1. The problem statement, all variables and given/known data You need to use your cell phone which broadcasts an 830 MHz signal but you're in an alley between two massive radio wave absorbing building that have only a 15m space between them. What is the angular width in degrees of the electromagnetic wave after it emerges from between the buildings. 2. Relevant equations a sinO = (pd)/a a = slit width - 15m sinO = sine of theta, couldn't figure out how to do theta - unknown p = the number for the central maximum or minimum - 1? d = wavelength (didn't know how to do lambda either) - .361m 3. The attempt at a solution There's a basic element I'm missing here. I determined wavelength by dividing the speed of light by the frequency. So I then divide wavelength by the slit width of 15m and get an even smaller number that leads to an extremely small angle after I take the arcsine that seems unreasonable given the dimensions involved in this problem. The book comes up with an answer of 2.9 degrees. There's got to be something basic to this problem I'm missing, but I can't figure out what. Can somebody give me a nudge in the correct direction?