1. Topic 1 – Electric Charges

2. The Atom
All matter is made of atoms. All atoms are made of protons, electrons and neutrons.
Protons have a
POSITIVE CHARGE.
Electrons have a
NEGATIVE CHARGE.

3. Homework check

4. Attract and Repel Electric discharge
Early scientists were fascinated with what they observed when certain objects interacted with each other.
They proposed the theory that these effects were due to the presence of fluids.
Charles du Fay thought that there were 2 interacting fluids – vitreous and resinous.
Benjamin Franklin thought that there was a single positive fluid.

5. Static electricity Static electricity is due to unbalanced charges.
Static electricity is caused by the movement of electrons.
Static electricity is due to unbalanced charges.

6. Electrical Charge
Positive and negative charges on an object are due to the ratio of protons and electrons present in an object.
Objects are negative when they have more electrons than protons.
Objects are positive when they have less electrons than protons.
Objects are neutral when the amounts of positive and negative charges are equal.

7. CHARGE IT!
All objects are usually neutral until they are acted upon to gain a charge.
FRICTION: where a material is TOUCHED OR RUBBED together then taken apart.
CONDUCTIVE CHARGING: when a charged material touches another material
INDUCTIVE CHARGING: when an electric current is TRANSFERRED to an object when it is close to an electric field.

9. Attract, repel, neutral Some charged objects attract neutral objects
Some charged objects repel each other
Some charged objects attract each other
WHY!?
VIDEO:
Demonstrations
Van Der Graff - Bill Nye
Cayford Magic! (Bending water)

10. Law of Charges There are three types of behaviors that can occur
1. Unlike charges attract
Cleaners and furnace filters
2. Like charges repel
Hair after a sweater is removed
3. Charged objects attract uncharged (neutral) objects
Pants

11. Neutral (uncharged)
Equal positives and negatives
Positive Charge
Excess positives
Negative Charge
Excess negatives

12. Charge Separation
Charged objects cause charge separation when they are brought near to neutral objects

13. Van de Graaff Generators
A Van de Graaff Generator is used to study electrical charges
A rubber belt running in the generator rubs against metal “brushes” and creates a static charge
The charge is then transferred to the metal sphere, where the static charge builds up

14. USES FOR STATIC ELECTRICITY
Let’s think of some together… 1. 2. 3. 4. 5.

15. USES FOR STATIC ELECTRICITY
Let’s think of some together…
1. Collect dirt and dust
2. Photocopiers and laser printers
3. Spray painting cars
4. Defibrillators
5. Annoy a sibling or friend

16. Uses of Static Electricity
Spraying a Car
Positive Car
Negative Spraygun
The paint spreads out as each negative drop repels
No paint is wasted as the positive car attracts the negative paint

17. The Not so Good about Static
SHOCKING!
Clothing sticking after the dryer
Lightning strikes
ROY C. SULLIVAN
7 times struck over a 35 year period.
Ex Park Ranger, lost big toe nail, eyebrows burned off, seared left shoulder, hair on fire, struck in the legs….
Snapping your friend after rubbing your feet across carpet

18. Electrical Discharge
A built-up static charge on an object can be attracted to other objects and jump to the object.
Often this creates a small spark, which is known as an electrical discharge.
Nature always likes to be balanced.
Electrical discharge can cause serious safety hazards
Lightening, shocking people, damage electronics, cause fires, explosions

19. What causes lightning?
Lightning is actually just static electricity on a much larger scale.
The rubbing is caused by air moving around
In thunderclouds bottom is usually negative and top is positive.

20. How do we prevent static build up?
Grounding
By connecting an object to the Earth with a conducting wire, Earth absorbs electrons from a negatively charged object
Chains on a big truck
Ionization
Bounce, anti static spray, etc.

21. Earthing Petrol Tankers
Petrol rubbing against the pipe can build up a static charge which could cause an explosion
The tanker is joined to the ground with a wire to stop a charge building up

22. Mythbusters Van de Graaff generator

23. Insulators and Conductors
Insulators don’t let electrons flow through them
Conductors let electrons flow through them
Electrons stay stuck on the surface and don’t move—
That’s STATIC ELECTRICITY!

24. Superconductors REMEMBER:
Superconductors are materials that offer almost NO resistance to the flow of charges
Materials becomes superconductors when they are put in VERY LOW temperatures
Videos:
Levitate
Levitate Part II
Levitating Train

25. BRAINIACS!
Fun with Electric Fences

26. 1. These forces are responsible for lightning, nature's most spectacular show of electricity …
A. magnetic forces
B. electric forces
C. attractive forces
D. repelling forces
2. Some particles in an atom are charged. Those that are charged negatively are called …
A. neutrons
B. electrons
C. nucleus
D. protons

27. Review Read pages 266-268 in the textbook
Answer questions 1-3 on page 271