Air-core coils

Chapter Air-core coils

Teach Yourself Electricity and Electronics Third Edition Book
Pages 748
Views 14,327
Downloads : 46 times
PDF Size : 4.4 MiB

Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • Problem 10-6There are two coils with values L1835µH and L22.44 mH. They are connected inseries so that their coefficient of coupling is 0.922, acting so that the coils oppose eachother, as shown in Fig. 10-6. What is the net inductance of the pair?Air-core coils18910-5Illustration for Problem10-5.10-6Illustration for Problem10-6.First, calculate M. Notice that the coil inductances are specified in different units.Convert them both to microhenrys, so that L2 becomes 2440 µH. Then M0.922(8352440)1/21316µH. The total inductance is therefore LL1 L2 2M835 2440 2632643µH.It is possible for mutual inductance to increase the total series inductance of a pairof coils by as much as a factor of 2, if the coupling is total and if the flux reinforces. Con-versely, it is possible for the inductances of two coils to cancel each other. If twoequal-valued inductors are connected in series so that their fluxes oppose, the resultwill be theoretically zero inductance.Air-core coilsThe simplest inductors (besides plain, straight lengths of wire) are coils. A coil can bewound on a plastic, wooden or other nonferromagnetic material, and it will work verywell, although no air-core inductor can have very much inductance. In practice, themaximum attainable inductance for such coils is about 1 mH.Air-core coils are used mostly at radio frequencies, in transmitters, receivers, and an-tenna networks. In general, the higher the frequency of an alternating current, the lessinductance is needed to produce significant effects. Air-core coils can be made to have