Problem 4: Displacement currents. A planar capacitor has two circular plates with equal radii R separated by a distance h. A dielectric cylinder of a smaller radius r < R is inserted co-axially into the center of the capacitor. The dielectric permittivity of the cylinder is €. The voltage between the plates is linearly increased according to V = at. (a) Calculate the magnetic field at the edge of the cylinder. (b) Calculate the magnetic field at the edge of the capacitor. V h حمد

Problem 4: Displacement currents. A planar capacitor has two circular plates with equal radii R separated by a distance h. A dielectric cylinder of a smaller radius r < R is inserted co-axially into the center of the capacitor. The dielectric permittivity of the cylinder is €. The voltage between the plates is linearly increased according to V = at. (a) Calculate the magnetic field at the edge of the cylinder. (b) Calculate the magnetic field at the edge of the capacitor. V h حمد

Principles of Physics: A Calculus-Based Text

5th Edition

ISBN:9781133104261

Author:Raymond A. Serway, John W. Jewett

Publisher:Raymond A. Serway, John W. Jewett

Chapter24: Electromagnetic Waves

Section: Chapter Questions

Problem 2P

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A strip of copper is placed in a uniform magnetic field of magnitude 2.5 T. The Hall electric field is measured to be 1.5103V/m (a) What is the drift speed of the conduction electrons? (b) Assuming that n =8.01028 elections per cubic meter and that the cross-sectional area of the strip is 5.0106m2 , calculate the current in the ship, (c) What is the Hall coefficient 1/nq?
A long, straight wire of radius R caries a current I that is distributed uniformly over the cross-section of the wire. At what distance from the axis of the wire is the magnitude of the magnetic field a maximum?
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A long, straight, cylindrical conductor contains a cylindrical cavity whose axis is displaced by n from the axis of the conductor, as shown in the accompanying figure. The current density in the conductor is given by J=J0k, where J0 is a constant and k is along the axis of the conductor. Calculate the magnetic field at an arbitrary point P in the cavity by superimposing the field of a solid cylindrical conductor with radius R1and current density Jonto the field of a solid cylindrical conductor with radius R2and current density J . Then use the fact that the appropriate azimuthal unit vectors can be expressed as 1=kr1and 2=kr2 to show that everywhere inside the cavity the magnetic field is given by the constant B=120J0ka , where a=r1r2 and r1=r1r1 is the position of P relative to the center of the conductor and r2=r2r2 is the position of P relative to the center of the cavity.
A parallel-plate capacitor with plate separation d is connected to a source of emf that places a time-dependent voltage V(t) across its circular plates of radius r0and area (a) Write an expression for the time rate of change of energy inside the capacitor in terms of V(t) and dV(t)/ dt. (b) Assuming that V(t) is increasing with time, identify the directions of the elecuic field lines inside the capacitor and of the magnetic field lines at the edge of the region between the plates, and then the direction of the Poynting vector S at this location. (c) Obtain expressions for the time dependence of E(t), for B(t) from the displacement current, and for the magnitude of the Poynting vector at the edge of the region between the plates. (d) From S , obtain an expression In terms of ‘(t) and dV(t)/dt for the rate at which electromagnetic field energy the region between the plates. (e) Compare the results of pails (a) and (d) and explain the relationship between them.
A toroid has a major radius R and a minor radius r and is tightly wound with N turns of wire on a hollow cardboard torus. Figure P31.6 shows half of this toroid, allowing us to see its cross section. If R r, the magnetic field in the region enclosed by the wire is essentially the same as the magnetic field of a solenoid that has been bent into a large circle of radius R. Modeling the field as the uniform field of a long solenoid, show that the inductance of such a toroid is approximately L=120N2r2R Figure P31.6
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A proton precesses with a frequency p in the presence of a magnetic field. If the intensity of the magnetic field is doubled, what happens to the precessional frequency?
The Hall effect finds important application in the electronics industry. It is used to find the sign and density of the carriers of electric current in semiconductor chips. The arrangement is shown in Figure P22.66. A semiconducting block of thickness t and width d carries a current I in the x direction. A uniform magnetic field B is applied in the y direction. If the charge carriers are positive, the magnetic force deflects them in the z direction. Positive charge accumulates on the top surface of the sample and negative charge on the bottom surface, creating a downward electric field. In equilibrium, the downward electric force on the charge carriers balances the upward magnetic force and the carriers move through the sample without deflection. The Hall voltage ΔVH = Vc − Va between the top and bottom surfaces is measured, and the density of the charge carriers can be calculated from it. (a) Demonstrate that if the charge carriers are negative the Hall voltage will be negative. Hence, the Hall effect reveals the sign of the charge carriers, so the sample can be classified as p-type (with positive majority charge carriers) or n-type (with negative). (b) Determine the number of charge carriers per unit volume n in terms of I, t, B, ΔVH, and the magnitude q of the carrier charge. Figure P22.66
Suppose the parallel-plate capacitor shown below is accumulating charge at a rate of 0.010 C’s. What is the induced magnetic field at a distance of 10 cm from the capacitator?