Electric & Magnetic Fields

Yes. Gravity, magnetic interactions, and the interactions between electrically charged objects are all examples of objects exerting a force (push or pull) on each other without touching.

Some, but not all, metals will interact with magnets. Iron is the most common metal that is attracted by magnets. Some other common metals—copper, aluminum, and silver—are not attracted by magnets.

While students are likely to simply describe the interactions between like and opposite magnetic poles, a better explanation is that magnets produce fields that can attract or repel magnetic objects, including other magnets. These fields exist in an area around the magnet and can act on objects that are not touching the magnet.

When two materials rub together, negatively charged electrons can be transferred from one to the other. The material that loses electrons becomes positively charged, and the material that gains electrons becomes negatively charged. These opposite charges are attracted to each other, which causes the articles of clothing to stick together.

The needle of a compass is a small magnet that responds to the Earth’s magnetic field. The Earth’s magnetic field shifts over long timespans, and Earth’s current geographic North Pole is actually associated with its south magnetic pole. So the north pole of a compass needle will point toward the Earth’s geographic North Pole.

Magnetic fields can travel through solids, liquids, gases, and through a vacuum. So magnets can work under water and in space.

Magnetic forces get stronger as the magnet moves closer to the object it is attracting or repelling. If two magnets are made of the same material, then the larger magnet will have a stronger magnetic field. The strength of a magnet also depends on the material from which it is made. For example, neodymium magnets will have a stronger magnetic field than magnets made from Alnico (an alloy of aluminum, nickel, and cobalt).

Each tiny piece of iron becomes magnetized, and its poles align with the lines of the magnetic field. Therefore, the iron filings will line up to show the field lines and can be used to determine the relative strength of the field. Closely packed lines indicate a stronger field; widely spaced lines indicate a weaker field.

Balloons that have been rubbed with the same material will take on the same charge. Charged objects are surrounded by electric fields that can exert a force on other charged objects. Two balloons with the same charge will repel each other.

When the current is switched on, the coil is magnetized and attracts the metal projectile causing it to move down the barrel. If the current remained on, the projectile would move to the coil and then stop. Turning off the coil allows the projectile to continue travelling down and out of the barrel.

The video shows two factors that can increase the strength of an electromagnet: increasing the current passing through the wire coil and increasing the number of wire turns in the coil. Another factor that can increase the strength of an electromagnet is adding a metal core. Iron cores are the most common, but neodymium cores make the strongest electromagnets.

Opposite charges attract, and the toner particles attract to the paper. So the surface of the paper must have a positive charge.