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Chapter 28 – Magnetic Fields Book Web Site: KineticBooks (It’s your responsibility not to forget your email & password!) Reading Assignment Only Through Section 6 End of Chapter Problems (Online Homework) Prior Knowledge Vocabulary Magnet Pole Ferromagnetism Magnetic Field Compass Lodestone Declination Equations None 28.0 – Introduction 28.0.1 What are the two poles of a magnet called? North & south 28.0.2 Read Carefully, what does the introduction say about the Earth’s Magnetic field, (is this surprising)? Scientists cannot say for certain the REASON for earth’s magnetic field and why it switches poles once in a while (millions of years) 28.1 – Magnetic Fundamentals 28.1.1 How do magnetic poles attract and repel? (Does north attract north or south, what about vice versa…) Opposites attract; like repel 28.1.2 What is the strongest and most frequently found type of magnetism? Ferromagnetism (iron-like) 28.1.3 Can a magnet stick to a surface that isn’t magnetic…why? surface…why? Can a magnet stick to any No. It must “induce” (create) a magnetic field from the door’s surface. Only surfaces made of ferromagnetic materials. 28.1.4 What happens if you chop a magnet in half? Can you separate magnetic poles? No. It doesn’t have to be in “half” either. Each END created will be a new pole. 28.2 – Magnetic Fields 28.2.1 We use the symbol E to symbolize electric field, what symbol do we use for magnetic field? B 28.2.2 What unit do we measure magnetic field in? Tesla (also Gauss) 28.2.3 Electric field starts at the positive charge and ends at the negative charge, what about magnetic field (which pole does it start and end at)? North and goes south (N S) 28.2.4 Can I draw a magnetic field line, or only magnetic field loops? Loops (the closer together, the stronger) 28.2.5 Take a guess…how does the magnetic field of an object (and the magnetic force) change with distance (think about electric fields)? Inversere square (decreases) 28.3 – Physics at Work: Lodestones 28.3.1 What is a lodestone? A naturally magnetic rock that retains it’s magnetic field for a long time 28.3.2 Why might you think that lodestones are important historically? The helped Columbus find America! 28.4 – The Earth and Magnetic Fields 28.4.1 Give a continent (geographically) that might be the center of the Earth’s north magnetic pole. Antarctica 28.4.2 What is the approximate strength of the Earth’s magnetic field? 5 x 10-5 T 28.4.3 Is the Earth’s magnetic field a constant? What is happening with it? No. It’s decreasing. 28.5 – Physics at Work: Compasses and the Earth 28.5.1 Explain what a compass is? A magnetic direction-finding & location device 28.5.2 What is declination? The difference in angles between north & magnetic south poles 28.5.3 How could you measure latitude with a free standing compass? See how far downward the needle points. 28.6 – Ferromagnetism 28.6.1 What is magnetic domain? A magnetic domain is a small section of a ferromagnetic material in which the atoms in this section are magnetically aligned. Adjoining domains will tend to be aligned magnetically in the same way if the material is magnetized, but this tendency does not exist for domains in samples that are not magnetized. 28.6.2 Why are most materials non-magnetic? The spins in the electrons are balanced with other electrons spinning the opposite way; or, the material is warm enough that atoms move around too much to ever align magnetically. 28.6.3 What happens when a ferromagnetic material is subjected to an external magnetic field? The individual domains tend to align with that field. 28.6.4 Why doesn’t an un-magnetized ferromagnetic material (like iron) go back to this un-magnetized state after being subjected to an external magnetic field? It does tend to go back depending on the amount of exposure time within the field and the strength of the field. 28.23 - Gotchas Try to create three multiple choice questions (remember, if they’re really good you could see them on a test!) 28.24 - Summary Add some of your own notes to the summary. (Don’t just copy the summary word for word!)