Una rapidez de 7 mm/us es igual a: a) 7000m/s b) 70 m/s c) 7 m/s d) 0.07 m/s

For this conversion you should know that 1 meter has 1000 millimeters and that 1s equals 1000000 micro seconds, then:

7mm/us * 1m/1000mm * 1000000us/1s = 7000 m/s

The mm are canceled just like the micro seconds and the result remains in m / s .

Therefore option A is correct

A) 7000m / s

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.