Glass has refractive index ' $n$ ' with respect to air and ' $\theta$ ' is the critical angle for a ray of light going from glass to air. If a ray of light is incident from air on the glass with angle of incidence ' $\theta$ ', corresponding angle of refraction is

A lens of power +5 D is put in contact with a lens of power -3 D . The combination will behave like a

A plane wavefront of width ' $x$ ' is incident on an air-water interface and the corresponding refracted wavefront has a width ' y ' as shown in figure. The refractive index of air with respect to water in terms of distances ' $w$ ' and ' $z$ ' is $(\mathrm{AD}=\mathrm{w}, \mathrm{CB}=\mathrm{z})$

The intermediate image formed by an objective lens of a compound microscope is