12/9/13, 9:15 PMPRE-LAB 14: Photoelectric Effect

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In procedure 1: suppose the maximum frequency light that hits the metal in the phototube has

frequency 5.92x1015 Hz. You find that a stopping potential of 5.92 V is required to stop thephotoelectrons.

a) Find the kinetic energy of these emitted electrons. .000000000000000000947 J

b) Find the work function for this metal. .000000000000000002978 J

c) Find the cut-off frequency for this metal. 4490000000000000 Hz

PRE-LAB 14: Photoelectric Effect (Homework)David KorffPhysics 122/146 FALL 2013, section Tue 6:55 PM, Fall 2013Instructor: Ilmo Sung

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12/9/13, 9:15 PMPRE-LAB 14: Photoelectric Effect

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a) Look at the photograph of the lab set-up. Since the light source gets very hot, what affect do theheated photons have on photoemission?

b) You use the same set-up to measure the stopping potential Vs through different filters. Suppose a

filter allowed through only light of frequency fo (the cut-off frequency) or lower. In this case, what would

the stopping potential be?

they increase the number of photoelectrons, but by the same amount no matter how hot thelight source

none, since infrared photons are below the cut-off frequency

none, since the infrared photons are absorbed by the air before they reach the metal

they increase the number of photoelectrons; the hotter the light source, the more effect theyhave

they decrease the number of photoelectrons by heating the metal and raising the work function

greater than zero: electrons escape, and must be stopped from drifting to the anode

zero

you need no stopping potential because no electrons escape from the metal

you cannot tell, since different electrons will escape with different speeds