The work function for the following metals is given: `Na: 2.75 eV, K: 2.30 eV, Mo: 4.17 eV, Ni: 5.15 ev`. Which of these metals will not give photoelectric emission for a radiation of wavelength `3300 Å` from a He-Cd laser placed 1 m away from the photocell? What happens if the laser is brought nearer and placed 50 cm away ?

Explanation

It is found that the given incident frequency ν is greater than `ν_(0) (Na), and ν_(0) (K)`, but less than `ν_(0) (Mo), and ν_(0) (Ni)`. Therefore, Mo and Ni will not give photoelectric emission. If the laser is brought closer, intensity of radiation increases, but this does not affect the result regarding Mo and Ni. However, photoelectric current from Na and K will increase in proportion to intensity.