চিত্রানুযায়ী $CD=1,\ CO=X$ও আলোর বেগ=$v,\ A$ হতে $B$ তে পৌঁছাতে সময় $t$ হলে,

চিত্রে  ফার্মাটের নীতি অনুযায়ী সঠিক সময় হল-

When a picture drawn on paper is seen through a slab of a transparent materials of thickness $5cm$, it appear to be raised by $1.5 cm$. Critical angle at the boundary of this transparent material and air is

A fish is a little away below the surface of a table. If the critical angle is $49^o$, then the fish could see things above the water surface within an angular angle of

A vessel contains water up to a height of $20\ cm$ and above it an oil up to another $20\ cm$. The refractive indices of the water and the oil are $1.33$ and $1.30$ respectively. Find the apparent depth of the vessel when viewed from above.

জলাশয়ের তলদেশ উহার প্রকৃত গভীরতার কতটুকু ?