TRANSFORMERS. REMOTE CONTROL. OHM’S LAW

№ 12. TRANSFORMERS

A transformer is used to increase and decrease the voltage of an electric power supply. A transformer is a static machine. It has no moving parts. It consists of two coils of wires which are wound around a soft iron core. The coils are called windings, one is primary, and the other is the secondary. When a current is passed through the primary winding, a magnetic field is up around the iron core which induces a voltage in the winding. If the number of turns in the secondary is greater than the number in the primary it is a step-up transformer and the output voltage is greater than the input. A step-down transformer reduces the input voltage.

№ 13. REMOTE CONTROL

It is sometimes convenient or economical to operate electronic apparatus from a distance. This is known as remote control and it may be brought about by the use of a relay which is really an electro-magnetic switch. A relay consists of an electromagnet. The latter attracts a soft iron armature. The armature is returned to its former position by a spring when the electromagnet is deenergized and therefore there is no longer any attraction. The movement of the armature opens or looses the contacts of the relay. In this way one electrical circuit can be used to control another.

№ 14. OHM’S LAW

The practical unit of electrical resistance, ohm, was named after the German mathematician and physicist Ohm. He discovered that a simple correlation exists between three of the basic electric quantities: resistance, current and voltage. He found that if the resistance of a wire is constant, the current passing through it is proportional to the potential difference maintained, as long as the temperature of the conductor remains unchanged. Ohm also observed that the greater the resistance, the smaller the current. Ohm’s two observations can be put together in a simple statement. The current that flows in a circuit is directly proportional to the voltage and inversely proportional to the resistance. It is the statement that is generally called Ohm’s law.

⇐ Предыдущая 1 2 3 456 7 8 9 Следующая ⇒