Exam 29: Magnetic Fields Due to Currents

In the figure, the current element , the point P, and the three vectors (1, 2, 3)are all in the plane of the page.The direction of , due to this current element, at the point P is:

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:

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

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:

A hollow cylindrical conductor (inner radius = a, outer radius = b)carries a current i uniformly spread over its cross section.Which graph below correctly gives B as a function of the distance r from the center of the cylinder?

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 magnitude of the magnetic field at point P, at the center of the semicircle shown, is given by:

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

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

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:

Two long straight wires pierce the plane of the paper at vertices of an equilateral triangle as shown below.They each carry 2.0 A, out of the paper.The magnetic field at the third vertex (P)has magnitude:

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?

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

In Ampere's law, the symbol is:

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

Magnetic field lines inside the solenoid shown are:

Two long straight wires enter a room through a window.One carries a current of 3.0 A into the room while the other carries a current of 5.0 A out.The magnitude of the path integral around the window frame is:

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

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:

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