Exam 29: Magnetic Fields Due to Currents

The diagram shows three arrangements of circular loops, centered on vertical axes and carrying identical currents in the directions indicated. Rank the arrangements according to the magnitudes of the magnetic fields at the midpoints between the loops on the central axes.

Two parallel wires carrying equal currents of 10 A attract each other with a force of 1 mN. If both currents are doubled, the force of attraction will be:

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

In Ampere's law, the direction of the integration around the path:

The magnetic field outside a long straight current-carrying wire depends on the distance R from the wire axis according to:

Magnetic field lines inside the solenoid shown are:

The diagrams show three circuits consisting of concentric circular arcs (either half or quarter circles of radii r, 2r, and 3r) and radial lengths. The circuits carry the same current. Rank them according to the magnitudes of the magnetic fields they produce at C, least to greatest.

In Ampere's law, the integration must be over any:

Two long straight wires pierce the plane of the paper at vertices of an equilateral triangle as shown below. They each carry 2 A, out of the paper. The magnetic field at the third vertex (P) has magnitude (in T):

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

A long straight wire carrying a 3.0 A current enters a room through a window 1.5 m high and 1.0 m wide. The path integral around the window frame has the value (in T.m):

Four long straight wires carry equal currents into the page as shown. The magnetic force exerted on wire F is:

In an overhead straight wire, the current is north. The magnetic field due to this current, at our point of observation, is:

Suitable units for $\mu$ ₀ are:

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

Two parallel long wires carry the same current and repel each other with a force F per unit length. If both these currents are doubled and the wire separation tripled, the force per unit length becomes:

Lines of the magnetic field produced by a long straight wire carrying a current are:

Electrons are going around a circle in a counterclockwise direction as shown. At the center of the circle they produce a magnetic field that is:

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

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 in the hollow region. We conclude that the wire: