Chapter 7: Q39P (page 339)
Suppose a magnetic monopole passes through a resistanceless loop of wire with self-inductance L . What current is induced in the loop?
Short Answer
The induced current in the loop is
Chapter 7: Q39P (page 339)
Suppose a magnetic monopole passes through a resistanceless loop of wire with self-inductance L . What current is induced in the loop?
The induced current in the loop is
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Get started for freeA perfectly conducting spherical shell of radius rotates about the z axis with angular velocity , in a uniform magnetic field . Calculate the emf developed between the “north pole” and the equator. Answer:localid="1658295408106" .
Prove Alfven's theorem: In a perfectly conducting fluid (say, a gas of free electrons), the magnetic flux through any closed loop moving with the fluid is constant in time. (The magnetic field lines are, as it were, "frozen" into the fluid.)
(a) Use Ohm's law, in the form of Eq. 7.2, together with Faraday's law, to prove that if and is J finite, then
(b) Let S be the surface bounded by the loop at time t , and a surface bounded by the loop in its new position at time t+dt (see Fig. 7.58). The change in flux is
Use to show that
(Where R is the "ribbon" joining P and P' ), and hence that
(For infinitesimal dt ). Use the method of Sect. 7.1.3 to rewrite the second integral as
And invoke Stokes' theorem to conclude that
Together with the result in (a), this proves the theorem.
A square loop of wire, with sides of length a , lies in the first quadrant of the xy plane, with one comer at the origin. In this region, there is a nonuniform time-dependent magnetic field (where k is a constant). Find the emf induced in the loop.
Question: The preceding problem was an artificial model for the charging capacitor, designed to avoid complications associated with the current spreading out over the surface of the plates. For a more realistic model, imagine thin wires that connect to the centers of the plates (Fig. 7.46a). Again, the current I is constant, the radius of the capacitor is a, and the separation of the plates is w << a. Assume that the current flows out over the plates in such a way that the surface charge is uniform, at any given time, and is zero at t = 0.
(a) Find the electric field between the plates, as a function of t.
(b) Find the displacement current through a circle of radius in the plane mid-way between the plates. Using this circle as your "Amperian loop," and the flat surface that spans it, find the magnetic field at a distance s from the axis.
Figure 7.46
(c) Repeat part (b), but this time uses the cylindrical surface in Fig. 7.46(b), which is open at the right end and extends to the left through the plate and terminates outside the capacitor. Notice that the displacement current through this surface is zero, and there are two contributions to Ienc.
A circular wire loop (radius r , resistance R ) encloses a region of uniform magnetic field, B , perpendicular to its plane. The field (occupying the shaded region in Fig. 7.56) increases linearly with timeAn ideal voltmeter (infinite internal resistance) is connected between points P and Q.
(a) What is the current in the loop?
(b) What does the voltmeter read? Answer:
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