28. Magnetic Fields and Forces

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?

When a charge moves near a magnetic field, what type of force does it experience?

Using the left-hand rule for generators, the center finger indicates the direction of the $\mathrm{what}$?

Given a straight wire carrying current $I$ placed in a uniform magnetic field $B$, which rule is used to determine the direction of the magnetic force acting on the wire?

Which of the following actions will increase the strength of the magnetic force exerted on a paper clip by a current-carrying wire?

If a magnet is held stationary next to a current-carrying wire, can a current be induced in the wire by the magnet's presence alone?

A straight wire carrying a current ($I$) is placed perpendicular to a uniform magnetic field ($B$) pointing into the page. What is the direction of the magnetic force ($F$) acting on the wire?

A 5-m current-carrying wire (red line) is ran through a 4 T magnetic field (blue lines), as shown. The angle shown is 30°. What must the magnitude and direction of the current in the wire be when it feels a 3 N force directed into the page?

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?

A thin, 50.0 cm long metal bar with mass 750 g rests on, but is not attached to, two metallic supports in a uniform 0.450 T magnetic field, as shown in Fig. E27.37. A battery and a 25.0 Ω resistor in series are connected to the supports. (a) What is the highest voltage the battery can have without breaking the circuit at the supports? (b) The battery voltage has the maximum value calculated in part (a). If the resistor suddenly gets partially short-circuited, decreasing its resistance to 2.00 Ω, find the initial acceleration of the bar.

A long wire carrying 4.50 A of current makes two 90° bends, as shown in Fig. E27.35. The bent part of the wire passes through a uniform 0.240 T magnetic field directed as shown in the figure and confined to a limited region of space. Find the magnitude and direction of the force that the magnetic field exerts on the wire.