1. The U.S. Navy has proposed the use of extremely low frequency (ELF) electromagnetic waves for communication. Such waves could penetrate the oceans to reach distant submarines. To receive the signals the submarines would need quarter-wavelength antennae. Calculate a quarter-wavelength for an ELF wave with a frequency of 75 Hz (a) in air and (b) in water (n = 1.33). 2. Find the speed of light in flint glass which has an index of refraction n = 1.66