Unit 3 Lesson 4 Magnets and Magnetism. Copyright Houghton Mifflin Harcourt Publishing Company

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2 Stuck on You What are some properties of magnets? The term magnet describes any material that attracts iron or objects made of iron. Many magnets are made of iron, nickel, cobalt, or mixtures of these metals. When you bring two magnets together, they exert a push or pull on each other called a magnetic force. Magnetic force is one of only three forces in nature that can act at a distance electrostatic force and gravity are the other two.

3 What are some properties of magnets? Magnetic force results from spinning electric charges in the magnets. The force can either push the magnets apart or pull them together. Two magnets can push each other apart because of their ends, or magnetic poles. Every magnet has a north pole and a south pole. If you place the north poles of two magnets together, they will repel, or push away. If you place the north pole and the south pole of two magnets near each other, they will attract, or come together.

4 What are some properties of magnets? The area surrounding a magnet where magnetic forces can be detected is called the magnetic field. A magnetic object placed anywhere in the magnetic field will be affected by the magnet. A magnet s magnetic field is strongest near its poles. The greater the distance from the poles, the weaker the magnetic field.

5 What are some properties of magnets? Magnetic field lines enter a magnet at the south pole and exit at the north pole.

6 When Everything Lines Up What causes magnetism? Whether a material is magnetic or not depends on the material s atoms. As an electron moves in an atom, it makes, or induces, a magnetic field. The electron will then have a north and a south magnetic pole. In most atoms, such as copper and aluminum, the magnetic fields of the individual electrons cancel each other out. These materials are not magnetic.

7 What causes magnetism? The magnetic fields of the electrons in iron, nickel, and cobalt atoms do not completely cancel each other out. As a result, atoms of these materials have small magnetic fields. These materials are magnetic. In materials such as iron, nickel, and cobalt, groups of atoms form tiny areas called domains. The north and south poles of the atoms in a domain line up and make a strong magnetic field.

8 What causes magnetism? The domains in an object determine whether the object is magnetic. When a magnetic material is placed in a magnetic field, most of the domains point toward the same direction, forming a magnetic field around the entire object. In other materials, there are no domains to line up because the atoms have no magnetic fields. These materials cannot become magnetized.

9 What causes magnetism? Which image shows an object s domains before magnetization, and which shows the object s domains after magnetization?

10 What are some types of magnets? Some materials, such as soft iron, can be made into magnets temporarily when placed in a strong magnetic field. The material s domains line up, and the material is magnetized. Permanent magnets are difficult to make, but they keep their magnetic properties longer. A material that can be turned into a magnet is called ferromagnetic. A ferromagnetic material can be turned into a permanent magnet when placed in a strong magnetic field.

11 What are some types of magnets? An electromagnet is an iron core wrapped with electrical wire. When an electric current is in the wire, a magnetic field forms. When the current is turned off, the magnetic field stops. The strength of an electromagnet depends on the strength of the electric current.

12 Polar Opposites How is Earth like a giant magnet? Earth has a magnetic field. Earth also has a north magnetic pole and a south magnetic pole.

13 How is Earth like a giant magnet? Scientists now think that Earth s inner structure produces its magnetic field. Earth s inner core is made of solid metals. Earth s outer core is made of liquid iron and nickel, which are ferromagnetic. As Earth rotates, the liquid outer core moves. Charged particles, including electrons, move in the liquid and form a magnetic field. The constant rotation keeps Earth magnetized.

14 How is Earth like a giant magnet? Earth s magnetic field is strongest near its poles, which can attract other magnets, such as the needle of a compass. The north pole of a magnet gets its name because it points toward Earth s geographic North Pole. How can the north end of a compass point to the north magnetic pole? A better term for the north pole of a magnet would be a north-seeking pole. Using these terms, the magnetic pole near Earth s North Pole is considered the south pole of a magnet.

15 How is Earth like a giant magnet? Earth s magnetic poles are not the same as Earth s geographic poles. The geographic poles mark the ends of Earth s axis. The geographic poles are near, but not exactly at, the magnetic poles.

16 What is an aurora? The beautiful displays of light that can be seen at northern or southern latitudes are related to Earth s magnetic field. The sun ejects charged particles. When they reach Earth, they are guided by its magnetic field. They enter Earth s upper atmosphere near the magnetic poles. There, the charged particles interact with atoms in the air, causing the atoms to emit visible light. This glow is called an aurora.