Dual Nature Of Light Question 118
Question: In a photocell bichromatic light of wavelength 2475 Å and 6000 Å are incident on cathode whose work function is 4.8 eV. If a uniform magnetic field of 3 ´ 10?5 Tesla exists parallel to the plate, the radius of the path describe by the photoelectron will be (mass of electron = 9 ´ 10?31 kg)
Options:
A) 1 cm
B) 5 cm
C) 10 cm
D) 25 cm
Show Answer
Answer:
Correct Answer: B
Solution:
Energy of photons corresponding to light of wave length l1 = 2475 Å is $ E_{1}=\frac{12375}{2475}=5,eV. $ and that corresponding to l2 = 6000 Å is $ E_{2}=\frac{12375}{6000}=2.06,eV $ As E2 < W0 and E1 > W0 Photoelectric emission is possible with l1 only. Maximum kinetic energy of emitted photoelectrons K = E ? W0 = 5 ? 4.8 = 0.2 eV. Photo electrons experiences magnetic force and move along a circular path of radius $ r=\frac{\sqrt{2,mk}}{Q,B}=\frac{\sqrt{2\times 9\times {{10}^{-31}}\times 0.2\times 1.6\times {{10}^{-19}}}}{1.6\times {{10}^{-19}}\times 3\times {{10}^{-5}}} $ = 0.05 m = 5 cm.
BETA
