When a hydrogen atom emits a photon during a transition from $n=4$ to $n=2$,its recoil speed is about (in $m \ s^{-1}$)

What is an emission line?

$A$ photon of wavelength $\lambda$ is absorbed by an electron confined to a box of length $L = \sqrt{(35 h \lambda / 8 m c)}$. As a result,the electron makes a transition from state $k=1$ to the state $n$. Subsequently,the electron transitions from the state $n$ to the state $m$ by emitting a photon of wavelength $\lambda^{\prime} = 1.75 \lambda$. Then,

In the hydrogen atom,if the reference level of potential energy is assumed to be zero at the ground state level,choose the incorrect statement.

The $1^{st}, 2^{nd},$ and $3^{rd}$ energy levels of an atom are $E, 4E/3,$ and $2E$ respectively. If a wavelength $\lambda$ is emitted during the transition $3 \to 1$,what is the wavelength emitted during the transition $2 \to 1$?

The following diagram indicates the energy levels of a certain atom. When the system moves from the $2E$ level to the $E$ level,a photon of wavelength $\lambda$ is emitted. The wavelength of the photon produced during its transition from the $\frac{4E}{3}$ level to the $E$ level is