1. A card containing two slits separated center-to-center by 0.1mm, is illuminated by a red laser (lambda = 632:82nm). If the fringes on an observing screen are to be 10mm apart, how far away (in m) should the screen be?

2. Two parallel slits 0.1mm apart are illuminated and it is found that the fifth bright fringe is at an angle of 1.2 degree. Determine the wavelength of the light (in nm).

3. Two 1MHz radio antennas emitting in-phase are separated by 600m along a north-south line. A radio placed 20km east is equidistant from both transmitting antennas and picks up a fairly strong signal. How far north (in km) should that receiver be moved if it is again to detect a signal nearly as strong.