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Download How Things Work Homework 10
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How Things Work Homework 10 Due: Tuesday, December 1st, 2015 NOTICE THAT THERE ARE TWO PAGES ON THIS ASSIGNMENT Conceptual Questions: 1. Chapter 11. Exercise 20 2. The figure represents an electromagnetic brake that uses eddy currents. An electromagnet hangs from a railroad car near one rail. To stop the car, a large current is sent through the coils of the electromagnet. The moving electromagnet induces eddy currents in the rails, whose fields oppose the change in the electromagnet’s field. The magnetic fields of the eddy currents exert force on the current in the electromagnet, thereby slowing the car. The direction of the car’s motion and the direction of the current in the electromagnet are shown correctly in the picture. Determine whether one or the other or both of the eddy currents shown on the rails is/are correct. Explain your answer. 3. Why does an iron core increase the magnetic field produced by a coil of wire? (I.e., the iron is located in the middle of the coil.) 4. If you place a metal ring in a region in which a magnetic field is rapidly alternating, the ring may become hot to your touch. Why? 5. Why is it dangerous to touch the terminals of a high-voltage capacitor even after the voltage source that charged the capacitor is disconnected from the capacitor? (b) What can be done to make the capacitor safe to handle after the voltage source has been removed? Quantitative Questions: 6. What is the current delivered by the power supply for the circuit on the right? 7. As a person moves about in a dry environment, electric charge accumulates on the person’s body. Once it is at high voltage, either positive or negative, the body can discharge via sparks and shocks. Consider a human body isolated from ground, with the typical capacitance 150 × 10−12 𝐹. (a) What charge on the body will produce a potential of 10,000V? (b) Sensitive electronic devices can be destroyed by electrostatic discharge from a person. A particular device can be destroyed by a discharge releasing an energy of 0.25 J. To what voltage on the body does this situation correspond?