Exam 29: Magnetic Fields Due to Currents

A long straight cylindrical shell has an inner radius R_i and an outer radius R_o.It carries a current i, uniformly distributed over its cross section.A wire is parallel to the cylinder axis, in the hollow region (r < R_i).The magnetic field is zero everywhere outside the shell (r > R_o).We conclude that the wire:

The diagram shows three equally spaced wires that are perpendicular to the page.The currents are all equal, two being out of the page and one being into the page.Rank the wires according to the magnitudes of the magnetic forces on them, from least to greatest.

A toroid has a square cross section with the length of an edge equal to the radius of the inner surface.The ratio of the magnitude of the magnetic field at the inner surface to the magnitude of the field at the outer surface is:

The magnetic field inside a long ideal solenoid is independent of:

A solenoid is 3.0 cm long and has a radius of 0.50 cm.It is wrapped with 500 turns of wire carrying a current of 2.0 A.The magnetic field at the center of the solenoid is:

The magnetic field a distance 2 cm from a long straight current-carrying wire is 2 * 10^-5 T.The current in the wire is:

Two parallel wires, 4 cm apart, carry currents of 2 A and 4 A respectively, in opposite directions.The force per unit length of one wire on the other is:

An ordinary magnetic compass is placed flat on the ground.A wire carrying a large current i from east to west is placed directly above the compass.The end of the compass needle marked "N" will point:

A square loop of current-carrying wire with edge length a is in the xy plane, the origin being at its center.Along which of the following lines can a charge move without experiencing a magnetic force?

Two parallel wires, 4 cm apart, carry currents of 2 A and 4 A respectively, in the same direction.The force per unit length of one wire on the other is:

A constant current is sent through a helical coil made of flexible wire.The coil:

In the figure, there are three wires carrying currents in the indicated directions, and an Amperian loop.The sign of the contribution of the current in each wire to the path integral in Ampere's Law is:

Magnetic field lines inside the solenoid shown are:

A 45-m long wire is coiled so that it makes a coil containing 100 circular loops, one on top of the other.If the wire carries a current of 13 A, what is the magnetic dipole moment of the coil?

A long straight cylindrical shell carries current i uniformly distributed over its cross section.The magnitude of the magnetic field is greatest:

Two long ideal solenoids (with radii 20 mm and 30 mm respectively)have the same number of turns of wire per unit length.The smaller solenoid is mounted inside the larger, along a common axis.It is observed that there is zero magnetic field within the inner solenoid.The current in the inner solenoid must be:

Which graph correctly gives the magnitude of the magnetic field outside an infinitely long, very thin, straight current-carrying wire as a function of the distance r from the wire?

Two long straight wires are parallel and carry current in opposite directions.The currents are 8.0 A and 12 A and the wires are separated by 0.40 cm.The magnetic field at a point midway between the wires is:

If R is the distance from a magnetic dipole, then the magnetic field it produces is proportional to:

A coulomb is: