• Define d.c current
• State the analogy between current flow and water flow
• Describe basic d.c. circuits
2.1 DIRECT CURRENT
Direct current is that current which flows in only direction at a time. The d.c. circuits normally contain a battery, which is the source, and this battery has two terminals namely: Negative and Positive terminals as shown in figure 3.1 below.
2.2 ANALOGY BETWEEN CURRENT FLOW AND WATER FLOW
The three main concepts in electricity are voltage, current and resistance. Voltage or potential difference can be thought of as the driving force (although it is not really a "force") behind the electric current. In the water analogy, in figure (3.2), you can think of voltage as the pressure difference created by a pump that causes the water to flow through the pipe in the water system. Also you can think of the electrons flow in the electric circuit as equivalent to the flow of the water in the pipes that caused by the pump.
Another important concept in electricity is resistance. It’s Property of a material that opposes the flow of electrons through it. There is always a resistance flow between two points in a pipe. This is analogous to the resistance (R) in an electric circuit.
2.3 BASIC D. C. CIRCUIT
A basic d.c. (direct current) circuit consist of an electrical connection of a d.c power source (e.m.f source), connecting wires and a load as shown in Fig 3.3. In this case, the load can be any electrical component (e.g. a resistor) or a network of resistors. The d.c. power sources such as dry cells (such as used in flash lights), car batteries and laboratory d.c power supply unit. The symbol of a d.c source is as shown in Fig. 3.3. It is represented by two vertical lines, with the longer line marked (+) and the shorter line marked (-).
No comments