15.A ray of light is incident on a slab as shown in figure. The refractive index of medium of slab changes as =1+ y. The angle made by ray with x-axis at y = 2 is 30 0 air 2 (1)37 (3) 60 (2) 30 (4) 45 16.A uniform rod, of mass m, length I and r radius of cross section, is rotated about an axis passing through one of its ends and perpendicular to its length with constant angular velocity w in horizontal plane. If Y is the Young's modulus of the material of rod, the increase in its length due to rotation of rod is mw (1) mw212 (3) 3rY mw212 (2) 2m 2mw212 (4) shiksina 17.A free particle having one electronic charge with initial kinetic energy 9 eV and de Broglie wavelength 1 mm enters a region of Vo potential difference such that new de Broglie wavelength is now 1.5 mm. Then eVo is (1) 5 eV (3) 13.5 eV (2) 6 eV (4) 15 eV 18.A sine wave is travelling in a medium. The minimum distance between the two particles, always having same speed, is (1) (2) 11 (3) 2 (4)