Why does the light ray incident in a rectangular glass slab emerge parallel to incident ray ?

Draw a ray diagram to show the formation of an image when an object is placed between $\mathrm{F}$ and $\mathrm{P}$ of a concave mirror.

A needle placed $45 \mathrm{cm}$ from a convex lens, forms an image on a screen placed $90 \mathrm{cm}$ on the other side of a lens. Determine its focal length. What is the size of the image if the object is $5 \mathrm{cm}$ ?

Draw a ray diagram to show the formation of an image when an object is placed between focus $\left({\mathrm{F}}_1\right)$ and optical centre $\left(\mathrm{O}\right)$ of a convex lens.

A concave mirror produces $3$ times enlarged image of an object placed $10 \mathrm{cm}$ in front of it. Calculate its radius of curvature.

Select the correct alternative from those given below each statement and write the completed statement :

The power of a convex lens is $+4 \mathrm{D}$, then its focal length will be ______.

In a Solar Furnace, sunlight is concentrated at the ________ of the concave mirror.

A ray of light travelling in air enters obliquely into a glass slab. Does the ray move towards the normal or away from it?

Name the law represented by the formula: $n=\frac{\sin \mathrm{i}}{\sin \mathrm{r}}$