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 TRANSFERLearning 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 TRANSFERLearning 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

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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

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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

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Electric eel can discharge 600 V at 1.0 A

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

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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

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CONCEPT 2 – ENERGY TRANSFERScience 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

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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

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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

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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

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CONCEPT 2 – ENERGY TRANSFER Van de Graaff generator

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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

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CONCEPT 2 – ENERGY TRANSFERLearning 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

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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

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CONCEPT 2 – ENERGY TRANSFER Different materials conduct electricity at

different abilities Important to know so devices designed are both

safe and effective

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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

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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

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CONCEPT 2 – ENERGY TRANSFER A polygraph machine (lie detector) is an

application of resistance Measures skin resistance, blood pressure and

respiration

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CONCEPT 2 – ENERGY TRANSFERLearning 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

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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 TRANSFERLearning 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)

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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 TRANSFERLearning 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

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CONCEPT 2 – ENERGY TRANSFER So long as two of the three units are known,

the last one can be solved for

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CONCEPT 2 – ENERGY TRANSFER

Ohm’s Law

Quantity Symbol Unit Equation Measured with …

Voltage V volts (V)

Voltmeter

Current I amps (A)

Ammeter

Resistance R ohms ( )W

Ohmmeter

CONCEPT 2 – ENERGY TRANSFERExample 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 TRANSFERExample A 30-V battery creates a current through a

15-Ω resistor. How much current is created?

CONCEPT 2 – ENERGY TRANSFERExample 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 TRANSFERExample 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 TRANSFERLearning 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

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CONCEPT 2 – ENERGY TRANSFER Using your textbook as a reference (pg 312)

complete the following diagram of electrical symbols

Symbol Represents Description

Conductor

Cell

Battery

Lamp

Resistor

Switch

Ammeter

Voltmeter

Rheostat

Motor

Fuse

CONCEPT 2 – ENERGY TRANSFER A series circuit is one in which the current

passes through each bulb in turn

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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

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CONCEPT 2 – ENERGY TRANSFER Advantages

Household circuits are wired so that it is possible to turn off all the electricity in the circuit

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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

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CONCEPT 2 – ENERGY TRANSFERLearning 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