ch35_md

  **Electric Circuits ** 
 * 35.1 A Battery and a Bulb **

When using a battery and a bulb you must complete the circuit, a path from the positive terminal at the top of the battery to the negative terminal at the bottom of the battery.

Electrons with flow from the negative part of the battery through the wire to the side or bottom of the bulb. It then travels through the filament of the bulb and out the bottom, or side, of the battery. It thentravels through anoter piece of wire to the positive part of the battery. This completes the circuit.
 * 35.2 Electric Circuits **

In order for electricity to flow there needs to be a continuous path for it. If there is a break in the path, the current will stop. When you close an electrical switch that connects the circuit, the current flows WHen you open an electrical switch breaks the circuit and the current stops.

There are two types of circuits- A series circuit forms a single pathway for electron flow between the terminals of the batery or other power source. A parallel circuit forms multiple pathways for electrons to flow through

**35.3 Series Circuit**

When the switch in a series circuit is closed, a current flows through all three lamps. A break in the path anywhere creates and open circuit and the electrons cannot flow. an example of a break in the path would be a burning out of one of the lamp filaments or a simple opening of a switch.

Charactoriestics of a series circuit -the current passing through each electrical device is the same, due to the single pathway for electric current. -the total current in the circuit is equal to the sum of the currents through each element -the voltage drop across each element is equal to the curent times the each elements resistance The total voltage in the circuit is equal to the sum of the voltage drops across each element -Ohms law is applied. (the current is equal to the voltage given out by the source, divided by the total resistance of the circuit. The mathematical equation that describes this relationship is: math I=\frac{V}{R} math


 * 35.4[[image:http://www.berkeleypoint.com/images/parallel.jpg width="133" height="235" align="right" caption="http://www.berkeleypoint.com/learning/parallel_circuit.html"]] Parallel Circuit **

Differently from a series circuit, in a parallel circuit, the current in one lamp doesn't pas through the other, therfore, the circuit is completed whether or not all lamps are lit. A break, such as a lightbulb out, does not effect the other paths.

Charateristics of a parellel circuit -Each element of the circuit is contected the the power source by the same two points. This keeps the voltage the same across each element. -The total current in the circuit is diveded between the branches. Therefore, the current travels more easily through brances of low resistance. This causes the amount of current in each brance to be inversly proportional to the resitance. Ohms law is applied seperately to each branch of the circuit. -The total current in the circuit is equal to the sum of all the individual currents within the branches. -The resistance within the circuit decreases as the number of branches increases.. The overal resistance of the circuit is less than the resistance in any one of the branches.


 * 35.5 Schematic Diagrams **

A schematic Digram is made up of different symbols to then represent a circuit. WIRE- these lines are a representation of a wire that connects all the elements in a diagram RESISTOR- all resistors are this symbol but they are labled with different amounts to show the strength of the resistor LAMP- a lamp is shown this way, with a circle around a resistor symbol BATTERY- in the battery symbol, the longer line is a representation of the positive side SWITCH- this is an open switch, a closed switch would have the arm down

<span style="font-size: 150%; color: #aa3131; font-family: 'Lucida Console', Monaco, monospace;">**35.6 Combining Resistors in Compound Circuit**

There are two different ways to find the total resistance within a circuit

Series- to find the total resistance in a series you must add them together. This is because a resistor prevents electricity from going through, if you add another resistor, it is twice as hard for the electricity to get through. That is why you add them together:

Parallel-when adding the resistance together it will be less becasue the current has twice the path width to travel through. When you add the resistance togther, you follow follow the formula- math \frac{1}{R_1} + \frac{1}{R_2} = \frac{1}{R_T} math

The two resistors in parallel are equal to a resistance of 4 total. when added to the 3rd 8 in a series, the total resistance of the circuit is 12.


 * <span style="font-size: 150%; color: #aa3131; font-family: 'Lucida Console', Monaco, monospace;">35.7 Parallel Circuits and Overloading **

A line is what feeds electricity into a home. They are very low in resistance and connected to wall outlets in each room. The voltages that are connected to these lines are applied to appliances, etc. that are connected to the wall plugs. The more devices connected to these lines, the more pathways that are in the circuit. Because the increased amount of pathways reduces the resistance, the current is greater. Lines that carry to much current are considered to be overloading. Over heating can occur and this can be the cause of many house fires.

Preventing overloading- fuses can be used in circuits that effect the entire line current. A safety fuse can handle a certain amount of current and no more. If a current above what the fues can handle is pressed upon it, the fuse will "blow out," which brakes the circuit.

If the insulation that seperates the wires in a circuit is not longer there, the wires can touch. This shortens the circuit and therefore is called a short circuit.

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