FIG. 14. Diagram showing how Lines of Force Form about a Loop of Wire.
If a wire is connected to a battery or some other source of electric current and a portion of the circuit twisted so as to form a loop, the entire space enclosed by the loop will be a magnetic field and possess magnetic properties.
By forming a wire into a spiral coil the combined effect of each individual turn is concentrated in a small space and a powerful field of force is produced. If the coil is provided with an iron core, the lines of force can be concentrated and will exercise a very powerful attractive effect upon any neighboring masses of iron or steel. Such a coil is called an electromagnet. A hollow coil without any core is called a solenoid.
FIG. 15. Magnetic Phantom about a Coil of Wire.
Solenoids and electromagnets play a very important part in the construction of most electrical instruments.
The strength of an electromagnetic coil is proportional to its ampere turns. The ampere turns of a coil are obtained by multiplying the number of amperes flowing through the coil by the number of turns of wire composing it.
LESSON SIX. DYNAMO ELECTRIC MACHINERY.
The Dynamo. The Alternator. The Motor.
The discovery of the induction of currents in wires by moving them across a magnetic field led to the construction of electrical machines, called dynamos, to generate current in place of batteries.