Electrical Engineering ⇒ Topic : Solenoid
A long coil of wire consisting of closely packed loops is called solenoid.
The word solenoid comes from Greek word meaning 'tube-like'. By a long solenoid we mean that length of the solenoid is very large as compared to its diameter. When current is passed through the coil of air-cored solenoid, magnetic field is set up as shown in Fig. (a). The path of the magnetic flux is made up of two components :
(1) length /1 of the path within the coil
(2) length l2 of the path outside the coil.
The total m.m.f. required for the solenoid is the sum of m.m.f.s required for these two paths i. e.
Total m.m.f. = m.m.f. for path /1 + m.m.f. for path I2
But m.m.f. for path /1 *>> m.m.f. for path I2
Total m.m.f. = m.m.f. for path /1
Hence, for a solenoid (air-cored or iron-cored), the length of the magnetic circuit is the coil length /1. We can use right-hand rule to determine the direction of magnetic field in the core of the solenoid.
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