I have just done an experiment of magnetic fields around electric current in straight wire by using the seach coil. I have 2 questions about this... (1)why is this necessary to ensure the search coil is at the same level as the wire? My anwser:If the seach coil is not at the same level as the wire, the measurement is not correct. It is because the induced e.m.f. is the greatest around the wire. We should put the seach coil at the same level to have a clear measurement of induced e.m.f. (2)why the sensitivity of the seach coil can be increased by increasing the frequency? My anwser:If the frequency increased, the current changed its direction more frequently. Thus, the induced e.m.f will increase. As a result, the seach coil had a increase in sensitivity. Am I correct??