50cm\(^3\) of air at a pressure of 5Nm\(^{-2}\) is enclosed in a metal tube by a piston. If the piston is pushed in a distance of 10cm, what will the pressure of the air become, if the cross-sectional area of the tube is 2cm\(^{-2}\)? (Assume that the temperature remains constant throughout)

Totally reflecting prisms are preferred to mirrors in periscopes because

I. mirror gives multiple images
II. silvering on mirrors is easily damaged
III. mirrors reflect less light than totally reflecting prisms