Which feature of electromagnets makes them more useful than permanent magnets in many modern technologies?
O A. The current can be adjusted to control the strength of the
magnetic field.
B. The strength of the magnetic field is more consistent in
electromagnets.
O C. Electromagnets are not dependent on a power supply.
O D. Electromagnets cannot be turned on and off.

Why there is no inductive reactance in dc circuits

Ateam of astronauts is on a mission to land on and explore a large asteroid. in addition to collecting samples and performing experiments, one of their tasks is to demonstrate the concept of the escape speed by throwing rocks straight up at various initial speeds. with what minimum initial speed vesc will the rocks need to be thrown in order for them never to "fall" back to the asteroid? assume that the asteroid is approximately spherical, with an average density p 3.84 x108 g/m3 and volume v 2.17 x 1012 m3 recall that the universal gravitational constant is g 6.67 x 10-11 n m2/kg2

The free body diagram shows a box being pulled to the left up a 25-degree incline. the magnitude of the normal force is