$A$ bulb emits monochromatic yellow light of the wavelength $0.57 \ \mu m$. If the rate of emission of quanta per second of the bulb is $14.33 \times 10^{19}$, the power of the bulb (in $Watt$) is $.....$

$A$ source of monochromatic radiation of wavelength $400 \, nm$ provides $1000 \, J$ of energy in $10 \, seconds$. When this radiation falls on the surface of sodium,$x \times 10^{20}$ electrons are ejected per second. Assume that wavelength $400 \, nm$ is sufficient for ejection of electrons from the surface of sodium metal. The value of $x$ is $......$. (Nearest integer) $(h = 6.626 \times 10^{-34} \, Js)$

If the electron of a hydrogen atom is present in the first orbit,the total energy of the electron is

The wavelength of the first line of the Balmer series is $656 \ nm$. Calculate the wavelength of the second line of this series. (Note: First line means $n=3 \to n=2$ and second line means $n=4 \to n=2$)

In the hydrogen spectrum,if an electron transitions from the $6^{th}$ orbit to the $3^{rd}$ orbit,what is the total number of spectral lines in the visible region?

The work function $(W_0)$ of $Li, K, Mg, Ag$ and $Cu$ are $2.42, 2.25, 3.70, 4.30$ and $4.80 \ eV$ respectively. The number of metals which undergo photoelectric effect if a radiation of wavelength $540 \ nm$ falls on them is $(1 \ eV = 1.602 \times 10^{-19} \ J)$.