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A DC term that means the voltage is lower than 0.
You can have it plus or minus the zero point
The National Model Railroad Association in the USA is the largest organization devoted to the development, promotion, and enjoyment of the hobby of model railroading. The NMRA was founded in 1935 in Milwaukee, Wisconsin in order to provide a service to the hobby of model railroading. It is responsible for defining the standards for DCC control systems.
Nor is a gate term used to describe logic components.
NOR gate (NOR = Not OR)
This is an OR gate with the output inverted, as shown by the 'o' on the output.
The output Q is true if NOT inputs A OR B are true: Q = NOT (A OR B)
A NOR gate can have two or more inputs, its output is true if no inputs are true.
Types of transistor: There are two types of standard transistors, NPN and PNP, with different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon. If you are new to electronics it is best to start by learning how to use NPN transistors.
See also: Transistors