- Electronics Engineering/Electronics fundamentals
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Welcome to the course EE 112.
- EE Electronics_fundamentals
- Resistors Ohms law, watts law, LEDs, homemade
- capacitors impedance, homemade
- inductors impedance, homemade
- Mid-term Exam
- Diodes silicon zenner germanium shotkey
- Transistor as a switch Intro to BJT
- JFET and MOSFET as a switch Intro to FET technology
- Final Exam
They are devices that oppose the flow of current. They are measured in ohms Ω, may be connected in series or parallel, and are found in many electrical components. Example, in Light Emitting diodes (LED's) resistors are connected in parallel to LED's to reduce the amount of current entering it likewise it is connect in series to capcitors e.t.c.
Capacitors consist of two conducting plates separated by an insulator (in primitive capacitors this insulator consisted of an air gap). When a capacitor is charging, electrons accumulate on one of the plates and through electrostatic repulsion cause the opposite plate to become positively charged. Electrostatic repulsion on the negative plate also acts as a resistive force (or voltage) to incoming electrons. When the negative plate reaches saturation (the point at which no more electrons can be crammed onto the plate), we can therefore say the capacitor is "charged". If the voltage applied exceeds the resistive capabilities of the insulator, "dielectric breakdown" occurs in which a bridge (path of least resistance) is formed from one plate to the other.
A hydraulic comparison is a pipe with a section of rubber stretched across the cross-section. When pressure (voltage) is applied on one side, the rubber stretches. This forces water out the other end briefly and causes the rubber to resist being stretched any further. If the water pressure exerts too much force, the rubber ruptures, allowing the water to flow freely.
In this mode of charging we can therfore say "current leads voltage". This will become more important when discussing AC circuitry.
Inductors are in their simplest form, a coil of wire. To understand how an inductor works, one needs to remember that a magnetic field is produced by a changing electric potential. In this case our electric charges are electrons. As an electron changes its direction (by moving through the coil), it also changes its velocity thereby producing a magnetic field. The magnetic field itself requires energy to fully form. This energy is removed from the electron's momentum as it travels through the wire, causing a braking force on the electron itself. This braking force is registered as voltage. Once the magnetic field becomes fully formed, its energy requirements drop considerably. This allows electrons to flow more freely through the inductor. We can then say that the inductor is "charged".
A hydraulic comparison is a paddle wheel. At first, considerable water pressure is required to overcome the wheel's kinetic coefficient of friction. However once the wheel is up to speed, the water only needs to overcome its dynamic coefficient of friction, which is considerably less.
Both the dynamic coefficient of friction of the paddle wheel and the hysterisis effect of the magnetic field produce heat. In this way, overcharging an inductor can burn it out.
By the effects of an inductor charging, we can say that "voltage leads current". Again, this will become more important in AC circuitry.
|NPN||ON 2n3904||ON 2n2222||Fairchild TIP29||Fairchild TIP41||Fairchild TIP142|
|PNP||ON 2n3906||ON 2N2907||Fairchild TIP30||Fairchild TIP42||Fairchild TIP147|
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, Engineering circuit analysis, William H. Hayt Jr., 2007, McGraw-Hill Higher Education