المجال المغنطيسي في الوشيعة - اهمية المغنطيسية .. الإلكترونيات

Magnetic field in a coil - The importance of magnetism .. Electronics

Magnetic field in a coil

When an electric current passes through a certain coil, the core becomes inside it. If the core is pulled outside the coil, the resulting magnetic forces work to pull it inside (65). The fixed iron legs and couplers around the coil work to concentrate the magnetic field to increase the magnetizing force of the magnetic attraction that works to insert the core inside the coil.

It should be noted that we often need to avoid magnetic fields as usually happens in non-induced wire-wound resistors. Then, the resistance wire is wrapped so that the field in one section cancels the field of the other section (66).

There are different ways to achieve this. In Figure (66), we see a wire-wound resistor that resembles an electromagnet. This resistance has a self-inductance that can be eliminated by making the resistance in the form of a ring (66b) so that the direction of the current passing through one of the wires is opposite to the direction of the current passing through the other wire. As for Figure (66c), it is possible to cancel the resulting magnetic fields by using thin mica strips wrapped around the wire so that each half of the language is on the side of

65 - Coils

66 - Non-inductive resistors with wrapped wires

67 - The deflecting magnetic field of the cathode ray

of the strip. Figure (66d) represents a coil whose coiling method has been reversed in the middle. It is known that electrons are affected by the presence of magnetic fields. This effect is used in television tubes and magnetrons: the stream of electrons is emitted from the electron gun in the cathode ray tube (67), then passes between two pairs of coils. If the current does not pass through these coils, the electron beam travels in a straight line and collides with the fluorescent screen, creating a bright spot in its center.

If an electric current passes through the coils, an electromagnetic field is created in them that causes the beam to deviate and bend upwards or downwards and to the right or to the left as needed. Thus, the beam can be directed to collide with the screen at the desired point that was previously determined.

The intensity of the resulting magnetic field and the polarity of the current passing through the coils are changed in a specific way so that each pair of them is perpendicular to the other pair as in Figure (68). We can also control the movement of the beam and direct it so that it passes on Which part of the image tube face do we want to display as in television sets?

68 - Arranging the coils around the cathode ray tube.