SNC 1DO LESSON PLANS

The concepts of static and current electricity will be explored in this unit. Skills in using a variety of instruments will be developed in order to gather qualitative and quantitative data.

Ontario Curriculum objectives: U=understanding concepts (U1-U15) D=developing skills  (D1-D10) R=relating science (R1-R4)

Text: Sciencepower 9, McGraw-Hill

-rub two materials together
-this results in a build up electrons on a material (-) or loss of electrons from the material (+)




Conduct producing Negative Charge:
-when a negative object touches neutral object and gives e- to the neutral object
-both objects now have extra e-, and both objects are now negative

-bring a charged object near to a neutral object
-no direct contact occurs between the two objects, but e- move within a substances resulting in charging


   

TERMS (symbols are in text)
SOURCE -origin of electrical energy (e-) that can flow through circuits (eg. dry cells, generators)

ELECTRICAL CONDUCTORS -wires that provide a controlled path fro the flow of electrical current (made of
                                              conductors such as copper or other metals)

ELECTRICAL LOAD -device that converts electrical energy into useful energy (eg. heat, mechanical, sound, light)
                                    eg. light bulb, motor 

SWITCHES -device that controls electric current, allowing or preventing current passage (eg. fuse, circuit breaker,
                     switch)

-resistance is a property that inhibits (slows) electrical motion and converts electrical energy into other energy forms
-more resistance = harder to  push coulombs of charge through an area
eg. a light bulb filament slows electron flow and converts the electrical energy into light

Resistance = potential difference across a load / current through a load =R (units = ohms...see text for symbol)
R (ohms) = V (volts) / I (amps)

eg. what is the resistance of a heating coil with a current of 12.5 A connected to a 120 V wall outlet?
R = V/I
   = 120 V / 12.5 A
   = 9.60 ohms

RESISTORS -devices that provide resistance, and are useful for controlling current or voltage to suit certain electrical devices
Symbol for Resistors and Variable Power Supply are in text

TEMPERATURE
-the higher temperature, the greater the resistance (it is harder for electrons to flow through disorganized, fast moving electrons)
LENGTH
-increase resistance with increased wire length (resistance doubles as length doubles...it is harder to flow greater distances relative to shorter distances)
CROSS SECTIONAL AREA
-decrease resistance with larger area in wires (more area for electrons to flow allows for easier flow)
MATERIAL
-the structure of atoms may allow electrons to move easily or poorly, depending on how well atom holds onto electrons (material with a poor hold on electrons provides little resistance)

POWER: the amount of energy that can be converted into heat, light, sound, etc. per second

Power (units = W...watts) = Energy (J) / Time (s)
P = E/t

Also,
P = VI

Work on resistance lab to discover find R_T = Total Resistance in a circuit

In Series:
Total Resistance is equal to the sum of resistance caused by each the resistors in the circuit

R_T =R₁ + R₂ + R₃ + ....

In Parallel:
One divided by the Total Resistance is equal to the sum of on divided by the the resistance caused by each of the resistors in the circuit

1/R_T =1/R₁ + 1/R₂ + 1/R₃ + ....

Energy is defined as the ability to do work
-some forms of energy are "potential" or stored

-electrical energy can be converted into other types of energy. These include:
    radiant (e.g. electromagnetic waves of light)
    thermal (e.g. heat)
    chemical potential (e.g. stored energy in food)
    gravitational potential (e.g. stored energy in a rock on hill)
    elastic potential (e.g. stored energy in stretched or compressed objects)
    nuclear potential (e.g. stored energy in the center of an atom)
    kinetic (e.g. the energy of a moving object)
    sound (e.g. the energy of vibrating objects)

-an energy system is a device that converts one form of energy into another
eg. electric kettle converts electrical energy into sound and thermal energy

FIRST LAW OF THERMODYNAMICS -"energy is not created or destroyed, it just changes forms"
 
       INPUT ENERGY  = WASTE ENERGY + USEFUL OUTPUT ENERGY

input energy = amount of energy used to operate a system
output energy = amount of useful energy obtained from a system
waster energy =energy that is not useful (often thermal)
unit of energy = Joule (J) = 1000 J = 1 kJ (kilojoule)

ENERGY EFFICIENCY =[ENERGY OUTPUT / ENERGY INPUT]  X 100

eg. 500 kJ energy goes to electric kettle, which uses 490 kJ to heat water, and loses 10 kJ as heat and sound

kettle efficiency = E out/ E in  X 100
                       = (490 kJ / 500 kJ) X 100
                       = 98 % efficiency

waste = 100 % - 98%
          = 2 % energy wasted

-electrochemical cells convert chemical potential energy into electrical energy

PRIMARY CELLS (disposable energy sources)
-materials undergo chemical reactions producing electrical current
-when the chemical reaction is complete, the primary cell is no longer useful as an energy source

(a) VOLTAIC CELLS are wet primary cells
     -to make a voltaic cell, two pieces of metal (electrodes) placed in liquid (electrolyte)
      ELECTRODES -metal conducting plates placed into solution eg. pieces of Zn, Cu
      ELECTROLYTE -liquid that conducts electrical current eg. H₂SO_{4 (aq)}

e.g. Zn reacts with H₂SO_{4 (aq)} with Zn+ moving into the electrolyte H₂SO_{4 (aq)} and pushing out the H₂
-the solution will build up a positive charge (as it gains Zn+ ions), and will release hydrogen gas
-electrons are left behind on the remaining Zn electrolyte 
-these negative electrons leave Zn electrode (anode = loses electrons)
-the electrons then flow through copper wire conductor to positive electrolyte solution
-before they enter the electrolyte solution they pass through the other electrode (cathode = gains electrons)
-this electron flow continues until chemical reaction has ended and no more Zn is left to react with the H₂SO_{4 (aq)}

(b) DRY CELLS are dry primary cells
    -these work like a wet voltaic cells but the electrolyte used is a moist paste (not a liquid)
     advantages = less chance of spilling electrolyte
                           explosive hydrogen gas is not produced

BATTERY = collection of dry cells (see text for symbol)

SECONDARY CELLS (reusable energy sources)
-a voltaic or dry cell that can regain it's charge and be used indefinitelyd

-begin on energy research project

NEUTRAL WIRES: These wires carry no electrical current into the house
WHITE WIRE: one wire entering home is neutral. It is grounded and goes to ALL appliances
This wire is attached to 120 V devices, and provides for a potential difference

GREEN WIRE: an ground wire should go to larger loads as a third wire,
This wire is attached to a basement pipe as a safety device in case wire comes loose

HOT WIRES -these wires carry electrical current into the house
RED WIRES: carry + 120 V of electrical energy
BLACK WIRES: carry -120 V of electrical energy
Larger devices are connected to red and black wires, providing a potential difference of 240 V
Smaller devices get 1 hot wire (red or black) and 1 white wire, providing a potential difference of 120 V

DIRECT CURRENT (D.C.) = electrons travel continuously in one direction
ALTERNATING CURRENT (A.C.) = electrons rapidly change direction back and forth
-your house is usually wired with 240 V and alternating current (A.C.) as it is economically cheaper to produce and send long distances, while most labs done this unit use direct current