CHAPTER 29 HOMEWORK
1. (p.752 Ex.10) The magnetic field perpendicular to a circular loop of wire 20cm in diameter is changed from +0.52T to -0.45T in 180ms, where + means the field point away from an observer and - toward the observer. (a) Calculate the induced emf. (b) In what direction does the induced current flow?
2. (p.752 Ex.19) The area of an elastic circular loop decreases at a constant rate, dA/dt = -3.50 x 10-2 m2/s. The loop is in a magnetic field B = 0.48T whose direction is perpendicular to the plane of the loop. At t = 0, the loop has area A = 0.285m2. Determine the induced emf at t = 0, and t = 2.00s.
3. (p.753 Ex. 25) A conducting rod rests on two long frictionless parallel rails in a magnetic field B (^ to the rails and rod) as in Fig. 29-35. (a) If the rails are horizontal and rod is given an initial push, will the rod travel at constant speed even though a magnetic field is present? (b) Suppose at t = 0, when the rod has speed v = vo, the two rails are connected electrically by a wire from point a to point b. Assuming the rod has resistance R and the rails have negligible resistance, determine the speed of the rod as a function of time . Discuss your answer.
4. (p.753 Ex.30) A simple generator has a 420-loop square coil 21.0cm on a side. How fast must it turn in a 0.350-T field to produce a 120-V peak output?
5. (p.754 Ex.42) The output voltage of a 100-W transformer is 12V and the input current is 26A. (a) Is this a step-up or a step-down transformer? (b) By what factor is the voltage multiplied?
6. (p.754 Ex.48) In Fig. 29-22c, draw two identical small circles, one placed near the center of the magnetic field region and the other near its edge (but not beyond the edge). Show that the emf around each circle is the same, even thou E is greater in the region of the outer circle.
7*. (p.753 Ex.27) A short section of wire, of length a, is moving with velocity v, parallel to a very long wire carrying a current I as shown in fig. 29-36. The near end of the wire section is a distance b from the long wire. Assuming the vertical wire is very long compared to a + b, determine the emf between the ends of the short section. Assume v is (a) in the same direction as I, (b) in the opposite direction to I.
8*. (p.754 Ex.45)If 65kW is to be transmitted over two 0.100-W lines, estimate how much power is saved if the voltaage is stepped up from 120V to 1200V and then down again, rather than simply transmitting at 120V. Assume the transformers are each 99 percent efficient.