1.

A light beam of wavelength 6400 Å is incident normally on the surface of a glass slab of thickness 5 cm. Its wavelength in glass is 4000 A. The beam of light takes the same time to travel from the source to the surface as it takes to travel through the glass slab. Calculate the distance of the source from the surface.

Answer»

Data : λa = 6400 Å, 

sg = thickness of the glass slab = 5 cm, 

λg = 4000 Å

The speeds of light in glass and air are, respectively, vg = λgv and va = λav where the frequency of the light v remains unchanged with the change of medium. 

The time taken to travel through the glass slab,

tg\(\cfrac{S_g}{v_g}\) = \(\cfrac{S_g}{λ_gv}\)

The time taken to travel through air,

 ta\(\cfrac{S_a}{v_a}\) = \(\cfrac{d}{λ_av}\)

where sa = d is the distance of the glass surface from the source.

Since ta = tg

\(\cfrac{d}{λ_av}\) = \(\cfrac{S_g}{λ_gv}\)

∴ d = \(\cfrac{λ_a}{λ_g}\) SgSg = \(\frac{6400}{4000}\) x 5 = 1.6 × 5 = 8 cm



Discussion

No Comment Found

Related InterviewSolutions