Section 2 Current

Voltage and Current Electrical Potential Energy: the ability to move an electrical charge from one point to another. Depends on position in the electric field

Potential Difference Potential Difference- between any two points the work that must be done against electric forces to move a unit charge from one point to another Measured in volts (V) Common unit used for batteries

Voltage in batteries Batteries help power many things in our daily lifes Range from 1.5 V to 12 V Cell: a device that is a source of electric current because of a potential difference or voltage between the two terminals

Dry and Wet cells Batteries contain an electrochemical cell. Each cell has an electrolyte and two electrodes on either end Dry cells have a paste like electrolyte that helps conduct electricity Wet cells contain a liquid electrolyte

Dry vs. Wet cell

Current Electricity flows from the negative to the positive terminal Current: The rate that electric charge moves through a conductor Measured in ampheres

Electrical Resistance Resistance: the opposition posed by a material or device to the flow of a current. Conductors have low resistance Insulators high resistance

Resistance Equation resistance = voltage/current R= V/I SI unit is ohm Ω (greek letter omega) Resistor special kind of conductor used to control the rate of flow in an object

Resistance Problem The headlights of a typical car are powered by a 12 V battery. What is the resistance of the headlights if they draw a 3.0 A pf current when turned on?

Example problem Current = 3.0 A Voltage = 12 V Resistance =? Equation  R= V/I R= 12 V/ 3.0A R= 4.0Ω

Try this one Find the resistance of a portable lantern that uses a 24 V power supply and draws a current pf 0.80 A?

Solution R= V/I R= 24V / 0.80 A R= 30Ω

Superconductors Metals that have zero resistance when they fall below certain temperatures Temperatures range from -272°C to - 123° C Used in filters, magnets and high speed trains

Semiconductors Contains properties of both conductors and insulators In a pure state semiconductors are insulators Controlled amounts of materials added to the semiconductor control its ability to conduct an electrical charge Common examples- computer boards

Circuits Section 3

Warm-up Discuss amongst your group which circuit would conduct the most electricity: A parallel circuit or an open circuit

Electrical circuits When we want to light a lightbulb with wires and a battery all the parts must be connected in order for electricity to flow A set of electrical components connected such that they provide one or more complete paths for the movement of charges

Closed circuits Circuits that provide a closed loop for electricity to flow around Occurs when the wires are connected to the battery and the lightbulb in a closed loop

Open circuit When one part of the circuit is missing the electricity can not flow This type of circuit is called an open circuit

Switches When applied to a circuit you can switch the circuit from open to closed When the lights are on the circuit is closed when they are off the circuit is open.

Schematic designs A graphical representation of a circuit that uses lines to represent wires and different symbols to represent components Because schematic devices use standard symbols they can be read by people all over the world.

Series circuit The components of a circuit that form a single path for current Since there is only one path for the electricity to flow the time it takes to charge this item is the same

Parallel circuit A circuit in which all of the components are connected to each other side by side The current in each item doesn’t have to be the same. Even if we remove a bulb from the circuit the other light bulb would light

Electrical Energy The energy that is associated with charged particles because of their positions Electric power: rate at which electric energy is used in a circuit

Electrical Power Equation Power = current x voltage P=IV SI Unit watt (W)

Example When a hair dryer us plugged into a 120 V outlet it has a 9.1 A current in it. What is the hair dryer’s power rating?

Steps to solve problem V= 120V I = 1.9 A P= VI P= 120 x 1.9 P= 1.1 x 10 ^ 3 W

Try this one An electric space heater requires 29 A of 120 V current to adequately warm a room. What is the power rating of the heater?

Solution P= VI P= 120 X 29 P= 3480 W