Magnetic Grapes (Lourdes Ramos Quevedo)

Lourdes Ramos Quevedo

Principle(s) Illustrated

1. Magnetism

2. Diamagnetism

3. Properties of water

Standards

• 1.1.1 - Science Standard

• 1.1.2 - Science Standard

• 1.1.3 - Science Standard

Questioning Script

Prior knowledge & experience:

Students are familiar with magnets and how they work.

Students know that similar charged particles repel each other & oppositely charged particles attract.

Students are familiar with grapes.

Root question:

Why are grapes magnetic?

Target response:

Grapes are not magnetic. They contain water molecules which are diamagnetic.

Common Misconceptions:

• Kids may end up believing that grapes are magnetic.

• Iron is the only type of metal with magnetic properties.

Background Information:

Ferromagnetic materials, such as iron, are strongly attracted to both poles of a magnet.

Paramagnetic materials, such as aluminum, are weakly attracted to both poles of a magnet.

Diamagnetic materials, however, are repelled by both poles of a magnet. The diamagnetic force of repulsion is very weak (a hundred thousand times weaker than the ferromagnetic force of attraction). Water, the main component of grapes, is diamagnetic.

When an electric charge moves, a magnetic field is created. Every electron is therefore a very tiny magnet, because electrons carry charge and they spin. Additionally, the motion of an orbital electron is an electric current, with an accompanying magnetic field.

In atoms of iron, cobalt, and nickel, electrons in one atom will align with electrons in neighboring atoms, making regions called domains, with very strong magnetization. These materials are ferromagnetic, and are strongly attracted to magnetic poles.

Atoms and molecules that have single, unpaired electrons are paramagnetic. Electrons in these materials orient in a magnetic field so that they will be weakly attracted to magnetic poles. Hydrogen, lithium, and liquid oxygen are examples of paramagnetic substances.

Atoms and molecules in which all of the electrons are paired with electrons of opposite spin, and in which the orbital currents are zero, are diamagnetic. Helium, bismuth, and water are examples of diamagnetic substances.

If a magnet is brought toward a diamagnetic material, it will generate orbital electric currents in the atoms and molecules of the material. The magnetic fields associated with these orbital currents will be oriented such that they repelled by the approaching magnet.

This behavior is predicted by a law of physics known as Lenz's Law. This law states that when a current is induced by a change in magnetic field (the orbital currents in the grape created by the magnet approaching the grape), the magnetic field produced by the induced current will oppose the change.

Photographs and Movies