CK-12-Physics - Intermediate

http://www.ck12.org Chapter 23. Quantum Physics

Vo→−Vo

SoKEmax=eVo,

WhereVois called the stopping potential or stopping voltage.

Follow the links below for more information on the photoelectric effect.

http://www.youtube.com/watch?v=X6WNLqFWMN8

http://www.youtube.com/watch?v=N7BywkIretM

Table23.1 summarizes some of the differences between the predictions of Maxwell’s classical electromagnetic

theory and of Einstein’s modern physics theory for the photoelectric effect.

TABLE23.1:

Increasing Intensity Increasing Frequency

Classical (Maxwell) More electrons ejected with greater

kinetic energy

No effect

Modern (Einstein) More electrons ejected with same

kinetic energy

Greater kinetic energy of ejected

electrons (Minimum frequency re-

quired to eject any electrons)KE=

h f−Wo

Note that the relationship between the maximum kinetic energyKEmaxof the ejected electrons and the frequency of

lightfincident on the material is linear as shown inFigure23.7.

FIGURE 23.7

TheTable23.2 gives the work functions(Wo)for some common materials.

TABLE23.2:

Element Average Work Function(eV)Wo=h fo

Aluminum 4.16

Calcium 2.87

Copper 4.82

Lead 4.25

Nickel 5.20

Potassium 2.29

Silicon 4.73

Silver 4.63

Sodium 2.36

Uranium 3.77