A small object is placed in front of convex lens of focal length $\frac{25}{4} \mathrm{cm}$, such that a virtual image is formed at a distance of $25 \mathrm{cm}$. The magnification produced is 
(Choose From: $6.25, 5, 2.25$)

A student traces the path of a ray of light passing through a rectangular glass slab for three different values of angle of incidence $(\angle i)$ namely $30°, 45°, \mathrm{and} 60°$. He extends the direction of incident ray by a dotted line and measures the perpendicular distance 'l' between the extended incident ray and the emergent ray. He will observe that:

The refractive index of glass is $1.5$. The critical angle of the glass is,