Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be 3.57 V. The threshold frequency of the material is

A 200 W sodium street lamp emits yellow light of wavelength 0.6 $$\mu $$m. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is

The threshold frequency for a photosensitive metal is 3.3 $$ \times $$ 10¹⁴ Hz. If light of frequency 8.2 $$ \times $$ 10¹⁴ Hz is incident on this metal, the cut- off voltage for the photoelectron emission is nearly

Light of two different frequencies whose photons have energies 1 eV and 2.5 eV respectively illuminate a metallic surface whose work function is 0.5 eV successively. Ratio of maximum speeds of emitted electrons will be