1. Grade 9 Academic Science RH King Academy
Unit 3: Electricity
Grade 9 Academic Science
RH King Academy

2. Unit Outline Static electricity Electroscope lab Current electricity
Circuit lab
Electrical energy
Energy ISU

3. What is electricity? Recall from chemistry: what is an electron?
An electron is a negatively charged particle in an atom
Electrons can move! They transfer between atoms, giving them positive and negative charges
If a substance gains electrons, what charge does it have?
NEGATIVE
If a substance loses electrons, what charge does it have
POSITIVE
Electricity is the flow of electrons

4. Static electricity Static charges collect on surfaces
They remain on surfaces until they are given a path to escape
Why do you think this girl’s hair sticking to the balloon?
Read along on p.394

5. Demonstration of charge
Materials:
Fur
Plastic pen
Bits of paper
Procedure
Sprinkle bits of paper on the counter
Rub the pen roughly against the fur about 10 times
Hold the pen above the bits of paper. What do you observe?

6. What happened? You observed static electricity
Recall, what is electricity?
When you rub a balloon against your hair, or you rub plastic against fur, you build up static charges
These charges build because as you rub these two objects together, you are transferring electrons
The fur LOST electrons. It became POSITIVE.
The pen GAINED electrons. It became NEGATIVE.
These charged objects were then able to attract objects with opposite charges.

7. Transferring electrons
How do atoms lose or gain electrons?
One common cause of electron transfer is friction – when objects rub against each other
The diagram below shows amber and fur being rubbed together. The fur transfers its electrons to the amber.
As electrons are tiny, note that millions of electrons are being transferred, not just a few.

8. Charges
When electrons are transferred, the object that loses the electrons is positively charged, and the object that gains the electrons is negatively charged.
If the two objects weren’t rubbed together, they would have remained neutral. However, when they were rubbed together, electrons were transferred, so they became charged.
Amber gained electrons
Fur lost electrons

9. Electron Affinity
How do you know if an object will lose or gain electrons?
Some materials have a tendency to lose electrons, while others have a tendency to gain electrons.
This is called electron affinity.
Refer to the table of Triboelectric series. This will tell you if the material will lose or gain electrons.
Refer to p. 398

10. 1) If you rubbed cotton and Teflon together.
What charge would the cotton be?
What charge would the Teflon be?
2) If you rubbed silk and nylon together.
What charge would the silk be?
What charge would the nylon be?
3) If you petted a cat.
What charge would your hands be?
What charge would the cat be?
4) If the cat rolled around on a cotton blanket
What charge would the cotton blanket be?

11. Laws of Attraction and Repulsion
Remember: “opposites attract”
Positive and negative charges attract
Like charges (positive and positive / negative and negative) repel
If you increase the amount of charge, the attraction or repulsion also increases

12. Example
If you rubbed hair against a nylon balloon, what would the charges be?
The hair would be positive, the balloon would be negative.
Notice that her hairs are spreading apart. That’s because they are positively charged, and they are repelling each other (like charges repel!)
But her hairs are also sticking to the balloon. That’s because her hairs are positively charged, but the balloon is negatively charged (opposite charges attract!).

13. How do you measure charges?
An electric charge is measured in coulombs (C)
1 coulomb = 6.24 x 1018 electrons added to or removed from a neutral object
Never seen scientific notation before? means move the decimal 18 places to the right.
Therefore, that’s electrons.
1 coulomb sounds like a lot of electrons! But remember, electrons are tiny.

14. Insulator and Conductors
Not all materials transfer electrons easily. If that were the case, the electricity running through all these wires around us would flow right into our bodies.
Some materials conduct electricity, while others insulate electricity.
Conductors allow electrons to flow freely. Examples: copper, aluminum, mercury, or any other metal.
Insulators resist the movement of electrons. Examples: rubber, plastic, pure water.
Fair conductors allow some movement of electrons. Examples: carbon, mineral water, human body.

15. Insulators and Conductors

16. How insulators and conductors work together
Metals are “conductors”. This means that electrons flow freely through them.
For this reason, electrical wires are made of metal. They conduct electricity (which means they allow electrons to flow through them).
Plastics are “insulators”. This means that they resist the movement of electrons.
For this reason, electrical wires are coated in plastic. They insulate electricity (which means they prevent electrons from flowing)
We rely on metal conductors to bring us electricity, but we also rely on plastic insulators to prevent us from getting shocked by electricity.

17. Is water a conductor? Pure water is an insulator
You may have heard that it’s dangerous to be in the water when lighting may strike. This is true. So does that mean that water isn’t an insulator?
Only pure water is an insulator. The water in lakes and rivers is not pure. It has minerals in it. Therefore, it’s a fair conductor.

18. Lesson Review Questions
Answer these questions now in your own words:
Define electricity.
Explain how objects get charged.
How do you know whether an object will lose OR gain electrons?
What is the difference between a conductor, fair conductor, and insulator?

19. Homework
P. 398 #1-5
P. 401 #1-5