Transcript Concept 2 - RF Staples Secondary School

Concept 2
Energy Transfer
CONCEPT 2 VOCABULARY TERMS
Static electricity
 Proton
 Electron
 Neutral
 Charge separation
 Electrical discharge
 Electrical current
 Circuit
 Amperes (A)

Conductors
 Load
 Voltage
 Potential difference
 Volt (V)
 Voltmeter
 Short circuit
 Insulators
 Fuses
 Circuit breakers

CONCEPT 2 VOCABULARY TERMS
Electrochemical cell
 Dry cell
 Electrolyte
 Ion
 Electrode
 Wet cell
 Primary cell
 Rechargeable cell
 Secondary cell
 Battery

Electrolysis
 Electrochemistry
 Electroplating

CONCEPT 2 – VOCABULARY TERMS
Conductor
 Insulator
 Resistor
 Resistance
 Ohms (Ω)
 Variable resistor
 Rheostat
 Ohm’s Law
 Ammeter
 Schematic

Schematic diagram
 Series circuit
 Parallel circuit
 Transistor
 Microcircuit

CONCEPT 2 – ENERGY TRANSFER
Learning Concept

Investigate and evaluate the use of different
electrodes, electrolytes and electrolytic
concentrations in designing electrical storage cells
CONCEPT 2 – ENERGY TRANSFER

Recall:
Chemical energy is transformed into electrical
energy in battery-powered devices
 An electrochemical cell is a device which has
different metals in a solution containing a salt or
acid

CONCEPT 2 – ENERGY TRANSFER

In an electrochemical cell, there are two metal
electrodes surrounded by an electrolyte, a
substance that can conduct electricity
CONCEPT 2 – ENERGY TRANSFER
Learning Concept
Assess the potential danger of electrical devices,
by referring to the voltage and current rating
(amperage) of the devices
 Distinguish between safe and unsafe activities

CONCEPT 2 – ENERGY TRANSFER

Two aspects of electricity must be considered
when looking electrical dangers

Voltage


The measure of how much energy is carried by each
particle
Ampere

The rate at which an electrical current flows
http://i881.photobucket.com
CONCEPT 2 – ENERGY TRANSFER
High voltage is more dangerous than low
voltage
 Small voltages can kill if the shock carries a
significant amount of amps


The number of amps is more important than
voltage when assessing potential danger
http://static.newworldencyclopedia.
org
http://wpcontent.answcdn.com
CONCEPT 2 – ENERGY TRANSFER
50,000 V is more likely to kill than 10 V
 0.001 A passed through your body won’t likely
be felt
 Current in the range of 0.015 A to 0.02 A causes
a painful shock and loss of muscle control


Currents as low as 0.1 A can be fatal
Electric eel can discharge 600 V at 1.0
A
www.aqua.org
CONCEPT 2 – ENERGY TRANSFER

Taser (stun) guns can
carry up to 50,000
volts


Can deliver up to
1,500 V to a person’s
body
Small current of 0.002
to 0.03 amps
http://thebsreport.files.wordpress.com
http://www.cbc.ca/news/canada/story/2009/03/18/f-taser-faq.html
CONCEPT 2 – ENERGY TRANSFER
Electrical outlets in
Canada deliver 120
volts of electricity
 A light bulb draws
about 0.5A while a
toaster pulls 5A
 Possible to suffer fatal
shock from a
household outlet

http://www.cbc.ca/news/canada/story/2009/03/18/f-taser-faq.html
CONCEPT 2 – ENERGY TRANSFER
Science Log
 Make a list of 5 safety pointers for use with
electrical devices (reference pg 285)

ex. Do not use electrical devices when near or in
water unless they are specially designed
www.auctionpax.co.uk
CONCEPT 2 – ENERGY TRANSFER

Learning Concept

Distinguish between static and current electricity

Identify example evidence of each
CONCEPT 2 – ENERGY TRANSFER

Recall:
The proton has a positive charge
 The electron has a negative charge


Most objects have equal amounts of positive
and negative charges, which makes them
neutral
CONCEPT 2 – ENERGY TRANSFER

Charge separation occurs when charged
objects are brought close to neutral objects
http://4.bp.blogspot.com
CONCEPT 2 – ENERGY TRANSFER
Rubbing the balloon
on your hair transfers
electrons (e-) from
your hair to the
balloon
 Bringing the charged
balloon to the wall
repels the e- in the
wall but attracts the
protons

CONCEPT 2 – ENERGY TRANSFER

The Laws of Electrical Charges
Opposite charges attract each other
 Like charges repel each other

http://learn.uci.ed
CONCEPT 2 – ELECTRICAL ENERGY

Electrical discharge is observed as a spark

Static energy does not flow in a current but can
build up and discharge



Electrons build up in your body
Doorknob becomes positively charged as “your”
electrons repel the doorknob electrons
“Your” electrons are attracted to the doorknob’s protons
www.school-for-champions.com
CONCEPT 2 – ENERGY TRANSFER

Van de Graaff generator

http://www.youtube.com/watch?v=7qgM1A3pgkQ&fea
ture=related
http://1.bp.blogspot.com
http://4.bp.blogspot.com
CONCEPT 2 – ENERGY TRANSFER


While static energy builds up and discharges, it
does not flow continuously
Electrical currents are steady flows of charged
particles

This is the type of energy used to operate electrical
devices
http://upload.wikimedia.org
CONCEPT 2 – ENERGY TRANSFER
Learning Concept
 Identify electrical conductors and insulators

Compare resistance of different materials to
electric flow
CONCEPT 2 – ENERGY TRANSFER

Insulators do not allow for easy transfer of
electrons away from the nucleus

Tightly bound to the nuclei
http://glassian.org
CONCEPT 2 – ENERGY TRANSFER

In a conductor the electrons are more loosely
bound so they can move away from the nuclei

Current will only flow if the conductor is hooked to
an electrical source
www.diy-guides.com
www.copper.org
CONCEPT 2 – ENERGY TRANSFER

Different materials conduct electricity at
different abilities

Important to know so devices designed are both
safe and effective
www.mutr.co.uk
CONCEPT 2 – ENERGY TRANSFER

A resistor is a type of conductor

Allows current to pass but applies a resistance to it


Limits amount of electric current to pass
Resistance is a measure of how difficult it is for electrons
to flow through a substance
www.yksd.com
CONCEPT 2 – ENERGY TRANSFER

Resistance is measured in ohms


Symbol is the Greek letter omega, W
The more resistance a substance has, the more
energy is gained from each electron passing
through it
www.electronicsandyou.com
CONCEPT 2 – ENERGY TRANSFER

A polygraph machine (lie detector) is an
application of resistance

Measures skin resistance, blood pressure and
respiration
www.mentalfloss.com
CONCEPT 2 – ENERGY TRANSFER
Learning Concept
 Use switches and resistors to control electrical
flow

Predict effect of these devices and others in an
application
CONCEPT 2 – ENERGY TRANSFER

A switch is the best method for turning
electricity on and off
Basic principle: when on, two conductors are
pressed together and electrons can flow
 When off, the conductors are not in contact, and
electron flow is interrupted

www.web.net
www.edupic.net
CONCEPT 2 – ENERGY TRANSFER

A variable resistor, or rheostat, is used to
increase or decrease the amount of current in
a circuit slowly
Dimmer light switch
 Volumes on stereos
 Foot-operated speed controls on sewing machines

CONCEPT 2 – ENERGY TRANSFER
Learning Concept
 Describe, using models, the nature of electric
current
 Explain the relationship between current,
resistance, and voltage
CONCEPT 2 – ENERGY TRANSFER

Recall:
Current looks at how quickly an electrical charge is
able to move (amps)
 Voltage looks at how much charge is carried in the
electrical current (volts)
 Resistance is a measure of how difficult it is for
electrons to transfer (ohms)

www.websters-online-dictionary.net
CONCEPT 2 – ENERGY TRANSFER
CONCEPT 2 – ENERGY TRANSFER

The hydo-flow model has several components
Water in the container
 Amount of water pouring from the spouts
 Force of gravity on the water
 Diameter of the spout

CONCEPT 2 – ENERGY TRANSFER
Learning Concept
 Measure voltages and amperages in circuits

Apply Ohm’s law to calculate resistance, voltage
and current in simple circuits
CONCEPT 2 – ENERGY TRANSFER

German scientist Georg Simon Ohm proved a
mathematical link between voltage (V), current
(I) and resistance (R)
CONCEPT 2 – ENERGY TRANSFER

Ohm’s law states that as long as temperature
remains the same
Resistance of a conductor stays the same
 Current is directly proportional to the voltage
applied

www.sengpielaudio.com
CONCEPT 2 – ENERGY TRANSFER

So long as two of the three units are known, the
last one can be solved for
http://cyberchalky.files.wordpress.com
CONCEPT 2 – ENERGY TRANSFER
Ohm’s Law
Quantity
Symbol
Unit
Equation
Measured
with …
Voltmeter
Voltage
V
volts
(V)
Current
I
amps
(A)
Ammeter
Resistance
R
ohms
(W)
Ohmmeter
CONCEPT 2 – ENERGY TRANSFER
Example
 An electrical stove is connected to a 240-V
outlet. If the current flowing through the stove is
20-A, what is the resistance of the heating
element?
CONCEPT 2 – ENERGY TRANSFER
Example
 A 30-V battery creates a current through a 15Ω resistor. How much current is created?
CONCEPT 2 – ENERGY TRANSFER
Example
 A motor has an internal resistance of 40-Ω. The
motor is in a circuit with a current of 4.0-A.
What is the voltage?
CONCEPT 2 – ENERGY TRANSFER
Example
 A current of 625-mA runs through a bulb that is
connected to 120-V. What is the resistance of
the bulb?
CONCEPT 2 – ENERGY TRANSFER
Learning Concept
 Develop, test and troubleshoot circuit designs
for a variety of specific purposes
CONCEPT 2 – ENERGY TRANSFER

A circuit is simply a complete path that
charged particles can flow through

Often drawn with symbols in an image known as a
schematic or a schematic diagram
www.bin95.com
CONCEPT 2 – ENERGY TRANSFER

Using your textbook as a reference (pg 312)
complete the following diagram of electrical
symbols
Symbol
Represents
Conductor
Cell
Battery
Lamp
Resistor
Switch
Ammeter
Voltmeter
Rheostat
Motor
Fuse
Description
CONCEPT 2 – ENERGY TRANSFER

A series circuit is one in which the current
passes through each bulb in turn
www.electronicsandyou.com
CONCEPT 2 – ENERGY TRANSFER

Disadvantages


If the pathway is
interrupted the whole
circuit cannot function
Adding components
increases the total
resistance

Adding another bulb
would make all the
lights dimmer
www.sciencephoto.com/
CONCEPT 2 – ENERGY TRANSFER

Advantages

Household circuits are wired so that it is possible to
turn off all the electricity in the circuit
http://images.meredith.com
CONCEPT 2 – ENERGY TRANSFER

Parallel circuits have separate current paths for
each section of the circuit

Each bulb would have its own path to the current
source
CONCEPT 2 – ENERGY TRANSFER

Advantages
An interruption or break in one pathway does not
affect the rest of the pathways
 Adding extra resistors decreases the total
resistance in the circuit

http://i.ehow.com
CONCEPT 2 – ENERGY TRANSFER
Learning Concept
 Identify similarities and differences between
microcircuits and circuits in a house
CONCEPT 2 – ENERGY TRANSFER
Define transistor
 Define fuse


Use page 315 of your textbook to compare and
contrast microcircuits and household wiring