Optics Question 178
Question: A laser beam can be focussed on an area equal to the square of its wavelength A He-Ne laser radiates energy at the rate of 1mW and its wavelength is 632.8 nm. The intensity of focussed beam will be
Options:
A) $ 1.5\times 10^{13}W/m^{2} $
B) $ 2.5\times 10^{9}W/m^{2} $
C) $ 3.5\times 10^{17}W/m^{2} $
D) None of these
Show Answer
Answer:
Correct Answer: B
Solution:
Area through which the energy of beam passes $ =(6.328\times {{10}^{-7}})=4\times {{10}^{-13}}m^{2} $ \ $ I=\frac{P}{A}=\frac{{{10}^{-3}}}{4\times {{10}^{-13}}}=2.5\times 10^{9}W/m^{2} $
