### Test: ACT Science

Magnets and electric charges show certain similarities. For example, both magnets and electric charges can exert a force on their surroundings. This force, when produced by a magnet, is called a magnetic field. When it is produced by an electric charge, the force is called an electric field. It has been observed that the strength of both magnetic fields and electric fields is inversely proportional to the square of the distance between a magnet or an electric charge and the objects that they affect.

Below, three scientists debate the relationship between electricity and magnetism.

Scientist 1:

Electricity and magnetism are two different phenomena. Materials such as iron, cobalt, and nickel contain magnetic domains: tiny regions of magnetism, each with two poles. Normally, the domains have a random orientation and are not aligned, so the magnetism of some domains cancels out that of other domains; however, in magnets, domains line up in the same direction, creating the two poles of the magnet and causing magnetic behavior.

In contrast, electricity is a moving electric charge which is caused by the flow of electrons through a material. Electrons flow through a material from a region of higher potential (more negative charge) to a region of lower potential (more positive charge). We can measure this flow of electrons as current, which refers to the amount of charge transferred over a period of time.

Scientist 2:

Electricity and magnetism are similar phenomena; however, one cannot be reduced to the other. Electricity involves two types of charges: positive and negative charge. Though electricity can occur in a moving form (in the form of current, or an electric charge moving through a wire), it can also occur in a static form. Static electricity involves no moving charge. Instead, objects can have a net excess of positive charge or a net excess of negative charge—because of having lost or gained electrons, respectively. When two static positive electric charges or two static negative electric charges are brought close together, they repel each other. However, when a positive and a negative static charge are brought together, they attract each other.

Similarly, all magnets have two poles. Magnetic poles that are alike repel each other, while dissimilar magnetic poles attract each other. Magnets and static electric charges are alike in that they both show attraction and repulsion in similar circumstances. However, while isolated static electric charges occur in nature, there are no single, isolated magnetic poles. All magnets have two poles, which cannot be dissociated from each other.

Scientist 3:

Electricity and magnetism are two aspects of the same phenomenon. A moving flow of electrons creates a magnetic field around it. Thus, wherever an electric current exists, a magnetic field will also exist. The magnetic field created by an electric current is perpendicular to the electric current's direction of flow.

Additionally, a magnetic field can induce an electric current. This can happen when a wire is moved across a magnetic field, or when a magnetic field is moved near a conductive wire. Because magnetic fields can produce electric fields and electric fields can produce magnetic fields, we can understand electricity and magnetism as parts of one phenomenon: electromagnetism.

 1 In an experiment, an iron bar that showed no magnetism was heated and allowed to cool while aligned North-South with the Earth's magnetic field. After it cooled, the iron bar was found to be magnetic. Scientist 1 would most likely explain this result by saying which of the following?

Interference occurred between the electric field of the bar and the magnetic field of the Earth, causing the bar to become magnetic.

The experiment induced an electric current in the bar, causing the bar to become magnetic.

The experiment caused the two magnetic poles of the bar to move so that they were aligned with the Earth's magnetic field.

The experiment caused the magnetic domains of the bar to move out of alignment with each other.

The experiment allowed the magnetic domains of the bar to line up, causing the bar to become magnetic.

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