One day on a spacecraft corresponds to $2$ days on the earth. The speed of the spacecraft relative to the earth is
$1.5 \times {10^8}m{s^{ - 1}}$
$2.1 \times {10^8}m{s^{ - 1}}$
$2.6 \times {10^8}m{s^{ - 1}}$
$5.2 \times {10^8}m{s^{ - 1}}$
In a dark room of photography, generally red light is used. The reason is
If a photon has velocity $c$ and frequency $\nu$, then which of following represents its wavelength
The minimum intensity of light to be detected by human eye is ${10^{ - 10}}W/{m^2}$. The number of photons of wavelength $5.6 \times {10^{ - 7}}m$ entering the eye, with pupil area ${10^{ - 6}}{m^2}$, per second for vision will be nearly
An electron and proton are separated by a large distance. The electron starts approaching the proton with energy $3\, {eV}$. The proton captures the electrons and forms a hydrogen atom in second excited state. The resulting photon is incident on a photosensitive metal of threshold wavelength $4000\, \mathring {{A}}$. What is the maximum kinetic energy of the emitted photoelectron ? (In ${eV}$)
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?