COMEDK Exam 2022 Solved Paper

Given, power of laser beam,
P=30mW=30×10−3W
Area of cross section, A=15mm2=15×10−6m2
Permittivity of free space, ε0=9×10−12 SI unit
Speed of light, c=3×108m∕s
Intensity of electromagnetic wave is given by
I=

1

2

ncε0E2
where, n is refravctive index for air, n=1
I=

1

2

c.ε0E2 ............(i)
I=

P

A

...............(ii)
From Eqs. (i) and (ii), we get

1

2

cε0E2=

P

A

E2=

2P

Acε0

E=√

2×30×10−3

15×10−6×3×108×9×10−12

=1.22×103V∕m=1.22kV∕m