21.A long, straight wire allows 3.50 A through it. What is the magnitude of the magnetic field 25.0 cm from the wire? Express the answer in microTesla (pT). Write magnitude only, unit is already given. A.

A transmission line strung 7.0 m above the ground carries a current of 500 A. What is the magnetic field on the ground directly below the wire? Compare your' answer with the magnetic field of Earth.

(a) A DC power line for a light-rail system carries 1000 A at an angle of 30.0° to the Earth’s 5.00105-T field. What is the force on a 100-m section of this line? (b) Discuss practical concerns this presents, if any.

The Earths Van Allen belts (Fig. 30.34) are a natural magnetic bottle, trapping cosmic rays that spiral back and forth between the North and South Poles. Use the shape of a cosmic rays path to describe the variation in the magnetic field strength.

(a) What is the speed of a supersonic aircraft with a 17.0-m wingspan, if it experiences a 1.60V Hall voltage between its wing lips when in level flight over the north magnetic pole, where the Earth's field strength is 8.00105T ? (b) Explain why very little current flows as a result of this Hall voltage.

A 25-cm nod moves at 5.0 m/s in a plane perpendicular to a magnetic field of strength 0.25 T. The rod, velocity vector, and magnetic field vector are mutually perpendicular, as indicated in tire accompanying figure. Calculate (a) the magnetic force on an electron in tire rod, (b) the electric field in the rod, and (c) the potential difference between the ends of the rod. (d) What is the speed of the rod if the potential difference is 1.0 V?

Is the Earth's magnetic field parallel to the ground at all locations? If not, where is it parallel to the surface? Is its strength the same at all locations? If not, where is it greatest?

Unreasonable results To construct a non-mechanical water meter, a 0.500-T magnetic field is placed across the supply water pipe to a home and the Hall voltage is recorded, (a) Find the flow rate through a 3.00-cm-diameter pipe if the Hall voltage is 60.0 mV. (b) What would the Hail voltage be for the same flow rate through a 10,0-cm- diameter pipe with tire same field applied?

A current of 1.2 A is flowing in a coaxial cable whose outer radius is five times its inner radius. What is the magnetic field energy stored in a 3.0-m length of the cable?

Certain experiments must be performed in the absence of any magnetic fields. Suppose such an experiment is located at the center of a large solenoid oriented so that a current of I = 1.00 A produces a magnetic field that exactly cancels Earths 3.50 105 T magnetic field. Find the solenoids number of turns per meter.