Grade 9 Science: Unit 4: Chapter 2:
The Galaxy and the Universe
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Chapter 2: The Galaxy and the Universe
Chapter 2: The Galaxy and the Universe
Summary of Chapter
Summary of Chapter
Static electricity is one of the two types of electricity. Unlike its counterpart current electricity, it refers to: "the electric charge that stays on the surface of an object after it has been charged". Static means something that *doesn't move*. So therefore, *static* electricity. Electric charges come from electrons, either the presence or absence of them.
REMEMBER: Protons don't move, only electrons do! This is because protons are tightly locked in the nucleus of their atoms, while electrons loosely orbit their atom, and can easily be knocked off of the atom and added to another atom (this forms ions). If you make protons move in a charge diagram, my science teacher will find you and throw a shoe at you. So this means a positive charge is the absence of electrons rather than the presence of more protons.
Epic Static Electricity Simulator: Static PhET Colorado
Basic Intro video (coming soon)
notes and content:
brightness of stars
electromagnetic spectrum
powerpoint stuff
Table of Contents
Table of Contents
Key Terminology of this Chapter:
Key Terminology of this Chapter:
Neutral: Has exact same number of protons as electrons, has a net charge of 0
Charge: An absence or presence of electrons: A state of a material when it is not neutral, has either more electrons than protons (negative charge), or more protons than electrons (positive)
Discharging: The process of making a charged object neutral, via a ground
Ground: A direct connection to the Earth (which is neutral), it is a conductor. This is the best way to make charged objects neutral.
Insulator: An object which does not easily allow objects to flow through it. Electric charges remain static on insulators.
Conductor: An object which easily allows electrons to flow through it. Electric charges do not accumulate on conductors.
Activities:
Activities:
Activity 1: Ecology: Backyard Biodiversity
Activity 1: Ecology: Backyard Biodiversity
brief 1 sentence description.
Link to the assignment: https://docs.google.com/document/d/1zhSMLLcQ8RkT3c2ngqOeDzwba5I9bQaIyLg4LUfwhyE/edit?usp=sharing
Make a Copy of the document
Activity 2: Ecology: Your Local Biome
Activity 2: Ecology: Your Local Biome
brief 1 sentence description.
(transfer biomes activity to a doc)
Link to the assignment: (put link here)
Make a Copy of the document
Biomes Activity: Your Local Biome
Biomes Activity: Your Local Biome
Do some research on what biome you are located in
Suggestions for recording:
Think of the answers to these questions:
What biome are you located in
What level of diversity is in this biome
a. Do some research, what biome and ecozone is the nature area in?
b.
What are the threats to this biome?
How can we protect this biome?
Content
Content
Laws of Electric Charges
Like Newton's laws of motion, these are the important rules you need to know about which electric charges attract each other and which don't.
Like charges repel (positive repels positive, negative repels negative)
Opposite charges attract (positive attracts negative, and vice versa)
Neutral objects are neutral to other neutral objects
All charged objects (+ or -) attract neutral objects (we'll see why later, in Charging by Induction and Induced Charge Separation)
Insulators vs Conductors
Insulators:
Insulator are materials which do not easily allow electrons to flow through them, and thus, are very likely to accumulate static charges.
Good insulators include: plastic, wood, rubber, and clay (ceramics). Many nonmetals are usually good insulators
Conductors:
Conductors are materials which easily allow electrons to flow through them, and thus, are unlikely to accumulate static charges. This property makes conductors very useful in electronics, good conductors of current electricity, they can be used as wires in circuits. (See Current Electricity)
Metals are usually good conductors, due to their electron properties. Examples of good conductors include: copper, gold, platinum.
Semiconductors:
Semiconductors are materials which are between conductors and insulators when it comes to their ability to allow electrons to flow through them. Due to this variable and intermediate property, they are highly prized in electronics.
Examples of semiconductors: Silicon, Germanium, Tellurium, most of the metalloid/semimetal elements on the periodic table.
What is a Ground:
A ground, as mentioned before, is an object that connects directly to the Earth and neutralizes, or discharges electric charges in objects that touch it, by either sending electrons to the object, or taking electrons from the object.
Why are grounds connected to the Earth, you might ask. It's because the Earth is such a large object that it always has a neutral charge overall, and grounding takes place so frequently, that whenever one charge is given to the Earth (positive or negative), its always inevitably cancelled out by the donation of its opposite charge.
For example, if you have accumulated a negative charge (more electrons than protons), and you touch a metal tap (which is the ground in this case, the excess electrons you have accumulated would be sent from you, through the tap, down to the ground, until you have the same number of electrons as protons (have a neutral charge). If you happened to have a positive charge (more protons than electrons), the Earth would send electrons through the ground, to you, until you have enough electrons to be neutral. In both cases, you would feel a static shock.
Common grounds in the house are metal taps: They are conductors, and connect directly to the Earth, via plumbing. So if you wish to make a charged object in your house neutral, for whatever reason, touch it to the nearest tap.
The symbol for a ground (right) is what you would use if you were asked to draw a ground in a diagram.
Triboelectric Series:
Certain materials are more or less prone to gaining electrons when they are subject to Charging by Friction. The objects closer to the bottom of the triboelectric series (occassionally referred to as the electrostatic series) are more likely to gain electrons when they are rubbed with another object. If two objects are rubbed together, the object which is closer to the bottom of the chart (has more electron affinity), would gain electrons, while the other material would lose electrons.
For example, if you rubbed cotton on a glass table, the cotton, having a stronger electron affinity (being closer to the bottom of the table), would take electrons from the glass, leaving the cotton with a negative charge, and the glass with a positive charge.
https://en.wikipedia.org/wiki/Triboelectric_effect
Three Types of Charging:
There are three main ways objects can charge, accumulate static charges.
Charging by Friction:
Charging by friction involves rubbing two objects together
- In charging by friction, two neutral objects are rubbed together and one gets the electrons and the other loses electrons.
- in order to determine which object will get and which will lose electrons we use the electrostatic series
two factors affect the amount of static charge produced :
material (where they are found relative to each other on electrostatic series)
duration/strength of friction
any charge that is transferred onto an insulator will stay where it is transferred
- eg. wherever the electrons were rubbed is where they will stay
two factors that affect the amount of static charge produced are type of material for both objects and duration of friction.
Both items neutral
Items being rubbed onto each other
Affected by triboelectric series
Charging by Contact:
brief touch
one charged, one neutral or opposite charge
not affected by triboelectric series, rather by which object is
Rules of Charging by Contact:
Charging by contact is NOT affected by the triboelectric series, rather by which object is more positive
Object which is more negative gives electrons to object which is less negative
By end of charging by contact, both objects have the same charge.
Charging by Induction:
A way of charging an object without touching it with any charged object.
What's required: A charged object, a neutral object, and a ground.
Steps:
Bring the charged object close to but NOT touching the neutral object. This will result in induced charge separation. (The part of the neutral object close to the charged object will have the opposite charge of the charged object, and the part of the neutral object facing away from the charged object, will have the same charge as the charged object.)
Connect a ground to the side of the neutral object facing away from the charged object. Now electrons will flow into (or out of) the object until that side is neutral. Then remove the ground
DO NOT connect the charged object to the neutral one at any point of this process. After you remove the ground, the charged side of the object would spread out to fill the object. Remember, the charged side of the neutral object has a charge opposite to the charged object, so that charge spreads out.
The objects end up with overall opposite charges relative to each other.
Example with a negatively charged object:
Negatively charged balloon, and neutrally charged box. Negatively charged balloon repels the electrons in the box, has positive charge on side facing balloon. Discharge the negatively charged side of the box
Example with a positively charged object:
Positively charged balloon, and neutrally charged box.
Induced Charge Separation:
no permanent change. Because unlike (above), there is no ground to make object "neutral".
Needs a charged object and a neutral object. This is step 1 of Charging By Induction
Check out this link if you want some additional info on the three types of charging: Three Types of Charging
Content: How does Lightning Work
Lighting is a very powerful source of electricity, far hotter than the sun, an impressive force of nature. But did you expect that the same principles behind you getting a static shock of you rub your feet on a rug, and then touch a metal doorknob, also allow for lightning to happen? Lets see how lightning works below:
Steps of lightning below:
Water droplets evaporate and go up. the water droplets start off neutral because they were on the ground, which is neutral (as we know from Discharging Charged Objects)
The water droplets which enter the clouds from below collide with ice and water droplets (and other precipitation from the clouds) which are heading downwards to exit the clouds, and electrons are knocked off of the water droplets which entered the cloud
The electrons accumulate on the bottom of the cloud, and the positive charge is on the top of the cloud. The electrons can't go to the positive charge at the top of the cloud. The cloud has separated its charges.
The electrons are clustered together at the bottom, which means they do induced charge separation on the neutral ground below, repelling the electrons on the ground. Until the attractive force is so high that the electrons surge down into the ground, by a path of least resistance.
a. This means the lightning is jagged, because dry air is a good insulator, which prevents lightning from reaching the ground. Moist air is a good conductor, and air with positive ions would also attract the lightning (and neutralize bits of it). So the lightning would avoid air with negative ions, and avoid dry air, so meaning its path would be jagged and not perfectly straight.
(diagram of steps below)
Lightning Rods
Lightning rods are pointed metal rods, which are grounded, and so stop the adverse effects of lightning. They attract lightning well because they are very tall too. They can work in one of two ways:
Because a cloud can induce a positive charge on anything below it, which includes the rod, so this repels airborne positive ions, sends them towards the thundercloud, which neutralizes some of the electron charge from the cloud
The positively charged rod attract the electrons of the lightning, and conduct those electrons safely down to the ground.
Bonus content: What is a metal leaf electroscope
a device which is used to help detect if an object is charged.
Chapter Quiz
Chapter Quiz
This short quiz is to test your knowledge on the biodiversity chapter in the ecology unit.
It will be out of 20 points.
Good luck! Remember, this isn't a real quiz. Just to test your knowledge on the unit. So don't stress, just keep calm, and don't worry. This whole site was intended as a study aid. If you do well, good job! Kudos to you. If you don't do so well, it just means you may need to study the section again.
Don't cheat. Please. The chapter quizzes are built into the site as Google Forms, unlike the unit tests, which are external, secure links.
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