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BASIC OPERATION OF A MAGNETIC AMPLIFIER-Cont.
Figure 3-30.Varying coil inductance with a movable coil

Neets Module 08-Introduction to Amplifiers
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3-45 Now, if the value of inductance is decreased to 11.7 millihenries, the formulas yield the following values: So a decrease in inductance of 11.3 millihenries (23 mH—11.7 mH) causes an increase in power to the load (true power) of 625 watts (1125 W—500 W). If it took 1 watt of power to change the inductance by 11.3 millihenries (by some electrical or mechanical means), figure 3-29 would represent a power amplifier with a gain of 625. Q-39. What is the frequency classification of a magnetic amplifier? Q-40. What is the basic principle of a magnetic amplifier? Q-41. If inductance increases in a series LR circuit, what happens to true power? METHODS OF CHANGING INDUCTANCE Since changing the inductance of a coil enables the control of power to a load, what methods are available to change the inductance? Before answering that question, you should recall a few things about magnetism and inductors from NEETS, Module 1—Introduction to Matter, Energy, and Direct Current, chapter 1—Matter, Energy, and Electricity; and Module 2 —Introduction to Alternating Current and Transformers, chapter 2—Inductance. Permeability was defined as the measure of the ability of a material to act as a path for additional magnetic lines of force. Soft iron was presented as having high permeability compared with air. In fact, the permeability of unmagnetized iron is 5000 while air has a permeability of 1. A nonmagnetized piece of iron has high permeability because the tiny molecular magnets (Weber's Theory) or the directions of electron spin (Domain Theory) are able to be aligned by a magnetic field. As they align, they act as a path for the magnetic lines of force.






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