Q. Parallel beam of light from a He-Ne laser, with a wavelength of 652 nm, falls on two very narrow slits 0.050 mm apart. How far apart are the fringes in the center of the pattern on a screen 2.7 m away?
Q. A 210 km long high-voltage transmission line 2.0 cm in diameter carries a steady current of 960 A. If the conductor is copper with a free charge density of 9.0 x10^28 electrons per cubic meter, how many years does it take one electron to travel the full length of the cable?