JiTT Exercises

Please Note: It may not always be possible to include the necessary special characters, superscripts, subscripts, etc. in e-mail responses to this group of exercises. We suggest that you discuss this matter with your professor/class and decide upon a system for indicating such characters. You may cut/paste some characters and/or Greek letters from Microsoft Word, using the Insert menu. Alternatively, we suggest that you agree upon abbreviations for or spell out symbols, Greek letters, or characters and indicate superscripts and subscripts by using "sup", "sub", or up/down carats.


1			Two identical circular coils of wire are separated by a fixed center-to-center distance. Describe the orientation of the coils that would (a) maximize or (b) minimize their mutual-inductance.




2			A 2-m-long copper pipe is held vertically. When a marble is dropped down the pipe, it falls through in about 0.7 s. A magnet of similar size and shape dropped down the pipe takes much longer. Why?




3			A circular loop of wire can be used as an antenna to sense the changing magnetic fields in an electromagnetic wave (such as a radio transmission). What is the advantage of using a coil with many turns rather than a single loop?




4			In Fig. 20.1, what would the magnitude (in terms of v, L, R, and B) and direction (CW or CCW) of the current be if the direction of the magnetic field were: (a) into the page; (b) to the right (in the plane of the page); (c) up (in the plane of the page); (d) such that it has components both out of the page and to the right, with a 20.0° angle between the field and the plane of the page? Fig. 20.1




5			In Fig. 20.46, switch S is initially open. It is closed, and then opened again a few seconds later. (a) In what direction does current flow through the ammeter when switch S is closed? (b) In what direction does current flow when switch S is then opened? Fig. 20.46




6			Two loops of wire are next to each other in the same plane (Fig. 20.49). (a) If the switch S is closed, does current flow in loop 2? If so, in what direction? (b) Does the current flow for only a brief moment, or does it continue? (c) Is there a magnetic force on loop 2? If so, in what direction? (d) Is there a magnetic force on loop 1? If so, in what direction? Fig. 20.49




7			A step-down transformer has a turns ratio of 1/100. An AC voltage of amplitude 170 V is applied to the primary. If the primary current is 1.0 mA, what is the secondary current?




8			The primary coil of a transformer has 250 turns; the secondary coil has 1000 turns. An alternating current is sent through the primary coil. The emf in the primary is 16 V. What is the emf in the secondary?




9			An ideal solenoid has length l. If the windings are compressed so that the length of the solenoid is reduced to 0.50 l, what happens to the inductance of the solenoid?




10			The current in a 0.080-H solenoid increases from 20.0 mA to 160.0 mA in 7.0 s. Find the average emf in the solenoid during that time interval.




11			In Fig. 20.52, after the switch has been closed for a long time, it is opened. How long does it take for the energy stored in the inductor to decrease to 0.10 times its initial value? Fig. 20.52




12			A uniform magnetic field of magnitude 0.29 T makes an angle of 13° with the plane of a circular loop of wire. The loop has radius 1.85 cm. What is the magnetic flux through the loop?




13			How much energy due to the Earth's magnetic field is present in 1.0 m³ of space near Earth's surface, at a place where the field has magnitude 0.45 mT?

Your Results:

E-mail Your Results