Learning about magnetic fields

Yurivani Rodriguez Olmeda

In this article we are going to talk about magnetic fields. Magnetic fields are surrounding you and you can’t see them. But they are here with a function, and here you are going to learn about them. First, let’s talk about the beginning of magnetic fields. The Greeks where the first people in discover the magnets. They found them in a region of Asia named as Magnesia. Oersted was the man who discovered that a current produce a magnetic field. There are some materials that have big magnetic properties. Some of them are nickel, iron and cobalt. Those are met as magnets too. In physics we study more profound the magnetic field. It is a region in the space in which an electric charge q is displaced in a velocity v, it suffers the effects of a perpendicular force that is perpendicular and proportional to the velocity as the field, and this force is named magnetic induction.( (F ) ⃗=q(v ) ⃗x B ⃗) A fundamental law that permits us to calculate the magnitude of the magnetic field is the Law of Amper. This law calculates the magnetic field produced by a distribution of currents when they have symmetry and time doesn’t change.∮▒□(→┬(B )• □(→┬dl )= μ˳I). There the first term refers to circulation of magnetic field around a close trajectory and the second member, the term I, is referred to the intensity that crosses a way and the last one, the μ˳ is the magnetic constant of permeability. The length cut in small pieces is equal to:∫▒〖dl=2πr〗If we substitute the equation to find the magnetic field according with the law of Amper, we get:

B(2πr)= μ˳I

B=(μ˳I)/((2πr) )

I don’t know if hear about solenoids. Solenoids are coiled wired in form of prop or spirals where circulate an electric current. When this happened a magnetic field is generated in the solenoid. The lines of the field inside the solenoid are almost parallel distribute uniformly or constant. This indicates that the field inside the solenoid is constant. We can use the law of Ampere to get an expression for the magnetic field inside the solenoid.

∮▒〖B*dl=B* ∮▒dl〗=Bl

The law of Ampere involves a total current passing through the closed area.

∮▒〖B dl=Bl= μ˳NI〗

B= μ˳N/l I= μ˳nI

There n= N/l means the number of laps in units of length. Where n= N/l means the number of turns. Solenoids are important because they can create controlled magnetic fields and can be used as electromagnets.

Another theme about magnetic fields that we have to learn are dipoles. A dipole is a source of magnetic field, with a south pole and a North Pole. The Earth is an example of a dipole. Since opposite ends of magnets are attracted, the north pole of a magnet is attracted to the south pole of another magnet. The Earth's North Magnetic Pole (currently in the Arctic Ocean, north of Canada) is physically a south pole, as it attracts the north pole of a compass. Every magnet as a North and South pole. Michael Faraday created imaginary lines to explain the behavior of the force in the magnetic fields. Those imaginary lines leave the North pole and enters in the South pole. They don’t finish and neither cross each other because they are close. At any point the direction of the magnetic field vector is tangent. In this image we can see the behavior of the imaginary lines of our North and South poles. As you can see our South pole is uprith and the North pole is downward.

We are going to finish this article talking about another theme related with magnetic field is named the law of Faraday. This law was established by Michael Faraday at 1831. There he established that an induced voltage in a closed circuit is directly proportional to the speed at what does the time changes and the magnetic flux that crosses a surface. The emf induce in a circuit equals the rate of change of the magnetic field. In the experiments that these great man realized they conclude that we can induce an emf using a simple wile coil inside a magnetic field. More simple to understand we shall see the equation that describe this meaning that is: ∈=-N dφ/dt . The sign φ describe the flux. The flux is proportional to the magnetic field and the area. (φ=BA) In our physic laboratory we realized a very interesting experiment about this law. In this one we introduce a magnet in coil. And we evaluate the emf produce. When you introduce a magnet with a North pole in a coil there is going to be produce an emf negative and if you remove it form the coil is going to be produce a positive emf. This is because the emf produced try to replace the magnetic flux produced. In the case of the magnet remove is produced a positive emf to reestablish the magnetic flux. Wow…really good!!!

I like the magnets and play with them looking their power of attraction. It was one of my favorite themes in physic’s II class. I hope you learn a little bit of these interesting themes…SEE YOU!!!