Double slit interference The separation distance between sli

Double slit interference: The separation distance between slits is known to be 381 um. A screen is 3m away using a an HeNe laser (635nm). What is the light intensity of the second and third maximum?

Solution

for second maxima:

for second maxima:

dsin@ = m*lambda

       dsin@ /lambda = m

                               = 1

the intensity for the second maxima is,

   I₂ = I_o [cos²{pi*dsin@ /lambda}] = I_o [cos²{pi}] = I_o

for third maxima:

dsin@ = m*lambda

       dsin@ /lambda = m

                               = 2

the intensity for the third maxima is,

   I₃ = I_o [cos²{pi*dsin@ /lambda}] = I_o [cos²{2*pi}] = I_o