QUANTUM THEORY

 

 

E = h. f

 

E:  Energy of single quantum

f:  Frequency of vibrating molecule or atom (Hz or 1/s)

h:  Blanck’s Constant:  6.63 x 10-34 J.s

 

E = n. h. f

n:  Energy of quanta (whole number 1, 2, 3, 4……)

 

 

c = f. λ

λ:  Wavelength of light (m)

c:  Speed of light (3.00 x 108 m/s)

 

 

Threshold frequency:  Minimum frequency at which photoelectrons are liberated from a given photoelectric surface

 

 

Ephoton = W + Ek

 

Ek =  Ephoton - W

 

Ek =  h. f - W

 

 

1eV:  1.60 x 10-19 J

 

Ek = e. V0

 

Ek:  Kinetic energy of photoelectron (J)

 

V0:  Retarding potential (V):  Smallest potential difference to reduce to photocurrent to zero.

 

e:  Charge of single electron (1.602 x 10-19C)

 

Ephoton:  Energy of incident photon (J)

 

W:  Work function:  Energy needed to release an electron from an illuminated metal.   It is different for different metal.  Energy with which the electron is bound to the photoelectric surface (J)

 

Momentum of Photon:

 

Pphoton = P’photon + P’electron

 

 

Compton Relationship:

 

P:  Momentum of a photon (kg.m/s)

h:  Blanck’s Constant:  6.63 x 10-34 J.s

λ:  Wavelength (m)

 

 

λ:  Broglie Wavelength:  Wavelength associated with the motion of a particle possessing momentum (m)

 

v:  Speed of the object (m/s)

m:  Mass of the object (kg)