Questions

A periscope is an optical instrument that uses a system of prisms, lenses, or mirrors to reflect images through a tube.

Light from a distant object strikes the top mirror and is then reflected at an angle of 90 degrees down the periscope tube. At the bottom of the periscope, the light strikes another mirror and is then reflected into the viewer’s eye.

Hence, A periscope works by the principle of Total internal reflection.

A book has a spine to hold all the pages, but it has no bones.

The sentence is grammatically and contextually correct. This is because, the verb, ‘to look forward to’ means toanticipate. It requires a direct object and it will be the gerund form of the verb i.e. ‘meeting’. Thus, the correct formation would be, ‘My brother is looking forward to meeting his employer tomorrow’.

Let their edges be a and b. Then,

a3/b3 = 1/27 (or) (a/b)3 = (1/3)3 (or) (a/b) = (1/3).

\Ratio of their surface area = 6a2/6b2 = a2/b2 = (a/b)2 = 1/9, i.e. 1:9.