28. Magnetic Fields and Forces

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?

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?

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?

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?

Which of the following best explains why paperclips are attracted to magnets?

Which of the following materials or objects have scientists successfully levitated using very strong magnetic fields due to their diamagnetic properties?

A rectangular loop of wire is placed near a stationary bar magnet. If the magnet is held stationary and a current is suddenly established in the loop, in which direction does the loop swing relative to the magnet?

Which of the following best describes the direction of the magnetic force on a straight current-carrying wire placed perpendicular to a uniform magnetic field ($B$)?

A straight, 2.5 m wire carries a typical household current of 1.5 A (in one direction) at a location where the earth's magnetic field is 0.55 gauss from south to north. Find the magnitude and direction of the force that our planet's magnetic field exerts on this wire if it is oriented so that the current in it is running (a) from west to east, (b) vertically upward, (c) from north to south. (d) Is the magnetic force ever large enough to cause significant effects under normal household conditions?