Y8 Magnetic Field PDF

Understanding MM.DD.YY magnetic field Lorem Ipsum Magnetism - a non contact force One of the important points to remember is that magnetic forces can act between objects that are not touching. In this lesson, we will explore a phenomenon called the magnetic field, which explains h...

Understanding MM.DD.YY magnetic field Lorem Ipsum Magnetism - a non contact force One of the important points to remember is that magnetic forces can act between objects that are not touching. In this lesson, we will explore a phenomenon called the magnetic field, which explains how magnets can affect objects they are not touching. Learning objectives Explain what a magnetic field is. Outline how magnetic flux lines convey information about the strength of the magnetic force. Name the principle that allows magnetic fields to interact. Draw simple magnetic fields, such as the magnetic field of a bar magnet. Magnetic field 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 field A magnetic field is the area around the magnet where there is a magnetic force. We use magnetic flux lines (also called magnetic field lines) to show the magnetic field around a magnet. You can actually see the magnetic flux lines if iron filings are scattered around the magnet! The image below shows what happens if you scatter iron filings onto a sheet of clear plastic above a bar magnet. The iron, being a magnetic material, will align to the patterns of the field lines. Think, Pair and Share What does the pattern of iron filings around a magnet show? What does it not show? Why are the lines of force closer together near the magnet poles? 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. Magnetic field lines Magnetic flux lines always come out of the north pole of a magnet and go into the south pole. This means that for bar magnets, the magnetic field comes out of the north pole then curves around to enter the south pole. Strength of magnetic field the strength of the magnetic field is represented by how close together the magnetic flux lines are. When the lines are close together, it means that the magnetic field is strong. When they are spread apart, the magnetic field is weak. For example, in the diagram below, you can see that the magnetic flux lines are much closer together near the poles than on the sides of the bar magnet. 1 - minute table task Quick quiz 1. Recall which pole magnetic flux lines come out of. 2. Recall which pole magnetic flux lines go into. 3. Select what it means if the magnetic flux line a. are close together. b. are spread apart. i. The magnetic field is unstable ii. The magnetic force is weak iii. The magnetic force is strong iv. The magnetic force is about to explode Practical: Work in pairs or in threes Interactions between two magnets When two magnets are close together, their magnetic fields interact. If the magnetic fields of two magnets are pointing in the same direction, the fields will add together. This means that the magnetic force will be stronger. In this scenario, the magnetic flux lines come out of one magnet's north pole and go into the other magnet's south pole. This creates a very strong magnetic force between the two magnets, so they are attracted to each other. Repulsion of like poles If the fields point in opposite directions, they will cancel out. This will make the magnetic force weaker. In these diagrams, the magnetic flux lines are either both flowing inwards or both flowing outwards. This causes the magnetic fields to interact in such a way that the magnets are repelled. Practical: Work in pairs or in threes The earth’s magnetic field Without the Earth’s magnetic field there would be no life on this planet. It protects us from deadly charged particles carried in solar winds from the Sun. How does it do this and what causes the Earth’s magnetic field to exist? Did you know...? The planet Mercury also has its own magnetic field. However, it is not as strong as the Earth’s and, because it is closer to the Sun, solar winds cause much more damage to its surface. The earth’s magnetic field All compasses respond to magnetic fields. The fact that they all line up in a north–south direction (when not near a magnet) is evidence that the Earth must have its own magnetic field. The N pole of a magnetic compass needle points in a geographical north direction, wherever it is on Earth. This is evidence that the Earth’s geographic North Pole is actually the Earth’s magnetic S pole, or very close to it We also know from magnetic rocks that the poles of the Earth’s magnetic field are not fixed, but reverse every few hundred thousand years. The earth’s magnetic field 1. Why does the Earth have a magnetic field around it? 2. Describe similarities and differences between magnetism and gravity. 3. How can evidence be collected to find out whether other planets have magnetic fields? Discuss with a seatmate Summarise the evidence for the Earth’s magnetic field. Task The geodynamo theory Evidence about the structure of the centre of the Earth has largely come from earthquakes, volcanoes and rocks. Scientists believe the centre of the Earth is made from a core of solid iron, surrounded by a liquid core of iron and nickel. The spinning action of the Earth causes the liquid core to spin in a regular way. This movement causes charged particles to move, forming small currents. Electric currents produce magnetic fields and so magnetic domains within the liquid develop, lining up to create a weak magnetic field. This is called the geodynamo theory. Why can we not be certain about how the Earth’s magnetic field works? The impact of the earth’s magnetic field