Which has frequency below the audible range? (a) ultrasonic (b) supersonic (c) infrasonic (d) all of these

Place me with this question is my last question

The magnitude of the magnetic field at a certain distance from a long, straight conductor is represented by b. what is the magnitude of the magnetic field at twice the distance from the conductor? a. at twice the distance, the magnitude of the field is 4b.b. at twice the distance, the magnitude of the field is 2b.c. at twice the distance, the magnitude of the field is b/2.d. at twice the distance, the magnitude of the field is b/4.e. at twice the distance, the magnitude of the field remains equal to b.

Smallest intensity of a stimulus that you can detect 50 percent of the time is