How magnet can repeal grapes!
BY IKBAL AHMED
Materials Needed:
(1) Two large grapes, (2) drinking straw, (3) 2-foot (60-centimeter) length of string, (4) tape, (5) neodymium (rare-earth) magnets – a 1-inch (2-cm) cube works well; the bigger, the better, and (6) a stand to hang the grapes from-a ring stand works well, or you can make a stand using PVC.
Note on Magnets: Use neodymium magnets because they are very strong. Be careful with them, as they can pinch your skin if handled improperly.
Assembly:
1. Attach one end of the string to the middle of the straw using tape or by tying it.
2. Attach the other end of the string to your stand so that the straw can rotate freely, creating what’s called a torsional pendulum.
3. Slide a grape onto each end of the straw. You can make small cuts in the stem ends of the grapes to insert the straw ends into them. Adjust the position of the string and grapes to be balanced, but the straw doesn’t need to be completely horizontally levelled.
Instructions:
1. Hold one side of the magnet near a grape without touching it. You’ll see the grape move away from the magnet.
2. Remove the magnet and let the grape stop moving.
3. Flip the magnet over and hold the other side near the grape. Again, the grape will move away. This shows diamagnetism in action.
Explanation:
Diamagnetic materials, like grapes, are repelled by both poles of a magnet. This happens because, in diamagnetic materials, all the electrons are paired with electrons of opposite spin. Examples of such materials include helium, graphite, and water (which is abundant in grapes).
When you bring the magnet close to the grape, it induces an electric current in the atoms of the grape, making them magnetic in a way that repels the magnet. This phenomenon is predicted by Lenz’s law, which states that moving a magnet towards an electrical conductor creates electric currents in the conductor, turning it into an electromagnet that repels the magnet.
Diamagnetic repulsion is very weak compared to other types of magnetism. We can only easily demonstrate this weak force with the invention of strong rare-earth magnets.
Further Exploration:
To observe their magnetic properties, you can try mounting other objects, such as Aluminium, wood, or prunes, on the torsional pendulum.
There are three types of magnetism: ferromagnetism, diamagnetism, and paramagnetism. Iron is ferromagnetic and is attracted to both poles of a magnet. This attraction happens because, in atoms of iron, cobalt, and nickel, the spins of electrons align with electrons in neighbouring atoms, creating strong magnetization regions called domains.
Paramagnetic materials, like Aluminium and liquid oxygen, have single, unpaired electrons in their atoms or molecules. When exposed to a magnetic field, these electrons orient themselves, causing weak attraction to both magnetic poles.
Every electron behaves like a magnet because it carries charge and spins. Additionally, an electron in orbit around an atom can act as an electric current, turning it into an electromagnet.
Understanding the behaviour of ferromagnetic, diamagnetic, and paramagnetic materials fully requires studying quantum mechanics.
More about Neodymium magnets:
Neodymium magnets, also known as NdFeB or NIB magnets, are the strongest type of permanent magnets available today. They are made from an alloy of neodymium, iron, and boron, and belong to the family of rare-earth magnets. Here’s a detailed look at what makes them so powerful, their strength levels, and how they compare to everyday household magnets:
Why Neodymium Magnets Are So Strong
1. Atomic Structure: Neodymium magnets have a crystal structure that aligns all magnetic moments (spins of electrons) in the same direction. This alignment creates an exceptionally strong magnetic field.
2. Material Composition: The combination of neodymium, iron, and boron creates a powerful magnetic field. Neodymium (a rare-earth element) has unpaired electrons that contribute to its high magnetism.
3. High Magnetic Energy Density: Neodymium magnets have a high magnetic energy product (BHmax), typically in the range of 33 to 52 MGOe (Mega Gauss Oersteds). This means they store and deliver a large amount of magnetic energy in a small volume.
Strength of Neodymium Magnets in Units
Magnetic Field Strength: The magnetic field strength of neodymium magnets can reach up to 1.4 teslas (T). In comparison, the Earth’s magnetic field is about 50 microteslas (0.00005 T).
Pull Force: Neodymium magnets have a very strong pull force. For example, a small 1-inch diameter neodymium disc magnet can have a pull force of over 10 kg (22 pounds).
Comparison with Household Magnets
1. Refrigerator Magnets: The typical fridge magnet has a field strength of around 5 to 10 milliteslas (mT). In contrast, neodymium magnets are 100 to 200 times stronger.
2. Ceramic Magnets (Ferrite): Commonly used in speakers and school projects, these have a strength of around 0.3 teslas (T). Neodymium magnets are roughly 4 to 5 times stronger.
3. Alnico Magnets: Found in older electronics and some musical instruments, these have a strength of around 0.01 to 0.1 teslas (T). Neodymium magnets are significantly more powerful.
Applications and Safety Considerations
1. Neodymium magnets are used in high-tech applications like electric motors, headphones, MRI machines, and magnetic fasteners.
2. Due to their strength, they can be hazardous if not handled properly. Large neodymium magnets can cause serious injuries if body parts get trapped between them.
Further Reading:
For more information, you can read “Electricity and Magnetism: Berkeley Physics Course, Volume 2” by Edward M. Purcell, published in 1984 by McGraw-Hill.