# A mercury lamp is a convenient source for studying frequency dependence of photoelectric emission since it gives a number of spectral lines ranging from the UV to the red end of the visible spectrum. In our experiment with rubidium photo-cell, the following lines from a mercury source were used:λ1 = 3650 Å, λ2 = 4047 Å, λ3 = 4358 Å, λ4 = 5461 Å, λ5 = 6907 Å,The stopping voltages, respectively, were measured to be:V01 = 1.28 V, V02 = 0.95 V, V03 = 0.74 V, V04 = 0.16 V, V05 = 0 VDetermine the value of Planck’s constant h, the threshold frequency and work function for the material.[Note: You will notice that to get h from the data, you will need to know e (which you can take to be 1.6 × 10–19 C). Experiments of this kind on Na, Li, K, etc. were performed by Millikan, who, using his own value of e (from the oil-drop experiment) confirmed Einstein’s photoelectric equation and at the same time gave an independent estimate of the value of h.]

Given: The frequency, v of a wave with wavelength λ is given by,

v = c/λ …(1)

(c = speed of light = 3 × 108ms-1)

By using equation (1) we can find frequency for each case, The equation for photo-electric effect is given as,

Φ0 = hv- eV0

We can rewrite this equation as,

V0 = …(2)

Where,

h = Planck’s constant

c = speed of light = 3 × 108m

λ = wavelength of light

e = charge on each electron = 1.6 × 10-19C We find that the slope of the graph remains same,

Slope of the line = From equation (2),

We can write,

Slope = h/e

h = e × slope

h = h = 6.58 × 10-34 Js

From the same graph, we can infer that, threshold frequency of the metal is 5 × 1014 Hz

i.e. v0 = 5 × 1014Hz

Work function, Φ0 = hv0 …(2)

Where,

h = Plank’s constant = 6.57 × 10-34Js

v0 = threshold frequency

By plugging the data in equation (2), we get,

Φ0 = 6.57 × 10-34Js × 5 × 1014Hz

Φ0 = 3.28 × 10-19 J Φ0 = 2eV

Hence, the work function of the metal is 2eV.

Rate this question :

How useful is this solution?
We strive to provide quality solutions. Please rate us to serve you better.
Related Videos  Photoelectric Effect | World of Photons45 mins  Pedigree chart58 mins  Medelian disorder series: Thalassemia, Sickle cell anaemia & Phenylketonuria60 mins  Everything About Genetic DisordersFREE Class  Human Evolution | An Important Concept40 mins  How to solve applied questions based on Mendel's law of inheritance46 mins  Interactive Quiz on Principles of Inheritance and Variation33 mins  How to solve questions of pedigree chart49 mins  Rotational Kinetic Energy43 mins  Interactive Quiz | Questions based on torque & angular momentum44 mins
Try our Mini CourseMaster Important Topics in 7 DaysLearn from IITians, NITians, Doctors & Academic Experts
Dedicated counsellor for each student
24X7 Doubt Resolution
Daily Report Card
Detailed Performance Evaluation view all courses 