Light is incident on a glass plate $(\mu = 1.5)$ such that the angle of refraction is $60^\circ$. $A$ dark band is observed corresponding to a wavelength of $6000 \, \mathring A$. If the thickness of the glass plate is $1.2 \times 10^{-3} \, mm$,find the order of the interference band.

In a biprism experiment, the distance of the source from the biprism is $1 \, m$ and the distance of the screen from the biprism is $4 \, m$. The refracting angle of the biprism is $\alpha = 2 \times 10^{-3} \, \text{radians}$. The refractive index $\mu$ of the biprism is $1.5$ and the wavelength of light used is $\lambda = 6000 \, \mathring{A}$. How many fringes will be seen on the screen?

In a biprism experiment,monochromatic light of wavelength $\lambda$ is used. The distance between two coherent sources is kept constant. If the distance between the slit and the eyepiece $(D)$ is varied as $D_{1}, D_{2}, D_{3}$ and $D_{4}$,and the corresponding measured fringe widths are $z_{1}, z_{2}, z_{3}$ and $z_{4}$,then:

Assertion: At the first glance,the top surface of the Morpho butterfly's wing appears a beautiful blue-green. If the wind moves the colour changes.
Reason: Different pigments in the wing reflect light at different angles.

The thickness of a plate having refractive index $\mu$ which will produce a change in optical path equal to half the wavelength $\lambda$ of the light passing through it is

In a Fresnel's biprism experiment,a mica sheet of refractive index $1.5$ and thickness $6 \times 10^{-6} \ m$ is placed in the path of one of the interfering beams. As a result,the central fringe shifts by a distance equal to $5$ fringe widths. The wavelength of light used is .... $\mathring{A}$