A monochromatic beam of light of wavelength $400\,nm$ incident normally upon a photosensitive surface ($25\%$ reflects and rest absorbs), produces a pressure of $5 \times 10^{-7}\,Nm^{-2}$ on it. If $0.1\%$ of the incident photons produce electrons then corresponding saturation current will be…………..$\mu A$ (consider area of photosensitive surface $= 5\,cm^2$)

A point source of light is used in an experiment on photoelectric effect. Which of the following curves best represents the variation of photo current $(i)$ with distance $(d)$ of the source from the emitter

An astronaut floating freely in space decides to use his flash light as a rocket. He shines a $10$ watt light beam in a fixed direction so that he acquires momentum in the opposite direction. If his mass is $80$ kg, how long must he need to reach a velocity of $1$ $ms^{-1}$

A small object at rest, absorbs a light pulse of power $20\,mW$ and duration $300\,ns$. Assuming speed of light as $3 \times 10^8\,m / s$. the momentum of the object becomes equal to $………\times 10^{-17} kg\,m / s$

There are materials which absorb photons of shorter wavelength and emit photons of longer wavelength. Can there be stable substances which absorb photons of larger wavelength and emit light of shorter wavelength.