnetic field at centre (site of nucleus):
$B=\frac{{\mu }_{0}I}{2r}=\frac{{\mu }_{0}qf}{2r}=\frac{{\mu }_{0}qv}{2r\times 2\pi r}\Rightarrow B\alpha \frac{1}{r^2}$ and $B\propto v$
$\therefore B\propto \frac{1}{n^5}$
$\frac{B_1}{B_2}=\frac{(2{)}^5}{(1{)}^5}$
(since, $n_1=1$ to $n_2=2)$
$\therefore B_1=32B_2$
Also, $mvr=n.\frac{h}{2\pi },$therefore angular momentum is changed by $\frac{h}{2\pi }$.