Page 351 - ABCTE Study Guide_Neat

Previously Covered

In the previous section, we covered velocity and speed (and the differences between the two). Our review
also discussed Newton’s first law and the qualities of pressure.

Electricity and magnetism are interrelated concepts. Wrap a wire around a nail and connect the wire to a
battery. The nail will be able to pick up small metal objects because it has become an electromagnet. The
moving electric charges making up the electric current cause a magnetic field. Magnetic fields are
caused by moving charges or some other change in the electric forces. In a bar magnet, the electrons in
the iron atoms tend to orbit in the same direction, causing net electric currents in the piece of iron. Electric
currents in earth's molten-iron core create the earth's magnetic field, which is similar to the magnetic field
of a giant bar magnet.

In a similar way, a changing magnetic field can cause an electric current. Electric generators use this
principle to generate electricity. A rotating turbine in a magnetic field will feel the changing magnetic field
and produce an electric current.

Just as there are two types of electric charges (positive and negative), there are two types of magnetic
poles (north and south). The difference is that the two types of charges can exist in isolation, but north
and south magnetic poles must always come in pairs. The rule that like charges repel and unlike charges
attract also applies to magnetic poles.

Question

You have two bar magnets. The magnets are laid end to end in such a way that the two ends are
attracted to each other. What will happen if you turn one magnet around but not the other?

A The ends will still stick together because magnets always attract each other.

B The ends will still stick together because one of the magnets is a north pole and the
other is a south pole.

C The ends will repel because you are trying to bring like poles together.

D The ends will repel because both magnets have become either north
(or south) poles.

Answer

The correct answer is C. All magnets have both a north and a south pole. Magnets that are either north
poles only or south poles only do not exist. If the ends of the magnets in contact with each other attracted,
they were opposite poles. Turning one of the magnets around brings like poles into contact, so they will
repel each other.

What Are the Basic Types of Circuits?

In order for an electric current to flow, there must be a complete circuit. For a battery to light a bulb, the
wires must connect from the battery to the bulb and then from the bulb to the other terminal of the battery.

This type of circuit is called a series circuit. If two bulbs are connected in series, the wire goes from the
battery to one bulb, then to the other bulb, and finally back to the battery.