If a photon has velocity $c$ and frequency $\nu$, then which of following represents its wavelength

When monochromatic radiation of intensity $I$ falls on a metal surface, the number of photoelectrons and their maximum kinetic energy are $N$ and $K$ respectively. If the intensity of radiation is $2I$, the number of emitted electrons and their maximum kinetic energy are respectively

A photon of $1.7 \times {10^{ – 13}}$ Joules is absorbed by a material under special circumstances. The correct statement is

Find the number of photons emitted per second by a $25$ watt source of monochromatic light of wavelength $6600 \mathring A$. What is the photoelectric current assuming $3 \%$ efficiency for photoelectric effect?

An important spectral emission line has a wavelength of $21 cm$. The corresponding photon energy is

$(h = 6.62 \times {10^{ – 34}}Js;\;\;c = 3 \times {10^8}m/s)$