When an electron revolves in a stationary orbit,then:

$A$ $200 \ W$ bulb emits monochromatic light of wavelength $200 \ nm$. Calculate the number of photons emitted per second by the bulb.

Consider an electron moving in the first Bohr orbit of a $He^{+}$ ion with a velocity $v_1$. If it is allowed to move in the third Bohr orbit with a velocity $v_3$, then indicate the correct $v_3: v_1$ ratio.

The energy required to excite an electron in a hydrogen atom from the ground state $(n=1)$ to the first excited state $(n=2)$ is $..........$ $eV$.

Time taken for an electron to complete one revolution in the Bohr orbit of hydrogen atom is

If in a hydrogen atom,an electron jumps from the $3^{rd}$ Lyman line to the $1^{st}$ Lyman line,then the obtained wavelength is: