A thin $10 \mathrm{~cm}$ long solenoid used for fast electromechanical switching has $400$ loops of wire and carries a current of $2.0 \mathrm{~A}$. Estimate the field inside near the center.

A rectangular loop of wire is placed next to a straight wire, as shown in the given figure. There is a current of 3.5 A in both wires. Determine the magnitude and direction of the net force on the loop.

Can an iron rod attract a magnet? Can a magnet attract an iron rod? What must you consider to answer these questions?

A compass needle points $13^{\circ} \mathrm{E}$ of $\mathrm{N}$ outdoors. However, when it is placed $16.0 \mathrm{~cm}$ to the east of a vertical wire inside a building, it points $55^{\circ} \mathrm{E}$ of $\mathrm{N}$. What is the magnitude and direction of the current in the wire? The Earth's field there is $0.50 \times 10^{-4} \mathrm{~T}$ and is horizontal.

An unmagnetized nail will not attract an unmagnetized paper clip. However, if one end of the nail is in contact with a magnet, the other end will attract a paper clip. Explain.

A dc power line carries a current of $85 \mathrm{~A}$ west along the tops of $8.5 \mathrm{~m}$ high poles. Where would the current's magnetic field cancel the Earth's field?

A dc power line carries a current of $85 \mathrm{~A}$ west along the tops of $8.5 \mathrm{~m}$ high poles. What is the magnitude and direction of the magnetic field produced by this wire at the ground directly below? How does this compare with the Earth's field of about $\frac{1}{2} \mathrm{G}$ ?

Will a magnet attract any metallic object, such as those made of aluminum or copper? (Try it and see.) Why is this so?

A third wire is placed in the plane of the two wires shown in the given figure parallel and just to the right. If it carries 25.0 A upward, what force per meter of length does it exert on each of the other two wires? Assume it is 2.8 mm from the nearest wire, center to center.

A heavy block of iron, at rest, is attracted by a heavy magnet. Before striking the magnet the block has acquired considerable kinetic energy. When the block strikes the magnet, some of the latter's domains may be jarred into randomness; describe the energy transformations.

A heavy block of iron, at rest, is attracted by a heavy magnet. Before striking the magnet the block has acquired considerable kinetic energy. What is the source of this kinetic energy?

A type of magnetic switch similar to a solenoid is a relay. A relay is an electromagnet (the iron rod inside the coil does not move) which, when activated, attracts a piece of iron on a pivot. Design a relay to close an electrical switch. A relay is used when you need to switch on a circuit carrying a very large current but you do not want that large current flowing through the main switch. For example, the starter switch of a car is connected to a relay so that the large current needed for the starter doesn't pass to the dashboard switch.

Two long straight wires each carry a current I out of the page toward the viewer. Indicate, with appropriate arrows, the direction of $\overrightarrow{\mathbf{B}}$ at each of the points 1 to 6 in the plane of the page. State if the field is zero at any of the points.

How might you measure the magnetic dipole moment of the Earth?