Transcript The Control of Electricity in Circuits

The Control of
Electricity in Circuits
Voltage and Current
Static vs. Moving Electric Charges
Recap
Static electricity is electric charge that
remains in a fixed position on an insulator
and distributes itself over the entire
surface of the conductor.
 Static electric charges can be transferred
by friction, contact, and induction.

Static vs. Moving Electric Charges
Current electricity is electrical charge that
moves from a source of electrical energy
in a controlled path through an electric
circuit.
 The electrical energy of the moving
electric charge can be converted into other
desired forms of energy using different
loads (light bulbs etc.)

Electrical Potential (Voltage)
Have you ever wondered why you can
touch some sources of electricity but not
others?
 Such as:

 you
can touch a battery end to end, but not a
wall socket.

This is due to the amount of electrical
energy that is being given by the cell

Energy from the wall can be 80 times
greater than that of a battery.
A Model of Electric Potential:
AKA voltage


We can relate the electric circuit to a watermill
Think of water pouring on a watermill, there is only
so much water in the bucket to pour on the water
wheel, we can call this potential energy
A Model of Electric Potential:
AKA voltage
The energy (water) rotates the wheel
 The same is seen by the dry cell
 The energy in the dry cell or battery is
called the electric potential energy, so
there is only so much energy the battery
can give, the energy released (electrons)
allow the motor to turn.

Voltage
A measure of the potential energy
difference between 2 points in a circuit.
 Big voltage = lots of energy in the
electrons
 This can cause current to flow.

Electricity from Chemical Reactions

Electric Potential:
 The

energy that each electron possesses
This term is interchangeable with the term
Voltage
Its SI unit is a volt (V).
 Can be measured using a voltmeter

Electric Current




Is a measure of the rate at which
electric charges move past a given
point in a circuit.
The variable representing Current is I
The SI unit to measure electric current is
A (ampere)
Current is measured using an ammeter
device which is connected to the circuit
Human Response to Electric Shock
Chart
https://www.osha.gov/SLTC/etools/construct
ion/electrical_incidents/eleccurrent.html
http://www.youtube.com/watch?v=WBBWC
Ax3qfk
Types of Current

Direct Current (DC) – current only flows in
one direction
Types of Current

Alternating Current (AC) – current flows
back and forth at regular time intervals. Eg
generators and electrical sockets use this.
Types of Current
http://www.diffen.com/difference/Alternating
_Current_vs_Direct_Current#Video_compari
ng_Alternating_and_Direct_Current
With imbedded video!
Practice
p438 #(4),5
p447#3-6
If you haven’t started
yet p436#1-3
Electrochemical Cells

There are 2 basic types of primary cells:
The primary wet cell (voltaic cell) and the
primary dry cell.

In a primary cell:
 chemical
reactions use up some of the
materials in the cell as electrons move from it.
Primary Wet Cell

Also called a Voltaic Cell
 developed by Alessandro Volta.

Is called wet because it is made
of two pieces of metal that are
placed in a liquid.
Primary Wet Cell
The 2 metal plates are what’s called
electrodes and are usually copper and
zinc
 The liquid the metals/electrodes are in is
called the electrolyte, which is a liquid that
can conduct a current.
 So what happens in the wet cell?

Primary Wet Cell



The zinc plate is the
negative terminal
The copper plate is
the positive terminal
The energy is only
released when the
cell is exposed to a
closed electrical
circuit
Primary Dry Cell
Functions the same as a wet cell, except
there is no liquid electrolyte, but a moist
electrolyte paste/plate
 Dry cells gradually discharge their energy
over long periods of time, that’s why they
have an expiry date.

Secondary Cells


These are our rechargeable batteries
Secondary refers to the fact that there
are 2 chemical processes occurring
2.
To discharge the cell
To recharge the cell to its original state

Used in cars
1.
Cells and Batteries: Costs and
Benefits


Cells are very convenient, act as a remote
energy source.
In voltaic cells the electrodes themselves are
involved in the chemical reaction (with the
electrolyte), so they can only supply so much
energy before they are fully discharged.
Availability and Cost Resources

Many substances are very rare and only found
in certain areas of the world.

Extracting minerals and elements can be an
expensive process as well.

Rechargeable batteries are used for almost
every type of battery there is.

Rechargeable batteries are much more
expensive to manufacture and may not be worth
purchasing fro low-use devices.
Toxicity
Many of the substances used in cells and
batteries are poisonous
 Such as: lead, mercury, chlorine, Lithium,
Sodium.
 The more batteries, the more these
materials/substances are around us in our
homes.

Disposal
Both rechargeable and single-use
batteries have to be replaced.
 Usually people throw them in the trash and
they go to the land fills.
 50% of the mercury found in landfills are
from batteries.
