A magnetic field can be created by the motion of charged particles, an alternating electric field or the magnetic moments of particles (in permanent magnets).
Magnetic and electric fields are manifestations of one common field - electromagnetic.
The ordered motion of charged particles
The ordered motion of charged particles inConductors is called an electric current. To get it, you need to create an electric field with the help of current sources that perform work on the separation of charges - positive and negative. The mechanical, internal or some other energy in the source is converted into electrical energy.
By what phenomena can we judge the presence of a current in the circuit
Motion of charged particles in a conductorCan not be seen. However, it is possible to judge the presence of a current in a circuit by indirect indications. Such phenomena include, for example, thermal, chemical and magnetic effects of current, the latter being observed in any conductors - solid, liquid and gaseous.
How does a magnetic field
Around any conductor with current existsa magnetic field. It is created by moving electric charges. If the charges are stationary, they produce only an electric field around themselves, but as soon as a current arises, a magnetic field of current also appears.
How can you detect the existence of a magnetic field
The existence of a magnetic field can be detecteddifferent ways. For example, you can use for this purpose small iron filings. In a magnetic field, they are magnetized and converted into magnetic arrows (like a compass). The axis of each of these arrows is set in the direction of the action of the forces of the magnetic field.
The experience itself looks like this. Pour a thin layer of iron filings onto the cardboard, pass a straight conductor through it and turn on the current. You will see how under the action of the magnetic field of current, the sawdust will be placed around the conductor along concentric circles. These lines, along which the magnetic arrows are located, are called the magnetic lines of the magnetic field. The "North Pole" arrows at each point of the field are considered to be the direction of the magnetic line.
What are the magnetic lines of the magnetic field created by the current
The magnetic lines of the magnetic field of the current areClosed curves covering the conductor. With their help it is convenient to depict magnetic fields. And, since the magnetic field exists at all points of space around the conductor, a magnetic line can be drawn through any point of this space. The direction of the magnetic lines depends on the direction of the current in the conductor.