2) Two light sources are used in a photoelectric experimentto determine the work

Question

2) Two light sources are used in a photoelectric experimentto determine the work function for a particular metal surface. Whengreen light from a mercury lamp ( = 546.1 nm) isused, a stopping potential of 0.930 Vreduces the photocurrent to zero. (a) Based on this measurement, what is the workfunction for this metal?
eV
(b) What stopping potential would be observed when using light froma red lamp ( = 634.0nm)?
V (a) Based on this measurement, what is the workfunction for this metal?
eV
(b) What stopping potential would be observed when using light froma red lamp ( = 634.0nm)?
V V

Explanation / Answer

(a) by conservation of energy, wehave:    .         energy ofphoton = eV + workfunction       where V isstopping potential .         hc / =   0.930 eV    + workfunction .     4.14 x 10-15 * 3.00 x108 / 546.1 x 10-9   =  0.930 eV + work function .         2.274  =   0.930   + work function .     workfunction =   1.344 eV . (b) using the same formula... .           hc / =   e * stoppingpotential    + work function .     4.14 x 10-15 * 3.00 x108 / 634.0 x 10-9  =   e * stopping potential + 1.344 eV .       1.959 eV  =   e * stopping potential + 1.344 eV .         1.959 V = stopping potential + 1.344 V . stopping potential = 0.615 V

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