Incident light
This presentation is the property of its rightful owner.
Sponsored Links
1 / 9

Photoelectric Equation: PowerPoint PPT Presentation


  • 54 Views
  • Uploaded on
  • Presentation posted in: General

Incident light. Cathode. Anode. A. V. +. -. Stopping potential:. V o = 0.800 V. Example 4: The threshold frequency for a given surface is 1.09 x 10 15 Hz . What is the stopping potential for incident light whose photon energy is 8.48 x 10 -19 J ? . Photoelectric Equation:.

Download Presentation

Photoelectric Equation:

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Photoelectric equation

Incident light

Cathode

Anode

A

V

+

-

Stopping potential:

Vo= 0.800 V

Example 4:The threshold frequency for a given surface is 1.09 x 1015 Hz. What is the stopping potential for incident light whose photon energy is 8.48 x 10-19 J?

Photoelectric Equation:

W = (6.63 x 10-34 Js)(1.09 x 1015 Hz) =7.20 x 10-19 J


Total relativistic energy

Total Energy, E

Total Relativistic Energy

Recall that the formula for the relativistic total energy was given by:

For a particle with zero momentum p= 0:

E =moc2

A light photon has mo= 0, but it does have momentum p:

E =pc


Waves and particles

Wavelength of a photon:

de Broglie Wavelength:

Waves and Particles

We know that light behaves as both a wave and a particle. The rest mass of a photon is zero, and its wavelength can be found from momentum.

All objects, not just EM waves, have wavelengths which can be found from their momentum


Finding momentum from k e

Momentum from K:

Finding Momentum from K.E.

In working with particles of momentum p = mv, it is often necessary to find the momentum from the given kinetic energy K. Recall the formulas:

K = ½mv2 ; p = mv

Multiply first Equation by m:

mK =½m2v2= ½p2


Example 5 what is the de broglie wavelength of a 90 ev electron m e 9 1 x 10 31 kg

-

e-

90 eV

Example 5:What is the de Broglie wavelength of a 90-eV electron? (me = 9.1 x 10-31 kg.)

Next, we find momentum from the kinetic energy:

p = 5.12x 10-24 kg m/s

l = 0.122 nm


Summary

Planck’s Equation:

E = hf (h = 6.626 x 10-34 J s)

Photon

1 eV = 1.60 x 10-19 J

The Electron-volt:

E = hf

1 MeV = 1.6 x 10-13 J

1 keV = 1.6 x 10-16 J

Summary

Apparently, light consists of tiny bundles of energy called photons, each having a well-defined quantum of energy.


Summary cont

Incident light

Cathode

Anode

A

C

Ammeter

Threshold wavelength lo

A

+

-

Summary (Cont.)

If lis innm, the energy ineV is found from:

Wavelength in nm; Energy in eV


Summary cont1

Stopping potential

V

Slope

y

fo

x

Frequency

Summary (Cont.)

Planck’s Experiment:

Incident light

Cathode

Anode

V

A

+

-

Potentiometer

Kmax = eVo


Summary cont2

Wavelength of a photon:

de Broglie Wavelength:

Summary (Cont.)

Quantum physics works for waves or particles:

For a particle with zero momentump = 0:

E =moc2

A light photon has mo = 0, but it does have momentum p:

E =pc


  • Login