In a photoelectric effect experiment, shining ultravioletlight on a metal surfac

Question

In a photoelectric effect experiment, shining ultravioletlight on a metal surface causes electrons to be ejected from thesurface at a speed of 2.62×105 m/s. Theejected electrons move toward an electrode located a few mm away.Applying a potential difference between the metal surface and theelectrode causes the electrons to speed up or slow down. Whatpotential difference will cause the electrons to come to rest justas they reach the electrode? Give your answer as a positive(changein V) if the electrode is at a higher potential than themetal surface, a negative (changeinV) if the electrode is at alower potential.

Explanation / Answer

Let the stopping potential Vo then    eV = ( 1/ 2) m v ^ 2      V = ( 1/ 2e ) m v ^ 2 where e =charge of electron = 1.6 * 10 ^ -19 C            m= mass of electron = 9.11 * 10 ^ -31 kg            v= Maximum speed = 2.62 * 10 ^ 5 m / s olug the values weget   V = [1/ ( 2* 1.6 * 10 ^ -19) ] [ 9.11* 10 ^ -31 *(2.62* 10 ^ 5 ) ^ 2 ]                                       = 19.54 * 10 ^ -2 Volt                                       = 0.1954 Volt

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