When the light of frequency 2$${\upsilon _0}$$ (where $${\upsilon _0}$$ is threshold frequency), is incident on a metal plate, the maximum velocity of electrons emitted is v₁ . When the frequency of the incident radiation is increased to 5$${\upsilon _0}$$ , the maximum velocity of electrons emitted from the same plate is v₂ . The ratio of v₁ to v₂ is

The de-Broglie wavelength of a neutron in thermal equilibrium with heavy water at a temperature T (kelvin) and mass m, is

Electrons of mass m with de-Broglie wavelength $$\lambda $$ fall on the target in an X-ray tube. The cutoff wavelength ($$\lambda $$₀) of the emitted X-ray is

Photons with energy 5 eV are incifent on a cathode C in a photoelectric cell. The maximum energy of emitted photoelectrons is 2 eV. When photons of energy 6 eV are incident on C, no photoelectrons will reach the anode A, if the stopping potential of A relative to C is