22.2 Ferromagnets and Electromagnets Ferromagnets Only certain materials, such as iron, cobalt, nickel, and gadolinium, exhibit strong magnetic effects. Such materials are called ferromagnetic, after the Latin word for iron, ferrum. A group of materials made from the alloys of the rare earth elements are also used as strong and permanent magnets; a popular one is neodymium. Other materials exhibit weak magnetic effects, which are detectable only with sensitive instruments. Not only do ferromagnetic materials respond strongly to magnets (the way iron is attracted to magnets), they can also be magnetized themselves that is, they can be induced to be magnetic or made into permanent magnets. Heat and tapping Fe bar SN S Figure 22.7 An unmagnetized piece of iron is placed between two magnets, heated, and then cooled, or simply tapped when cold. The iron becomes a permanent magnet with the poles aligned as shown: its south pole is adjacent to the north pole of the original magnet, and its north pole is adjacent to the south pole of the original magnet. Note that there are attractive forces between the magnets.

What is the direction of the magnetic field at point P? • P O into the page away from you O out of the page toward you O towards the top of the page O towards the bottom of the page

A straight wire carrying 3.8 A current is laid in a E-W magnetic field. When 85 cm of wire is in the field, the wire feels a force of 1.8 N. What is the strength of the magnetic field? • Do NOT include units • Round your answer to the hundredths place, include zeros if needed

A group of particles is traveling in a magnetic field of unknown magnitude and direction. You observe that a proton moving at 1.30 km/s in the +x-direction experiences a force of 2.10x10-16N in the +y-direction, and an electron moving at 4.50 km/s in the -z- direction experiences a force of 8.10x10-18 N in the +y-direction. • Part A You may want to review (Page) Part B For related problem-solving tips and strategies, you may want to view a Video Tutor Solution of Magnetic force on a proton. Part C What is the magnitude of the magnetic force on an electron moving in the -y-direction at 3.40 km/s ? Express your answer in newtons. ? F = N