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Module-3 http://www.aircrafttechtrng.com
1. Hydrogen bubbling on the surface of the ANODE of a battery is
called polarization. Itmakes the battery useless, but can be
prevented by using certain chemicals in the electrolytecalled
depolarizers.
2. A linear actuator brake coil is wired in series with the main
field. So if it burns out theactuator will stop working.
3. The definition of a semiconductor is '4 electrons in the
outer shell'.Silicon, germanium and carbon are all
semiconductors.
4. Decreasing the frequency of a circuit may damage any
inductors in thecircuit. The reactance of inductors reduces as
frequency reduces, so theydraw more current, and may burn out.
5. The dielectric in a capacitor stores electrostatic
energy.
6. Integrating a step input voltage produces a ramp voltage, or
a sawtooth waveform.
7. The magnetic field of a motor is distorted in the opposite
direction tothe rotation of the armature. The magnetic field of a
generator is distortedin the same direction as the rotation of the
armature. Both these arecalled Armature Reaction.
8. To remember which lags what in AC circuits, remember CIVIL
-Capacitor(C) - I lags V, Inductor(L) - V lags I.
9. B.C.A.R.s: do not in themselves constitute law. However,
failure to comply can also meanfailure to comply with the ANO,
which can mean prosecution in a civil court. The onlysanction the
CAA can apply is the withdrawal, or revocation of any
certificates,authorisations and/or licenses they have issued.
10. To change the direction of a DC motor, you must reverse the
current flow through either the field winding or the armature
winding, but not both.
11. Glass is a good example of a diamagnetic material. It will
spread the lines of magneticflux, and when suspended in a magnetic
field, will rotate to 90 to the field.
12. A paramagnetic material has a relative permeability of
greater than unity (a vacuum isunity). This means it is easier for
magnetic flux to go through it than it would a vacuum, andit will
concentrate the lines of flux.
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13. The coercive force is the magneto motive force required to
drive out residual magnetismfrom a material. This means that when
the coercive force is applied, there is no magnetismin the
material.
14. The voltage of a cell is dependant upon the chemicals used
in the cell only. Changing thesize of the plates will only change
the amp.hour rating, not the voltage.
15. The heaviest part of an atom is the neutron, but it is so
close to the mass of the protonthat most people consider them the
same.
16. The lightest part of an atom is the electron, at nearly
1/2000th the mass of either the proton or the neutron.
17. To remember the left and right hand rule, remember MG (the
British car manufacturer).From left to right the left hand is for
Motors, the right hand is for Generators. TheAmericans use a
different current direction, they would remember GM (the American
car manufacturer) i.e. left hand for Generators and right hand for
Motors.
18. Nicad batteries should be stored fully discharged
(dissipated). Often a metal rod is put between the terminals to
ensure they are fully discharged. Lead Acid batteries must bestored
fully charged and checked every 30 days.
19. The outer casing of a mercury battery is the anode, and is
therefore the positive terminal.
20. Electrolytic capacitors must only be used with DC
(polarised) circuits. They are used because they are physically
small for their capacitance.
21. The frequency of an AC power curve is twice the frequency of
the current or voltagewhich caused it.
22. Placing a resistor in series with the field of a shunt wound
motor will INCREASE themotor speed. This is because it reduces the
BEMF in the armature and the armature thendraws more current.
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