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I.    What is electric current?

The flow of charges/electrical energy through a solid material (metals)

 II.   Circuits

 A.   Components – wires, switches, motors that are connected to provide a path through which electricity travels.

 B.   Switches – turn circuits on and off

 C.   Circuit diagram (schematic)

 1.    Wire –         straight line

 2.    Battery         Image

 3.    Resistor              




4.    Switch         Image



D.      Resistors – any electrical component that uses energy.


E.   Open circuit – When a switch is in the off position; breaks prevent current


F.    Closed circuit – When a switch is in on position; current flows


III.  Charges


       A.   Kinds – positive and negative


B.       Electrostatic forces – forces between positive and negative charges; because most objects are neutral, they hold many objects together.


C.       Protons and Electrons – electrons stay within the atom because they are attracted to the protons in the nucleus.



IV. Voltage


A.   Battery – is chemical energy used to move charge particles through a wire


B.   Volts – measure the energy level at a certain place in a circuit.


1. A 1.5 volt battery – adds 1.5 joules of energy that leaves the positive end of a battery.


2. When a battery dies – there is not enough energy to push the charges through the circuit.


C.   Measuring Voltage – negative terminal assigned 0 V, all other places on the circuit relative to this value.  All points on a wire are the same voltage.


D.   Usage – When energy (chemical from battery) is used, voltage drops


V.   Current – is a flow of electric charges.


A.   Flow – from high voltage to low voltage (plus to minus)


B.   Charges – already present in the wire; battery repels electrons in the wire, which

repel other electrons in the wire, etc.


C.   Voltage vs. Current – voltage supplies energy to make charges flow; current carries energy.


D.   Ampere – unit for the measurement of current


E.   Circuit breaker – prevents the current from becoming damaged if too much current is received.


F.    Alternating current – direction of current in the circuit goes back and forth (as in your home).


G.   Direct current – battery only makes current flow in one direction.


VI. Resistance


A.   conductor – allows current to pass through it easily


B.   insulator – prevents the passage of electric current


C.   Resistance – a measure of how easily charges flow through an object.


1. Units – ohm (W) is the unit of resistance


2. Ohm’s Law – the current in a circuit is directly proportional to the voltage and inversely proportional to the resistance.


3. Current = Voltage/Resistance or I = V/R




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Last update: Thursday, January 31, 2013