Physics 222 Modern Physics s1

Homework Set #6

Due Friday 3/24/06

Instructions

You are responsible for your own homework solutions. Consider these problems as practice for the exam. Consult me or other students when you have questions, but try to work the problems by yourself as much as you can. Collaboration is allowed, but you must indicate your collaborators, both in the class and outside of it.

For every problem, show all your work. Simply writing down a final answer without showing your reasoning and calculations is unacceptable. Draw diagrams and sketches for problems, where useful. For any essay type questions, make sure to use complete sentences.

Problem 33: Consider the schematic diagram shown, with two 1.5 V batteries and three non-identical light bulbs. In this circuit, Bulb 1 has a resistance of 1 W, Bulb 2 has a resistance of 2 W, and Bulb 3 has a resistance of 3 W. Use any of the Loop Rule, Junction Rule, and Resistance Rule to figure out the potential difference (voltage drop) across each bulb and the current through each bulb.

Problem 34: In Group Exercise #25, you observed that a copper penny would not be attracted to a magnet, nor could the penny be magnetized. You also observed that an iron nail was strongly attracted to a magnet, and that the nail could be magnetized with the point of the nail being a N pole and the head of the nail being a S pole. You could just as easily magnetize the nail so that the point of the nail was a S pole and the head of the nail was a N pole. Explain these various observations, using the ideas of ferromagnetism, magnetic polarization, and magnetic domains.

Problem 35: (based on Chapter 11, Exercise 6, p. 386). During our group exercises, you often needed a nail that was initially demagnetized. Your instructor was able to demagnetize some nails by banging on them very hard. Hammering or heating a magnet can demagnetize it. What happens to the magnetic domains inside the magnet during these processes?

Problem 36: In Group Exercise #26, you made magnetic fields without using magnets. At the end of that group exercise were several questions that you should answer here: Do currents create magnetic fields? What’s your evidence? How would you convince someone who isn’t in our class of your conclusion?

Problem 37: As part of Group Exercise #27, you observed some demonstrations with a solenoid, an iron core, and a permanent magnet.

a) The (unmagnetized) iron core was placed such that a little bit of the core was inside the solenoid. When current ran through the solenoid, the iron core moved further inside the solenoid. Using some combination of words and sketches, explain how/why this happened.

b) When the permanent magnet was placed inside the solenoid in a particular orientation, the magnet shot out of the solenoid when current ran through the solenoid. Again, using some combination of words and sketches, explain how/why this happened.

Problem 38:

Chapter 11, Exercise 42, p. 387

Problem 39: In Group Exercise #28, you observed the deflection of the electron beam in a cathode ray tube due to the magnetic field of a permanent magnet. If you hold a magnet so that the S pole end is up and bring it near the cathode ray tube from underneath (in the Group Exercise, you brought the magnet near the CRT from above and from the sides, but not from underneath), what direction will the electron beam deflect? Make sure your answer and explanation includes a sketch.