29. Sources of Magnetic Field

The toroid of FIGURE P29.54 is a coil of wire wrapped around a doughnut-shaped ring (a torus). Toroidal magnetic fields are used to confine fusion plasmas. Is a toroidal magnetic field a uniform field? Explain.

A 50 cm solenoid with 1000 turns has an inductance of 20 mH. What is the magnetic field strength inside the inductor when the current is 75 mA?

(II)A toroid (Fig. 28–17) has a 50.0-cm inner diameter and a 54.0-cm outer diameter. It carries a 25.0-A dc current in its 785 loops. Determine the range of values for B inside the toroid.

A toroid is fabricated with a circular shape and loops with a square cross section as shown in Fig. 28–69. The cross-section of a loop is a square of side 6.0 cm. The inner radius of the whole circular toroid is 3.0 m. There are 320 loops of wire which carry a 45-A dc current using a nearby power supply at 20.0 V. The arrows show the current flow in and out of the toroid. The current flows up at the inner diameter and down at the outer diameter. (a) Calculate the strength of the magnetic field at the center of the square’s cross section at point P. (b) Is the magnetic field pointing clockwise or counterclockwise? (c) The square cross-sectional area of the wire is uniformly 0.10 cm². What is the resistivity of the wire?