3. Photoelectric effect.

Question 1

What is the photoelectric effect?

Give its formula.

It depends on… ?

Answer 1

Photoelectrons emitted from matter as a consequence of the absorption of E from EM radiation of very short wavelength and high E

E_kin = h*f - W_ex

• Increasing J only changes number of e^-_emitted (changes photoelectric current)
• v depends on wavelength & frequency (color)
• specific threshold level for each metal
• Appears instantaneously upon radiation

Question 2

What are the properties of a photoelectron?

Answer 2

• travels with c in vacuum
• doesn’t exist in rest
• no rest mass

Question 3

Explain the significance of the photoelectric effect. Refer to the scintillation counter and give 2 other applications.

Answer 3

Scintillator counter:

Incoming radiation is transformed into a photoelectron. This photoelectron is multiplied in the PMT.

Other applications of the photoelectric effect:

• Solar cells: light energy (photons) are transformed into electrons and an electric current.
• Photoelectric cell: detects light by measuring transforming photons into electric current and measure it.

Question 4

Explain the experiment where we could observe photoelectric effect and tell who discovered it.