CBSE Class 12 Physics 2017 Delhi Set 3 Paper

Question : 4

Total: 8

SECTION -C

(i) State two important features of Einstein's photoelectric equation.
(ii) Radiation of frequency 1015‌Hz is incident on two photosensitive surfaces P and Q. There is no photoemission from surface P. Photoemission occurs from surface Q but photoelectrons have zero kinetic energy. Explain these observations and find the value of work function for surface.

Solution:

(i) Two important features of Einstein's photo electric equation
(ii) Explanation of observations and finding value of work function of surface Q
(i) Maximum kinetic energy (Kmax), of emitted electrons, depends linearly on frequency of incident radiations
K‌max ‌=hv−hv0
Existence of threshold frequency for the metal surface ϕ0=hv0
(Any other relevant feature)
(ii) Since no photoelectric emission takes place from P it means frequency of incident radiation (1015‌Hz) is less than its threshold frequency (v0)p.
Photo emission takes place from Q but kinetic energy of photoelectrons is zero. This implies that frequency of incident radiation is just equal to the threshold frequency of Q.
For Q,
work function
ϕ0‌=hv0
‌=‌

6.6×10−34×1015

1.6×10

‌eV
‌=4.125‌eV

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