The magnetic field at the center of a circular orbit is given by B=2rμ0I.
The equivalent current due to the revolving electron is I=Te=2πrev.
Substituting I into the expression for B, we get B=4πr2μ0ev.
According to Bohr's model for a hydrogen atom, the velocity of the electron in the nth orbit is v∝n1 and the radius of the orbit is r∝n2.
Therefore, the magnetic field B depends on the principal quantum number n as B∝(n2)21/n⇒B∝n51.
The ratio of the magnetic fields in the 2nd and 4th orbits is B4B2=(n2n4)5=(24)5=25=32.
Answer: 32