# Circuit Theory/IV curves

These curves reflect that most circuits are designed with voltage as the independent variable; with voltage sources and currents being dependent variables. What this means is that the slopes of the IV curves are 1/R. So normally whereas normally horizontal is a slope of 0, it is now a slope of infinity. The current–voltage characteristics of four devices: 100K ohm, 10 ohm, a P–N junction diode, and a battery with real world internal resistance. The horizontal axis is voltage drop, the vertical axis is current.

Ideally, a diode would turn on at 0 volts and go from horizontal to vertical instantly.

Ideally, a voltage source would be a vertical line.

Ideally, resistance does not change due to voltage or current and are thus straight lines.

A transistor is understood through the above type of graph. The horizontal lines represent current source behavior. Notice how the current stays constant while the voltage changes.

The angled straight lines coming out of the origin represent "linear" behavior where the transistor is operating like an amplifier. The horizontal lines are where the "linear" behavior stops and the current source behavior begins.

Understanding what is controlling this and why the many blue lines starts with understanding what the three wires into a transmitter do: