This week, begin electro-magnetic researches in the footsteps of Mr. James Marsh, of Rush-grove-place, Woolwich and Mr. W. Sturgeon, 8, Artillery-Place, Woolwich to construct a Portable Electro-Magnetic Apparatus
A magnet produces a magnetic field that can exert an attractive force on ferromagnetic metals like iron and steel. At room temperature, four elements are ferromagnetic: iron, cobalt, nickel, and gadolinium. Only ferromagnetic materials can become permanent magnets through various processes of magnetism.
The magnetic field is the result of the movement of an atom’s electrons. In most materials, the spin and orbit of the atoms that form the magnetic moments are pointing in random directions, so the burgeoning magnetic fields cancel out and do not produce a notable amount of magnetism. A ferromagnetic material contains aligned magnetic moments, so the magnetic field is parallel and can combine together to form a magnetic field. However, the alignment is limited to a region known as a domain, but ferromagnetic materials contain many domains. While domains form a magnetic field, they are typically randomly oriented, so most ferromagnetic materials found in nature do not normally contain magnetism.
There are three types of magnets: permanent, temporary, and natural. A permanent magnet is a magnet that is magnetized permanently and contains a persistent magnetic field. Lodestones are natural sources of magnetized materials and have been known since Earth’s antiquity by an endlessly large list of names including lightning stones or, most appropriately, magnetite. Magnetite is the raw material for steel and can become permanently magnetized when exposed to an external magnetic field. However, while magnetite behaves as a ferromagnetic metal, it is actually ferrimagnetic. Magnetite’s unique crystal structure forms two opposing but unequal polarities producing a net magnetic moment that forms its magnetic field. This is unlike ferromagnetic materials that rely on the sum of the magnetic moments of all the atoms in the material.
Magnets can come in many shapes, but each contain a magnetic north and south pole, located on opposing sides of the structure. Magnetic fields always form closed loops. To the naked eye, the magnetic field lines are invisible, but can be indirectly seen by placing a magnet in a field of iron shavings that will align parallel to the magnetic field.
Permanent magnets have the advantage that they can be found in nature and can therefore be readily used, however they also have a number of disadvantages. A permanent magnet can lose its natural magnetism in any number of ways. Most troubling while cold can strengthen magnets, heating a magnet to a high critical temperature can considerably weaken it. This is the metal’s Curie point, named after French physicist Pierre Curie in the 1800’s, and when it is reached, magnetism is eradicated. The Curie temperature for ferromagnetic materials varies (between 600-800 degrees C), where iron’s Curie point is around 700 C (1418 F) and Nickel is 354 C (669 F). Even when cooled, the magnetism remains permanently weakened. Also—possibly more common for a traveling chrononaut—sharp impacts like dropping a magnet can break and randomize its internal magnetic orientation, weakening it dramatically.
The third type of magnet—a temporary magnet—depends on a fundamental principle of electromagnetism. In electromagnetism, rather than treating magnetic fields and electric fields as separate, they are intimately connected.
It is more accurate to view magnetic and electric fields as both acting as chicken and egg. A moving magnetic field generates a current and a current generates a magnetic field. This underlying principle allows for the construction of a man-made electromagnet. A permanent magnet produces a perpetual magnetic field due to its natural properties, whereas an electromagnet is temporary since it requires a continual supply of current to form a magnetic field. However, the strength of the magnetic field can be adjusted and intensified with an increase in current and as a result often create a stronger magnetic field for the magnet’s size compared to its naturally occurring cousins.
A solenoid is a type of electromagnet created by inducing a magnetic field with current in a cylindrical coil of wire. When current is running through the wire, the closely aligned coils superimpose the magnetic field from each loop, strengthening each in turn. Solenoids can act in the same way as permanent magnets, attracting and repelling other magnets as well as attracting ferromagnetic materials like steel. The electromagnet is only a magnet as long as an electric current is flowing through the coil, allowing the magnet to be turned off and on, making it more flexible than its permanent counterpart.
The history of magnetism, and in particular, induced magnetic fields like the electromagnet, began at the very edge of the 19th century. Electromagnets require a constant current to produce a magnetic field. In 1799, Alessandro Volta demonstrated his invention of the voltaic pile, a type of battery. With this invention, physicists, chemists, and stranded chronouats had their first stable and cheap source of electric current.
Magnetism is produced by a moving electric charge, so as electrons are moved through a wire, the charged particle’s movement creates a magnetic field. In addition, a magnetic field can cause charged particles like electrons to move. The movement of charge from one region to another is known as current.
Hans Christian Ørsted demonstrated the interconnected relationship between current and magnetic fields in 1820, only a few years before British scientists James Marsh and William Sturgeon displayed the first electromagnets to an eager audience in 1824 and 1825, eventually improved upon by Joseph Henry in the years to follow. The first electromagnet displayed was built around a ferromagnetic iron horseshoe, crudely wrapped 18 times by bare copper wire, partially insulated by shellac, a natural resin used to finish wood. The first electromagnet was only 7 ounces (.5 kg) but was capable of lifting nearly 9 pounds (~4 kg). This early electromagnet was quickly surpassed within 10 years by an electromagnet capable of carrying over 3300 pounds
(~1500 kg) by Joseph Henry. Henry had quickly outperformed the original design by experimenting with variations on Sturgeon’s original design. Most importantly, by insulating the coiled wires from one another. By preventing current from passing between the coils of bare wire, he had the opportunity to wrap multiple layers of wire around the same core, exponentially increasing the electromagnet’s power.
Electromagnets require very few supplies and no complex tools to construct. Solenoids depend on two fundamental materials: a length of insulated wire and a continuous power source. Insulating the wire is vitally important as it prevents the flow of electricity from jumping between the adjacent
coils. The current is then forced to travel all the way through and around the coiled length of wire, increasing the strength of the produced magnetic field. Historically, before the invention of enameled wire, wires were insulated with resin and, in a pinch, even cloth with mixed results. When a wire is wrapped in a coil, each part of the wire containing current will produce a magnetic field, but in close proximity, the magnetic field lines will merge together to form a single larger and stronger magnetic field.
The magnetic field can be strengthened by increasing the current passing through the wire or by increasing the number of times the wire is coiled around the core. However, increasing the length of the solenoid will decrease its strength. In order to maximize the strength, a clever chrononaut can increase the number of coiled turns, but minimize the width of a solenoid, by stacking the coil into layers. However, it must be ensured that the layers are coiled in the same direction for each layer to avoid the magnetic fields of one layer cancelling out the fields of another.
Ampère's Law for Magnetic Strength β = Magnetic flux density* μ = magnetic constant = 4π×10−7 H/m or N/Amp2 N = number of turns I = current ℓ = length of solenoid
Finally, connect the two exposed ends of the wire to the source of current, most commonly a battery. Once current can flow through the wire a magnetic field will be generated. As long as the current is running uninterrupted, the electromagnet will behave functionally as a traditional permanent magnet. It will attract ferromagnetic materials, attract and repel other magnets, and contain a north and south pole.
The strength of the magnet can be calculated based on the strength of the magnetic field, which can be used to predict the weight that the magnet will be able to support.
The right hand rule is a simple way to determine the poles of a solenoid. The direction of the magnetic field (clockwise or counterclockwise) depends on the flow of the current.
The fingers in a fist are coiled in the direction of the coil (the direction of conventional current and in the opposite direction that the electrons are flowing) and the thumb represents the magnetic north pole of the magnet.
The force of the magnet (in Newtons) is based on the strength of the magnet, as well as the area and distance of the metal being attracted.
So, a solenoid with 120 turns and 10 Amperes** current will produce a magnetic strength of: (120 x 10)2 (4π×10−7) = 72π/125. If the piece of metal 0.5 meters away and a cross-section of the metal’s area is 1.5 meters, then the force of the electromagnet will be:
On a planet like Earth with a gravity of 9.8065 m/s2, Newtons can be converted to kilograms of force through Newton’s Second Law of Motion where F = ma, where:
So, this magnet will be producing 0.554 kilograms of force.
The strength can vary as the center of the coil contains the strongest and most compact magnetic field lines. Once the current stops flowing, the magnetism of the solenoid is turned off, but the metal core can still exhibit small amounts of residual magnetism.
Constructing an electromagnet is as simple as a wire and a stable current, and as complex as lots of wire and a stronger current