Monochromatic light of photon energy ejects photo-electrons from an unknown metal surface

PHYSICS · Multi-part · A Level · Physics · Particles and radiation · Particles and radiation

Problem

Monochromatic light of photon energy 4.50 eV4.50\,\text{eV} ejects photo-electrons from an unknown metal surface, and the stopping potential measured is 0.80 V0.80\,\text{V}. Assume h=6.63×10−34 J sh = 6.63\times10^{-34}\,\text{J\,s}, c=3.0×108 m s−1c = 3.0\times10^{8}\,\text{m\,s}^{-1} and e=1.6×10−19 Ce = 1.6\times10^{-19}\,\text{C}. (i) Determine the work function and the threshold wavelength of the metal. (ii) Keeping the intensity of illumination unchanged, the photon energy is increased by 20 %20\,\%. Calculate the new maximum kinetic energy of the emitted electrons and the corresponding stopping potential. (iii) By what percentage does the speed of the fastest electrons increase due to the change in photon energy? (Assume non-relativistic speeds.)

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