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