The Total solution for NCERT class 6-12
Ultraviolet light of wavelength 2271 Å froma 100 W mercury source irradiates a photo-cell made of molybdenum metal. If thestopping potential is −1.3 V, estimate the work function of the metal. Howwould the photo-cell respond to a high intensity (∼105 W m−2) redlight of wavelength 6328 Å produced by a He-Ne laser?
Wavelength of ultraviolet light, λ =2271 Å = 2271 × 10−10 m
Stopping potential of the metal, V0 =1.3 V
Planck’s constant, h = 6.6× 10−34 J
Charge on an electron, e =1.6 × 10−19 C
Frequency of light = ν
We have the photo-energyrelation from the photoelectric effect as:
= hν − eV0
Let ν0 be thethreshold frequency of the metal.
∴= hν0
Wavelength of red light, = 6328 × 10−10 m
Since ν0> νr,the photocell will not respond to the red light produced by the laser.