Unit D - Electricity

Week 1

1.1 STATIC ELECTRICITY

I can…

• Distinguish between static and current electricity, and identify examples of each

Static electricity

• Static electricity is a stationary electric charge• What does stationary mean?

• The charge is not flowing like a current• Ex. Lightning, static electricity on clothing,

“shocking people” by touching them, shock from your car.

Electrical charge

• Remember that opposites attract which is true of negative charges

• Most objects have an equal number of positive and negative charges so they are considered neutral

• When an object has more of one charge we say it is charged

• Ex. An object with extra electrons is negatively charged

Draw this picture in your Notes!Positive Charge = Protons

Negative Charge = Electrons

Electrical discharge

• Static electricity does not continue to flow, but it can undergo electrical discharge

• The build up charge on an object can be attracted to another object and jump to that object

• We call the spark an electrical discharge

Laws of electrical discharge

• Opposite charges attract each other• Like charges repel each other

Charge separation• Charged objects cause a charge separation

when they are brought close to neutral objects

• For example, a negatively charged balloon, when brought close to a wall will cause the negative particles in the wall to be repelled, and therefore will be attracted to the positive particles left in the wall.

Van de graaf generator

• Used to study electrical discharge• Good at building up static electricity• Produce a static build up using friction (collect

extra electrons on the metal sphere)

Van derGraff Activity

• Before the Activity – What happens when you rub a balloon on your head? (Volunteers?)

• Write down your observations from the following tests:

• 1. Hole punch dots on the top• 2. Use the grounding electrode• 3. Making hair stand up. • 4. Making a chain of people

Review Questions

• What is the difference between a proton and an electron?

• What does it mean to be “statically charged”?• How do like charges interact?• How do unlike charges interact?• A neutral object contains no charge. Is this

true?

1.2 CURRENT ELECTRICITY

I can…

• Distinguish between static and current electricity, and identify examples of each

• Identify electrical conductors and insulators, and compare the resistance of different materials to electric flow

Introduction

• Read the first paragraph on page 279 as a class• Is the charge on the eel a static charge or a

current?

Electrical Current

• Static charges can discharge but they are not useful for operating electrical devices because they do not flow continually

• The steady flow or charged particles is called electrical current

• Electrical current can be used to run electrical devices as long as 2 things occur

The necessary parts to a Circuit

• 1) Conductor- wire• 2) Energy Source- battery or outlet• 3) Load- the thing that uses the electricity• 4) Control- often a switch

Conductor

• A conductor allows electricity to move through it easily

• What are examples of conductors?

• What is the opposite of a conductor? What are examples of these?

Insulators

• Draw the examples from page 298• in an insulator the electrons are bound tightly

to the nuclei so they resist movement

• 2) Conductor with no voltage applied: the electrons are not as tightly bound to the nuclei. They can drift away from the nuclei but do not flow in any one direction

• 3) Conductor with voltage applied: the electrons flow towards the positive terminal of the voltage source

Conductors and insulators

• When would you want to use a conductor in a circuit?

• When would you want to use an insulator in a circuit?

Circuits

• A circuit is a path that controls the flow of electricity

• Usually electricity moves through solid wires but it can move through gases or other fluids

• Open and Closed Circuits

Electrical Power Grid

• An electric power grid creates energy at a generating station (can be through many different means). At the station electrical energy is created

• The electrical energy is sent through high-voltage lines to businesses and residential areas

• What are the different types of generating stations that create electricity for us?

Quick Lab

• With a partner do the following lab– you have 20 minutes – 1) Using any materials, make one light bulb light up– 2) Using a battery, one bulb and 1 wire, make the light

bulb light up– 3) Using any materials, make 2 light bulbs light up– 4) Make 2 light bulbs light up so that when you

unhook one bulb, the other goes out– 5) make 2 light bulbs light up so that when you

unhook one bulb, the other stays on

2.3 ANALYZING AND BUILDING ELECTRICAL CIRCUITS

I Can…

• Draw and troubleshoot circuit diagrams for a variety of specific purposes.

• Explain how switches and resistors can control electrical flow, and predict the effects of these changes on output in a circuit.

Types of circuits

• The most economical way to design a circuit is in a loop

• However, we do not always want every part of the circuit being dependent on the others in the circuit

• Ex. Would it be convenient for a plug-in to only work if the light switch was on?

Other types of Circuits

• Series Circuits• Parallel Circuits

Series circuit

• In a series circuit there is only one pathway for the current

• If the pathway is interrupted the circuit cannot function

• Problem: adding more things increases the total resistance light bulb will get dimmer as we add more

Parallel circuit

• Parallel circuits have a current path for each section of the current

• A break in one pathway does not affect the others

• Adding more pathways decreases the total resistance

Circuit drawing

• We use special (easy to draw) symbols to represent parts in a diagram

• An electrical diagram is called a schematic• 4 parts of a circuit– Source – Conductor – Switch or control – Load

Lets draw parts for our Schematic Diagram

Symbol Represents Description

Conductor Conducts electricity through a circuit

Cell Stores electricity (large bar is positive)

Battery Combination of cells

Lamp/ Light Bulb Converts energy to light

Resistor Controls the amount of current in the circuit

Symbol Represents Description

Switch Opens and closes circuit- allows current to flow

Ammeter Measures the amount of current in a circuit

Voltmeter Measures voltage across a device in a circuit

Rheostat Variable resistor

Motor Converts electricity to mechanical energy

Fuse Melts if current in circuit is too high

Tips for drawing schematics

• Conductors are always drawn in straight lines with 90 degree angles

• The symbols are made the same size• Conductor lines are not allowed to cross

Example

Complete the Circuit Assignment in your notes.

1. A closed circuit with a two-cell battery, a bulb and a switch.2.

An open circuit with a three-cell battery, a bulb and a switch. 3.

A closed circuit with a three-cell battery, two bulbs, a switch and an voltmeter4.

A circuit with a two-cell battery and two bulbs that can are controlled by one switch.5.

A circuit with a three-cell battery and two bulbs, each of which are controlled independently by a switch.

Practice 1

• Draw a schematic in a loop made from:– A battery– 2 light bulbs– A switch– Conductors (Wires)

Practice 2

• Draw a schematic diagram in a series including these things–Resistor– Switch–Voltmeter– Fuse–Battery made of 3 cells

Practice 3

• Draw a schematic diagram in parallel with the following:–2 cells that power the whole circuit–A light turned on by one switch–2 more lights turned on by a switch

together–A third switch that turns on or off all the

lights together

Lets read!

• As a class read about House Wiring and Microcircuits on page 315

• What is a transistor?

• What is a microcircuit?

1.3 – ELECTRICAL SAFETY

I can…

• Assess the potential danger of electrical devices, by referring to voltage and current rating (amperage) of the devices, and distinguish between safe and unsafe activities.

Review

• What is the difference between static and current electricity?

• What are some examples of conductors and insulators?

• What four things do we need to have in a circuit?

• Electricity moves through the path of least resistance– where it is the easiest to flow

• A short circuit is a circuit where there isn’t any protection and the electricity moves quickly and can cause damage

• The 3rd prong on a cord leads to the ground and is called a ground wire

• The number of amps of a current is more important in terms of the danger of being shocked

• Current from 0.015 A to 0.020 A will cause a painful shock and loss of muscles control

• What does this mean for a person being shocked?

• A current as low as 0.1 A can be fatal

The dangers of electrical shock

• To protect yourself from electric shock you never want to allow electricity to run through you

• Why are you safe in your car if a power line fell on it?

• When are you not safe?

Factors affecting electrical shock

• Different situations affect how bad an electrical shock is

• One a dry day with running shoes on you may just feel a tingle from an electrical fence, but the same fence on a rainy day when you are barefoot could really hurt

Protecting yourself from Electrical Shock

• Every plug in device in Canada must have a label on it showing what voltage it requires and what current it can use

• The higher these numbers the more harm it can do

• http://www.youtube.com/watch?v=n6DXkVY8fzs

• http://www.youtube.com/watch?v=DtoQbXzNqkg&list=PLyxsgbmjwCCkYdJ6Y2anojKwKXJVqiu9V

Electrical safety pointers

• Read the blue box on page 285 and choose three points to write down

Plugs, Fuses and breakers

• Fuse: contain a very thin piece of metal that will melt if too much current flows through it stopping the circuit–Need to be replaced (like in a car)

• Breakers- they “ short out” when too much current is sent through them–Need to be cooled (like in your home)

Danger of lightning

• A lightning strike can give a current up to 30 000 A and it can kill

• Lightning usually strikes at the highest point on a horizon

• Lightning rods are connected to the ground through a wire to allow the discharge to dissipate to the ground

• http://www.youtube.com/watch?v=RLWIBrweSU8• http://www.youtube.com/watch?v=XKMdYbOfFzI

Demonstration

• Blow a Fuse!• http://www.youtube.com/watch?v=ZT3HhDj8

bRk• http://www.youtube.com/watch?v=pJ9e4eaOi

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1.4 CELLS AND BATTERIES

I Can…

• Investigate and evaluate the use of different chemicals, chemical concentrations and designs for electrical storage cells. (explain functions of parts and diagram)

Electrochemical Cells

• An electrochemical cell is a package of 2 types of metals and an electrolyte

• One metal has more free for electrons than the other metal, so when a wire is attached to create a circuit the electrons get to move from one metal to the next, which creates a current

Types of cells

• Cells can power tiny pacemakers, toys, cars or computers

• There are 2 types of cells–1) Dry cells- the electrolyte is a paste–2) Wet cells- uses a liquid electrolyte

Dry Cells• The electrolyte in a dry cell allows ions to flow

which completes the circuit• An ion is an atom with a charge• Positive terminal- where electrons travel back

to the cell• Negative terminal- where electrons travel

from the cell

Dry Cells

• The 2 metals are called electrodes• One electrode becomes positively charged,

and the other becomes negatively charged.• ALKALINE (having a basic electrolyte)- are

some of the most common dry cells• What does alkaline mean again?

Wet cells• Wet cells often have a liquid such as sulfuric acid as their

electrolyte• They are usually cheaper and easier to make than dry cells

but are more dangerous• Vehicles use wet cells that need to be disposed of properly• There are individual cells that alternate within the battery• Each cell has a positive and a negative plate• The terminals in the battery are at the top

Think about it!• Is it correct to call a car battery a battery?

Wet Cell Batteries

Primary vs. Rechargeable cells

• Primary cells: cells that can only be used one time

• Rechargeable cells aka secondary cells- can be reused, the chemical reaction that occurred originally is forced to go back so it can be used again

• Ni-Cd batteries are common secondary cells (made up of nickel and cadmium)

Battery

• Society today does not use the work battery correctly

• A battery contains more than one cell• http://www.youtube.com/watch?v=TBQDGvhr

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Electrochemistry• Alessandro Volta made the first practical battery around 1800

by stacking copper and zinc disks with an electrolyte solution• Other scientists used batteries to split molecules into their

elements electrolysis (ex. Water used as a fuel for rockets by breaking into oxygen and hydrogen)

• Electrochemistry was begun which is the study of chemical reactions involving electricity

• Scientists discovered that by putting more than one cell together they could increase the current and the power of the battery

• https://www.youtube.com/watch?v=8oeUE6dlP2A

Electroplating

• Electroplating uses the technology of a battery in reverse to create a layer of silver or gold on an object

How to electroplate

• The metal that is to be coated is immersed in an electrolyte solution with metal bar in it.

• The metal ions bond on the object and become a solid metal deposited on top of the less expensive materials

• http://www.youtube.com/watch?v=z7f7dQF2KLA

2.1 CONTROLLING THE FLOW OF ELECTRICAL CURRENT

I can…

• Draw and troubleshoot circuit diagrams for a variety of specific purposes.

• Explain how switches and resistors can control electrical flow, and predict the effects of these changes on output in a circuit.

A Unique circuit

• Neon signs have neon gas in them, when electricity is run through them they glow.

• The circuit needs to be complete and needs to be controlled carefully

Superconductors

• Some metals are better conductors than others because they give less resistance to the electrons that are flowing

• Superconductors are perfect conductors- they have no resistance to electron flow– Extremely low temperatures help reduce

the resistance in the superconductors–What’s the issue to running a

superconductor at a low temperature?

Resistors

• Resistance is a measure of how difficult it is for electrons to flow through a substance

• A resistor uses power (a load can be a resistor)• Resistance is measured in ohms –symbol Ω

(omega)• The more resistance a substance has the more

energy it takes from the electrons that pass through it

Switches and Variable resistors

• Switches allow the control of a circuit by simply shutting it “on” or “off”

• A variable resistor or a rheostat can adjust the resistance in an object that the current flows through

• Ex. Volume control on stereos, dimmer light switch

Lets read!

• Last paragraph on page 300 and paragraph on page 301

• What kind of water conducts electricity?

• What kind of water does not conduct electricity?

• How does a polygraph work?