Wave Optics

Q: A parallel beam of light strikes a piece of transparent glass having cross section as shown in the figure below . Correct shape of the emergent wavefront will be

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Ans: (a)

Sol:

Q: A man wants to distinguish between two pillars located at a distance of 11 km. What should be the minimum distance between the pillars ?

Sol: As the limit of resolution of human eye is

$\displaystyle \theta = 1′ = (\frac{1}{60})^o $

$\displaystyle \theta = \frac{\pi}{60 \times 180} $

If x is minimum distance between the pillars,

and d = 11 km = 11 × 10³ m ,

then from $\displaystyle \theta = \frac{x}{d} $

$\displaystyle x = d \times \theta $

$\displaystyle x = 11 \times 10^3 \times \frac{\pi}{60 \times 180} $

x = 3.2 m

Q: Two beams, A and B of plane polarized light with mutually perpendicular planes of polarization are seen through a polaroid. From the position when the beam A has maximum intensity. (and beam B has zero intensity), a rotation of polaroid through 30° makes the two beams appear equally bright. If the initial intensities of the two beams are I_A and I_B respectively, then I_A/I_B equals.

(a) 1

(b) 1/3

(c) 3

(d) 3/2

Q: A beam of light λ = 600 nm from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2 m away. The distance between first dark fringes on either side of the central bright fringe is

(a) 1.2 cm

(b) 1.2 mm

(c) 2.4 cm

(d) 2.4 mm