Questions on the Photoelectric Effect
Q7.
The stopping potential VS for a photoelectric cell is measured for light of two frequencies. The following results are obtained:
stopping potential VS/V |
0.93 |
1.41 |
frequency/1014 Hz |
6.10 |
7.30 |
Use this data to determine a value for the Planck constant.
For photoelectrons:
EK = eVS
Now
hf = φ + EK(MAX)
so
hf = φ + eVS
and
φ = hf - eVS
hf1 - eVS1 = hf2 - eVS2
h (f1 - f2) = e (VS1- VS2)
h (7.30 - 6.10) x 1014= e (1.41 - 0.93)
h = 1.60 x 10-19 x 0.48 /(1.20 x 1014)
h = 6.40 x 10-34 Js
(Total 4 marks)