Static Electricity

1. Static Electricity

2. What is Static Electricity • The buildup of electrical charges in one place. • Static = charge does not move or flow • (usually a temporary condition). • Can be detected by an electroscope.

3. Examples of static electricity: • Rubbing a balloon on your hair • Walking across carpet • Clothes tumbling in dryer • What do these have in common? Friction!!!!

4. Creating Static Charges • Static charges result when some charges are transferred from one object to another by friction • Which charges are easily removed? • Recall structure of the atom.

5. Recall from Chemistry • Electrons (-) are on the outside of the atom so they can be easily removed, while protons (+) are held firmly in the nucleus • Protons & Neutrons • Electrons

6. Two Types of Charge • Electrons can be transferred by friction, but protons cannot • Transferring protons would create a new element! • LOSING electrons gives an object a POSITIVE charge • GAINING electrons gives an object a NEGATIVE charge • NOTE: When one object loses, another must gain - electrons can’t be created or destroyed

7. BEFORE Combing transfers electrons from the hair to the comb by friction, resulting in a negative charge on the comb and a positive charge on the hair. AFTER

8. Induced charge • Charged and neutral objects (not touching) are attracted because electrons move in the neutral object. • Electrons move toward a +ve charged object and away from a –ve charged one. • This is called “induced charge”

9. Conduction • Conduction = direct transfer of charge • Eg: walk across carpet and touch a doorknob  shocking! • Electrons are stripped from the carpet and you gain a net –ve charge • When you touch the doorknob, electrons jump onto it  electrical discharge

11. Place an “X” in the appropriate box:

12. Place an “X” in the appropriate box:

13. Rules of static electricity • Objects with like charges repel, but objects with unlike charges attract • Charged objects attract neutral objects

14. Does friction always create static charge? • Different materials have different strength of attraction for electrons • If two objects of the same material are rubbed, no static charge forms • (equal number of electrons transfer each way)

15. If two different objects are rubbed, they have different attractions to the e- • The stronger one will take e- away from weaker one and static charges build up

16. Uses of static electricity • Trapping particles in smokestacks of factories • Applying grit to sandpaper • Spray painting mesh (e.g. chain link fence) • Powder coating

17. The leaves are repelled by the like charge upon them.

18. 7.2 Electric Force--Summary • Force is a push or pull - electric force can doboth, without touching the object - it is anaction-at-a-distance force. Laws of Static Charge • Like charges repel • Opposite charges attract • Neutral objects areattracted to chargedobjects See pages 258 - 259

19. Charging Objects Charging By Conduction • Charging through direct contact • Extra electrons will move to a locationwhere there is less of them Charging By Induction • Bringing a charged object nearby a neutral object will cause chargemovement and separation in thein the neutral object • (like charges repel!) See pages 259 - 260