THE PHOTOELECTRIC EFFECT

EMR

Heinrich Hertz (1887)

When Hertz was testing Maxwell’s theory of electromagnetic waves he discovered that ultraviolet light caused some metallic surfaces to lose their negative charge.

Explanation: When EMR strikes a metal surface, electrons are released from the plate.

PhotoElectric Effect

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

Experimental Results

Photoelectrons are only emitted if the incident light is above a certain frequency, known as the threshold frequency (fo).

Different materials have different threshold frequencies.

The release of electrons only occurs if a single photon hitting the metal target transfers its energy to one electron, giving that one electron the energy to move. The photon must have some minimum amount of energy to snap the electron off the metal.

3e

The release of electrons only occurs if

of f

Increased frequency or decreased wavelength or increased energy of a photon results in increased Ek of the emitted photoelectron.

Eg. 2 Determine the work function of a metal in Joules if the maximum threshold wavelength is 1.25 x 10-7 m.

34 8

7

18

6.63 10 *(3.00 10 / )

1.25 10

1.59 10

o

E hf

hcE

hc Js m sW

m

J

Some Light Listening

http://www.youtube.com/watch?v=bjOGNVH3D4Y&feature=related

http://www.youtube.com/watch?v=FBJNBdo2Cps&feature=related