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Einstein's photoelectric equation (intermediate)

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A monochromatic light source shines on a metallic surface A having work function ϕ0A=7 eV. The stopping potential is observed to be 4 V.
Find the stopping potential when the light source is used on another metal B having work function ϕ0B=5 eV.
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3/5
  • a simplified improper fraction, like 7/4
  • a mixed number, like 1 3/4
  • an exact decimal, like 0.75
  • a multiple of pi, like 12 pi or 2/3 pi