28. Magnetic Fields and Forces

The force on a wire carrying 6.45 A is a maximum of 1.64 N when placed between the pole faces of a magnet. If the pole faces are 55.5 cm in diameter, what is the approximate strength of the magnetic field?

The power cable for an electric trolley (Fig. 27–60) carries a horizontal current of 330 A toward the east. The Earth’s magnetic field has a strength 5.0 x 10^-5 T and makes an angle of dip of 22° at this location. Calculate the magnitude and direction of the magnetic force on a 15-m length of this cable.

A rectangular wire loop of length $L$ and width $w$ carries a current $I$ and is placed in a uniform magnetic field $B$ that is perpendicular to the plane of the loop. What is the magnitude of the net magnetic force acting on the loop?

Two long, parallel wires are separated by a distance $d$. The upper wire carries a current $i{1}_{}$ to the right, and the lower wire carries a current $i{2}_{}$ to the right. What should the value of $i{2}_{}$ be so that the net magnetic field at a point $p$ located exactly midway between the wires is zero?

When an electromagnet carrying current is placed in an external magnetic field, which of the following best describes the effect on the electromagnet?

A wire along the x-axis carries current I in the negative x-direction through the magnetic field . Find an expression for the net torque on the wire about the point x = 0.

Near the equator, the Earth’s magnetic field points almost horizontally to the north and has magnitude B = 0.50 x 10⁻⁴ T. What should be the magnitude and direction for the velocity of an electron if its weight is to be exactly balanced by the magnetic force?

A long straight wire carries a constant current to the right. Four rectangular loops (A, B, C, D) are positioned near the wire. Loop A moves parallel to the wire to the right, loop B moves parallel to the wire to the left, loop C moves directly away from the wire, and loop D moves directly toward the wire. Which loop will experience an induced current due to its motion relative to the wire?

Under what condition is the magnetic force on a straight current-carrying wire placed in a uniform magnetic field at its maximum value?

Which of the following situations will always produce a magnetic force on a nearby iron nail?

(II) A current-carrying circular loop of wire (radius r, current I) is partially immersed in a magnetic field of constant magnitude B₀ directed out of the page as shown in Fig. 27–43. Determine the net force on the loop due to the field in terms of θ₀. (Note that θ₀ points to the dashed line, above which B = 0.)

In a uniform magnetic field, a current-carrying wire experiences a force due to the interaction between the current and the magnetic field. Which type of charge carriers in the wire are deflected the most by the magnetic field?

A straight, vertical wire carries a current of 2.60 A downward in a region between the poles of a large superconducting electromagnet, where the magnetic field has magnitude B = 0.588 T and is horizontal. What are the magnitude and direction of the magnetic force on a 1.00 cm section of the wire that is in this uniform magnetic field, if the magnetic field direction is (a) east?

Which of the following best describes how electromagnets differ from permanent magnets?

Why is every piece of $\mathrm{Fe}$ not a magnet, even though $\mathrm{Fe}$ is a magnetic material?