Exam 24: Magnetic Fields and Forces

In order to trap the starship Enterprise, the diabolical Klingons build a huge ideal solenoid 10 light-years long with a diameter of 2.0 million kilometers. Every kilometer of length of the solenoid contains 100 turns of wire. What magnetic field strength is produced near the center of the solenoid using a current of 2.00 kA? (μ₀ = 4π × 10^-7 T ∙ m/A)

A wire in the shape of an "M" lies in the plane of the paper. It carries a current of 2.0 A, flowing from A to E, as shown in the figure. It is placed in a uniform magnetic field of 0.85 T in the same plane, directed as shown on the right side of the figure. The figure indicates the dimensions of the wire. Note that AB is parallel to DE and to the baseline from which the magnetic field direction is measured. What are the magnitude and direction of the force acting on section DE of this wire?

A charged particle is injected into a uniform magnetic field such that its velocity vector is perpendicular to the magnetic field lines. Ignoring the particle's weight, the particle will

When the switch is closed in the circuit shown in the figure, the wire between the poles of the horseshoe magnet deflects upward. From this you can conclude that the left end of the magnet is

A long straight wire on the z-axis carries a current of 8.0 A in the +z direction (out of the paper). A circular loop of radius 10 cm lies in the xy-plane and carries a 3.0-A current, as shown in the figure. Point P, at the center of the loop, is 25 cm from the z-axis. An electron is projected from P with a velocity of 3.0 × 10⁶ m/s in the -x direction. What is the y component of the magnetic force on the electron? (e = 1.60 × 10^-19, μ₀ = 4π × 10^-7 T ∙ m/A)

When two long parallel wires carry unequal currents, the magnitude of the magnetic force that one wire exerts on the other is F. If the current in both wires is now doubled, what is the magnitude of the new magnetic force on each wire?

A flat circular wire loop of area 0.25 m² carries a current of 5.0 A. This coil lies on a horizontal table with the current flowing in the counterclockwise direction when viewed from above. At this point, the earth's magnetic field is 1.2 × 10^-5 T directed 60° below the horizontal. What is the magnitude of the torque that the earth's magnetic field exerts on this loop?

A straight bar magnet is initially 4 cm long, with the north pole on the right and the south pole on the left. If you cut the magnet in half, the right half will

A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure. If there is a current I flowing through this coil in the direction shown, what is the direction of the force acting on section CD of this coil?

A flat rectangular loop of wire is placed between the poles of a magnet, as shown in the figure. It has dimensions w = 0.60 m and L = 1.0 m, and carries a current I = 2.0 A in the direction shown. The magnetic field due to the magnet is uniform and of magnitude 0.80 T. The loop rotates in the magnetic field and at one point the plane of the loop is perpendicular to the field. At that instant, what is the magnitude of the torque acting on the wire due to the magnetic field?

If a calculated quantity has units of $\frac { \mathrm { N } \cdot \mathrm { s } } { \mathrm { C } \cdot \mathrm { m } }$ , that quantity could be

A vertical wire carries a current vertically downward. To the east of this wire, the magnetic field points

We observe that a moving charged particle experiences no magnetic force. From this we can definitely conclude that

A thin copper rod 1.0 m long has a mass of 0.050 kg and is in a magnetic field of 0.10 T. What minimum current in the rod is needed in order for the magnetic force to balance the weight of the rod?

An electron moving along the +x-axis enters a magnetic field. If the electron experiences a magnetic deflection in the -y direction, then the magnetic field must have a component

A vertical wire carries a current straight up in a region where the magnetic field vector points toward the north. What is the direction of the magnetic force on this wire?

A wire lying in the plane of the page carries a current toward the bottom of the page, as shown in the figure. What is the direction of the magnetic force it produces on an electron that is moving to the left directly toward the wire, as shown?

When a ferromagnetic material is placed in an external magnetic field, the net magnetic field of its magnetic domains becomes

Consider two current-carrying circular loops. Both are made from one strand of wire and both carry the same current, but one has twice the radius of the other. If the magnetic field strength at the center of the smaller loop is B, what is the magnetic field strength at the center of the larger loop?

A flat rectangular loop of wire is placed between the poles of a magnet, as shown in the figure. It has dimensions w = 0.60 m and L = 1.0 m, and carries a current I = 2.0 A in the direction shown. The magnetic field due to the magnet is uniform and of magnitude 0.80 T. The loop rotates in the magnetic field and at one point the plane of the loop makes a 30° angle with the field. At that instant, what is the magnitude of the torque acting on the wire due to the magnetic field?