20.1 Magnetic Fields, Field Lines, and Force

• Certain parts of these rocks attracted bits of iron or other magnetic rocks more strongly than other parts. These areas are called the poles of a magnet.
• A magnetic pole is the part of a magnet that exerts the strongest force on other magnets or magnetic material, such as iron.
• The pole of the magnet that orients northward is called the north pole, and the opposite pole of the magnet is called the south pole
• Because magnets always have two poles, they are referred to as magnetic dipoles—di means two
• Only certain materials, such as iron, cobalt, nickel, and gadolinium, exhibit strong magnetic effects. Such materials are called ferromagnetic, after the Latin word ferrum for iron.
• Not only do ferromagnetic materials respond strongly to magnets—the way iron is attracted to magnets—but they can also be magnetized themselves—that is, they can be induced to be magnetic or made into permanent magnets
• A permanent magnet is simply a material that retains its magnetic behavior for a long time, even when exposed to demagnetizing influences
• Regions within the material called domains act like small bar magnets
• There is a well-defined temperature for ferromagnetic materials, which is called the Curie temperature, above which they cannot be magnetized.
• A magnet creates a magnetic field around it that describes the force exerted on other magnets placed in the field.
• An electromagnet is a device that uses electric current to make a magnetic field
• Applied to a straight current-carrying wire, the right-hand rule says that, with your right thumb pointed in the direction of the current, the magnetic field will be in the direction in which your right fingers curl
• The result is a wire coil. This is called a solenoid.
• These effects all fall under the umbrella of electromagnetism, which is the study of electric and magnetic phenomena