Electrical symbols
Electronic component are classed into either being Passive
devices or Active devices. A Passive Device is one that contributes no power
gain to a circuit or system. Examples are Resistors, Light Bulb, Electrical
Heaters. Active Devices are components that are capable of generating voltages
or currents. Examples are Batteries and other Electrical Curent & Voltage
Sources.
By using schematics symbols we can represent real-life devices.
Resistance -This is a resistance, measured in units ohms ohms, . Most often it
will be a resistor.
 This is
a source of emf (electromotive force) or voltage source, with a voltage of ,
measured in units of volts, V. The most common source you will see will be a
battery. However, batteries are really not resistance-free. We can model this
case by putting a 'resistor' in the circuit which has the same resistance as the
batterys would have.
 This is a
current source, with a current of , measured in units of amperes , A. Current
source is ideal model of electrical power source. The internal current source
resistance is infinity. We can model real life battery by putting a 'resistor'
in parallel with curent source.
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