Correct option (a) 16.75 x 10-5 cm
Explanation:
If ne and n0 are refractive indices of extraordinary and ordinary rays in case of doubly refraction then thickness of wave plate are given as (ne - n0) = (in term of wavelength)
For half wavelength t1 = λ/2 ...(i)
For quarter wavelength t2 = λ/4 ...(ii)
By equation (i) and (ii) half wave plate = 2× thickness of quarter wave plate