Page 262 - Essentials of physical chemistry

224 Essentials of Physical Chemistry

Stopping potential for Na
1.4
Stopping potential (eV) 1.2 1 y = 0.4134x – 2.3591

0.8
2
R =1
0.6
0.4
0.2
0
0 1 2 3 4 5 6 7 8 9
14
Frequency (10 Hz)
FIGURE 10.9 The stopping potential for photoelectrons from sodium versus frequency of the exciting light
(photons). The modern value of the work function of sodium is 2.36 eV. (From Lide, D.R. Ed., CRC Handbook
of Chemistry and Physics, 90th Edn., CRC Press, Boca Raton, FL, 2009–2010, pp. 12–121.)

TABLE 10.1
Work Function for Selected Metals
versus Photoelectric n 0 Values

Element W f (eV) l 0 (Å) n 0 (10 14 Hz)
Cs 1.95 6358.15 4.715087
K 2.29 5414.15 5.537204
Na 2.36 5253.56 5.706464
Li 2.93 4231.54 7.084720
Mg 3.66 3387.54 8.849855
Be 4.98 2489.64 12.041606

W f vs. stopping frequency
6 5
Stopping potential (eV) 4 3 y = 0.4136x –3E-08
2
R =1

1 2
0
0 2 4 6 8 10 12 14
14
Stopping frequency (10 Hz)
FIGURE 10.10 Work function versus stopping frequency for selected Group I and II metals.