A student used a PhET simulation to investigate factors that affect the strength of electromagnets. Which of the following is the best explanation of the position of the of the compass needle in the investigation? 10 + Magnete (B) Field B 480 C 3.30 G 3.57 G 20 By O The needle is aligned with the coll. The needle is aligned with the electrical field from the battery. The needle is aligned with the magnetic field from the coi. None of the above O

Cyclotrons are widely used in nuclear medicine for producing short-lived radioactive isotopes. these cyclotrons typically accelerate h- (the hydride ion, which has one proton and two electrons) to an energy of 5 mev to 20 mev. this ion has a mass very close to that of a proton because the electron mass is negligible—about 1 2000 of the proton’s mass. a typical magnetic field in such cyclotrons is 1.9 t. (a) what is the speed of a 5.0-mev h-? (b) if the h- has energy 5.0 mev and b = 1.9 t, what is the radius of this ion’s circular orbit?