NEET UG 2019 — Optics

Two similar thin equi-convex lenses of focal length $f$ each are kept coaxially in contact with each other, such that the focal length of the combination is ${F}_{1}.$ When the space between the two lenses is filled with glycerin (which has the same refractive index ($\mu =1.5$) as that of glass), then the equivalent focal length is ${F}_{2}.$ The ratio ${F}_{1}:{F}_{2}$ will be

Angular width of the central maxima in the Fraunhoffer diffraction for $\lambda=6000 Å$ is $\theta_0$. When the same slit is illuminated by another monochromatic light, the angular width decreases by $30 \%$. The wavelength of this light is

Pick the wrong answer in the context with rainbow.

In a Young's double slit experiment, if there is no initial phase-difference between the light from the two slits, a point on the screen corresponding to the fifth minimum has path difference.

In a double slit experiment, when light of wavelength $400 nm$ was used, the angular width of the first minima formed on a screen placed $1 m$ away was found to be $0.2^{\circ}.$ What will be the angular width of the first minima, if the entire experimental apparatus is immersed in water? $({\mu }_{water}=\frac{4}{3})$

An equi-convex lens has power $P$ it is cut into two symmetrical halves by a plane containing the principal axis. The power of one part will be

A double convex lens has focal length $25 \mathrm{~cm}$. The radius of curvature of one of the surfaces is doubled of the other. Find the radii, if the refractive index of the material of the lens is 1.5.

In total internal reflection, when the angle of incidence is equal to the critical angle for the pair of media in contact, what will be angle of refraction?