Real World Instrumentation with Python

DC Circuit Characteristics

Now let’s examine the lamp and battery circuit in Figure 2-4 more closely. It may seem simple, but there is actually quite a bit going on here.

When the lamp is connected to the battery, closing the circuit, current will flow through the lamp and then return back to the battery. If it were an open circuit, there would be no current flow and no light (switches are often used to open or close circuits). Generating current flow in a circuit requires a power source capable of producing some volume of electrons (the current) at a voltage (the electrical potential) sufficient to operate the circuit.

When electrical current flows through a circuit, there is always some amount of resistance to the flow; even wires have some resistance. A circuit with low resistance will move current more easily than a circuit with high resistance, and the high-resistance circuit will require a higher voltage to achieve the same level of current flow as the low-resistance circuit. For example, a circuit with a 10-volt supply and 50 ohms of resistance will conduct 0.2 A (also stated as 200 mA, or milliamps—thousandths of an ampere) of current. If the resistance is increased to 100 ohms and we still want to maintain 200 mA of current, the voltage will need to be increased to 20 volts. A high-resistance circuit will also dissipate more power (heat) than a low-resistance circuit at the same current. We’ll have more to say about this a little later.

Ohm’s Law

As you may have already surmised, ...