Tuesday, May 18, 2010

Let there be light

A DC circuit is a circuit in which the voltage and current throughout the circuit are constant. For a simple DC circuit, as shown in the picture to the left, all of the elements need to be connected. For example, if one of the light bulbs in the circuit was unscrewed, then the other light bulb would go out, and the whole system would stop. Throughout this circuit, the voltage and current is constant. So if the battery was a 5 volt battery, the voltage throughout the entire system would be 5 volts. The same idea applies to the current. The current running through the entire circuit is constant, meaning that if you used an ammeter to measure the current throughout the circuit, then you would find that the current is constant.

Another type of circuit is the parallel circuit as shown to the left. In this circuit, one of the light bulbs could be unscrewed and the other would still be lit. In this circuit, the voltage throughout is constant just like in the circuit above. The current, however, is a little different. In each light bulb the current is half of the total current in the circuit, meaning that when the currents in the parallel are added their sum is equal to the total current in the circuit.

The circuit shown to the left is a more complex circuit which includes two light bulbs in a parallel circuit in a series with another light bulb. So if one of the light bulbs in parallel was unscrewed the others would still be lit, but if the third light bulb was unscrewed, all of the lights would go out. The voltage throughout the entire system is constant as it is in the two situations above, but the current, however, is not. The current running through the single light bulb is equal to the total current and the current through the bulbs in parallel is half that of the total current like in the parallel circuit above.

1 comment:

  1. Great diagrams!
    You did not explain the characteristics of a DC circuit which was the first question of the assignment.
    In the first circuit you said: " the voltage and current throughout the circuit are constant." What exactly do you mean by that? Isn't that the case for ALL circuits? If that wasn't the case there would be a violation of conservation laws (charge for current and energy for voltage). In the two other circuits you claim that current is not constant. Perhaps you could have explained the flow of electrons through various paths and how that works.
    Though you do a great job explaining what happens in a circuit when an element is disconnected, you were supposed to clearly explain how current through the circuit and voltage across each element work.
    Please be sure that you understand how the circuits work as it is an important part of the final exam.