Magnets PDF

## Magnets Magnets have many effects, sometimes surprisingly strong. They have many uses including computer hard drives, loudspeakers, credit card strips, magnetic fasteners and compasses for navigation. Even though satellite navigation is very effective, ships and aircraft still carry navigation c...

## Magnets Magnets have many effects, sometimes surprisingly strong. They have many uses including computer hard drives, loudspeakers, credit card strips, magnetic fasteners and compasses for navigation. Even though satellite navigation is very effective, ships and aircraft still carry navigation compasses. ### Magnetic forces Magnetism is an example of a non-contact force. Magnets exert a force on the region around them. A magnet will attract any magnetic materials that are close enough. They do not need to be touching to have an effect. There are three magnetic elements: - iron - nickel - cobalt Many alloys of iron are also magnetic, including most types of steel. Magnets have two ends, called poles. These are the north-seeking pole (N) and the south-seeking pole (S). 1. What type of force is magnetism? 2. List four magnetic materials. 3. Name the two poles that magnets have. ### Attracting and repelling If two magnets are brought together, the effect will depend on their positions: - north to north repels - south to south repels - north to south attracts. - Describe the rules about magnets attracting and repelling each other. - Describe what will happen in each of these situations: - The N pole of a magnet is brought towards the S pole of another magnet. - The S pole of a magnet is brought towards a piece of magnetised iron. - The N pole of a magnet is brought towards a piece of copper. - Explain why a magnet hanging on a thread will respond to magnetic forces more easily than a magnet laying on a bench. ### Effects of magnets Magnets exert a force in the region around them and the effect can be detected with a magnetic compass. Normally, a compass needle orientates itself in line with the Earth's magnetism, but close to a magnet the force exerted is greater than the Earth's magnetism. As a magnet is brought towards a compass from a distance there comes a point when the needle is no longer in line with the Earth's magnetism. The stronger the magnet, the larger the region around it that will be affected. 1. Explain, using examples including magnetism, the differences between contact and non-contact forces. 2. Someone states that 'magnets stick together'. What would be a better explanation of the behaviour of magnets? ### Understanding magnetic fields Magnetic materials in the region around a magnet experience a magnetic force. The Earth behaves as a gigantic magnet that attracts particles from outer space towards the North and South Poles. As these particles enter the Earth's atmosphere they cause an amazing natural light display. #### Magnetic fields A magnetic field is the space around a magnet where its magnetic field works. Within the field, magnetic materials such as iron are attracted. Other magnets can be attracted if unlike poles are close enough or repelled if like poles are close enough. Sprinkling iron filings around a magnet shows the magnetic field. Each of the filings becomes a tiny magnet that lines up with the field, because of magnetic forces acting on it. The arrangement of the filings shows the magnetic field lines. The closer the lines of magnetic force are to each other, the higher the strength of the magnetic field. The direction of the field lines is the direction in which a magnetic north pole would move if placed in the field - from north (N) towards south (S). This is the way a compass would point. 1. What does the pattern of iron filings around a magnet show? What does it not show? 2. Why are the lines of force closer together near the magnet poles? 3. Tiny fragments of substances other than iron could be used to show the force lines in a magnetic field. Choose which ones would work from this list: scraps of paper, steel, pepper, plastic, sawdust, nickel, house dust, copper, carbon. ### The Earth's magnetic field The Earth's core contains materials that are rich in iron. Around a solid inner core is a molten outer core. Scientists believe that currents within the molten core create a magnetic field as they flow around. Two well known effects of the Earth's magnetic field are: - Magnets line up in a N to S direction, if they are free to turn. This is how a compass works. - The Aurora Borealis (Northern Lights). Charged particles entering Earth's atmosphere are attracted to the magnetic poles. As they collide with the gas particles in the atmosphere an amazing natural light display is created. The Earth also has a gravitational field, which is the region around the Earth where the force of gravity acts. The gravitational field attracts all masses, whereas only particular materials are affected by the magnetic field. You will learn more about the Earth's magnetic field in Chapter 6. * Why does the Earth have a magnetic field around it? * Describe similarities and differences between magnetism and gravity. * How can evidence be collected to find out whether other planets have magnetic fields? ### The magnetic field model Scientists often use models to try to represent things that are hard to see or understand. A model can be a simplified version, a description or a picture. Figure 2.5.3c shows a model that represents the Earth's magnetic field. It is useful because it helps us to understand something we cannot see. Many models do not represent reality exactly and scientists need to be aware of the weaknesses of the models they use. * Explain, using examples, why scientists use models. * Evaluate the Figure 2.5.3c as a model of Earth's magnetism. What are its strengths and weaknesses?