Electro Magnetic radiation having wavelength of 310 angstrom are subjected to a metal sheet having work function (phi) of 18.8 ev(electron volt) . What will be the velocity of photo electron with maximum Kinetic energy?
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Answer:
K. Ehf - O
h = planks constant = 6.62 × 10-34
f = c/y
c = speed of light in air = 3.0 × 108 m/s
y=3.10\times10^{-9}m
\phi=12.8\times1.6\times10^{-19}=2.016\times10^{-18} Joules.
f = (3 × 10³) / (3.10 × 10-9) 9.6774 × 10¹6
X
hf=9.6774\times10^{16}\times6.62\times10^{-34}=6.41\times10^{-17}
=
Joules
K. E = 6.41 × 10-17 - 2.016 × 10-18 = 6.2084 ×
10-¹7 joules.
K. E = 1/2mv²
m = mass of an electron = 9.1 x 10-³1
6.2084\times10^{-17}=0.5\times9.1\times10^{-31}v^{2}
V^{2}=1.3645\times10^{14}
V=1.1681\times10^{7}m/s