Magnetism Short Notes

Magnetism: Properties of Magnets ● A magnet is any material that attracts iron and materials that contain iron. ● Magnets have many modern uses, but they are not new. ● More than 2,000 years ago, people living in ancient Greece discovered an unusual kind of rock. ● This kind of rock contained a mineral called magnetite. ● Rocks containing magnetite attracted materials that contained iron. They also attracted or repelled other magnetic rocks. ● The attraction or repulsion of magnetic materials is called magnetism. A Natural Magnet: Some magnets are found in nature. This rock attracts iron nails because it contains the magnetic mineral called magnetite. ● Magnets have the same properties as magnetic rocks. ● Magnets attract iron and materials that contain iron. ● Magnets attract or repel other magnets. ● In addition, one part of a magnet will always point north when allowed to swing freely. Modern Magnets: Magnets come in a variety of shapes and sizes, but they share certain characteristics. Inferring What substance might the scissors, paper clips, and spoon have in common? Magnetic Poles ● Any magnet, no matter what its shape, has two ends, each one called a magnetic pole. ● The magnetic effect of a magnet is strongest at the poles. ● The pole of a magnet that points north is labeled the north pole. ● The other pole is labeled the south pole. ● A magnet always has a pair of poles, a north pole and a south pole. ● Magnetic poles that are unlike attract each other, and magnetic poles that are alike repel each other. ● The attraction or repulsion between magnetic poles is magnetic force. ● A force is a push or a pull that can cause an object to move. ● A magnetic force is produced when magnetic poles interact Magnetic Fields ● A magnetic force is strongest at the poles of a magnet, but it is not limited to the poles. ● Magnetic forces are exerted all around a magnet. ● The area of magnetic force around a magnet is known as its magnetic field. ● Because of magnetic fields, magnets can interact without even touching. ● The picture shows the magnetic field of a bar magnet. Notice the red lines, called magnetic field lines, around the magnet. ● Magnetic field lines are invisible lines that map out the magnetic field around a magnet. ● Magnetic field lines spread out from one pole, curve around the magnet, and return to the other pole. ● The lines form complete loops from pole to pole and never cross. Arrows are used to indicate the direction of the magnetic field lines—always leaving the north pole and entering the south pole. ● The distance between magnetic field lines indicates the strength of a magnetic field. ● The closer together the lines are, the stronger the field. ● A magnet’s magnetic field lines are closest together at the poles. Review Questions: 1. What is a magnet? - A magnet is any material that attracts iron and materials that contain iron. 2. What are three properties of a magnet? - A magnet attracts materials that contain iron, attracts or repels other magnets, and has one pole that points north when allowed to freely swing. 3. What will happen to a bar magnet that is allowed to swing freely? - The bar magnet will align itself in a north-south direction. 4. What area of a magnet has the strongest magnetic effect? - A magnet’s poles have the strongest effect. 5. How does a magnets north pole behave when brought near another magnets north pole? What about north pole near a south pole? - North pole to north pole repel each other, north pole to south pole attract. 6. What is a magnetic field? - The area of magnetic force around a magnet.