A low-voltage device like an electric bell obtains its electricity from a 120 V source, but requires only 4–8 V. Thus,it requires a small transformer. This often takes the form of an autotransformer, which has only one winding around a single core. Part of the winding forms the secondary coil, and the entire winding forms the primary coil. The autotransformer in the ?gure is 10 cm in length and has 100 windings. If the input voltage V1 is 120 V and the output voltage V2 is to be 6 V, how far apart should the contacts for the secondary coil be placed?