Electrical Circuits Chapter 20 Section Three

Science Journal Entry #42 Expound upon Ohm’s Law and its relationship to current, resistance, and voltage.

Circuit Diagrams An electric circuit is a complete path through which charge can flow. An electric circuit is a complete path through which charge can flow. Circuit diagrams use symbols to represent parts of a circuit, including a source of electrical energy and devices that are run by the electrical energy. A circuit diagram shows one or more complete paths in which charge can flow. Circuit diagrams use symbols to represent parts of a circuit, including a source of electrical energy and devices that are run by the electrical energy. A circuit diagram shows one or more complete paths in which charge can flow.

Open or Closed Circuits Switches show places where the circuit can be opened. If the switch is open, the circuit or path has been broken and the current stops. When a switch is closed, the circuit or path is complete and charge can flow. Switches show places where the circuit can be opened. If the switch is open, the circuit or path has been broken and the current stops. When a switch is closed, the circuit or path is complete and charge can flow. Is the switch in this picture open or closed? Is the circuit broken? Is the switch in this picture open or closed? Is the circuit broken?

Types of Circuits There are two types of circuits: series circuits and parallel circuits. There are two types of circuits: series circuits and parallel circuits. In a series circuit, charge has only one path through which it can flow. If one light bulb burns out to a series circuit, it becomes an open circuit. So if one element stops functioning in a series circuit, none of the elements can operate. In a series circuit, charge has only one path through which it can flow. If one light bulb burns out to a series circuit, it becomes an open circuit. So if one element stops functioning in a series circuit, none of the elements can operate. A parallel circuit is an electric circuit with two or more paths through which charges can flow. If one element stops functioning in a parallel circuit, the rest of the elements still can operate. A parallel circuit is an electric circuit with two or more paths through which charges can flow. If one element stops functioning in a parallel circuit, the rest of the elements still can operate.

Series and Parallel Circuits and Corresponding Diagrams

Direction of Current Verses Direction of Electron Flow The direction of current is the direction in which positive charges flow. The direction of current is the direction in which positive charges flow. When the energy source is a battery, the current flows from the positive terminal to the negative terminal. When the energy source is a battery, the current flows from the positive terminal to the negative terminal. The electrons move in the opposite direction. The electrons move in the opposite direction.

Sources of Resistance Resistance is the opposition to the flow of charges in a material. Resistance is the opposition to the flow of charges in a material. The bulbs in a circuit are sources of resistance. The bulbs in a circuit are sources of resistance. The series current decreases as a result of this resistance and light bulbs shine less brightly. The series current decreases as a result of this resistance and light bulbs shine less brightly.

Power and Energy Since power is the rate of doing work, electric power is the rate at which electrical energy is converted to another form of energy. Since power is the rate of doing work, electric power is the rate at which electrical energy is converted to another form of energy. The unit for electric power is joule per second, or watt (W). The unit for electric power is joule per second, or watt (W). Electric power is usually measured in thousands of watts, a unit called a kilowatt (kW). Electric power is usually measured in thousands of watts, a unit called a kilowatt (kW). Electric power can be calculated by multiplying voltage by current. Electric power can be calculated by multiplying voltage by current. P (watts) = I (amps) x V (volts)

Electrical Energy An appliance’s power rating informs the consumer as to how much power it uses under normal conditions. To find the amount of electrical energy an appliances uses, multiply power x time. If a clothes dryer uses 5400 watts how much would that be in kilo-watts? If the dryer is in use for 2 hours, how much energy would it use in kilowatt hours? A kilowatt-hour is equal to 3,600,000 joules. So how many joules would be used in 2 hours by this dryer?

Circuit Problem Correct wiring, fuses, circuit breakers, insulation, and grounded plugs help make electrical energy safe to use. The average voltage in the circuit of an average household is 120 volts. The amount of current in a circuit will vary. When there are two many devices that are turned on in a parallel circuit, the increase in the current may exceed the circuit’s safety limit. When this happens, the wire may overheat and start a fire.

Opening a Circuit Fuses and circuit breakers keep a home safe by providing an open circuit when the current becomes too high. The is like the open switch that we spoke about previously. An open circuit like an open switch, breaks the path of the current which means that the current may no longer flow until a fuse is replaced or a breaker reset.

Fuses, Circuit Breakers and Insulated Wiring A fuse prevents an overload when a wire in the center of the fuse melts if too much current passes through it. The fuse must be replaced with a new fuse before the circuit can carry current again. Most modern houses have circuit breakers rather than fuses. A circuit breaker is a switch that opens when current in a circuit is too high. Electricity would not be available for the circuit until the circuit breaker is reset. Electrical wiring in a house is insulated to protect people but if the insulation is damaged electrical shock through bare spots may occur.

Personal Safety To avoid electrical shock, never touch electrical devices with wet hands. Damaged insulation may cause short circuits. Short circuits occur when current finds a short path through the circuit with less resistance than the full path through the circuit. A three-prong plug can prevent shocks caused by short circuits because the third prong connects to the ground providing an easier path to ground through the grounding wire rather than traveling through your body. The transfer of excess charge through a conductor to Earth is called grounding.