1. Unit 4: Electromagnetism

2. Announcements No test corrections Lowest test grade will be dropped
Homework: EdPuzzle video will be posted and due tonight (deadlines will be at midnight the night of the lesson so students have the option of watching before class or after)

6. Unit 4: Electromagnetism

7. Charging Things Up
Elementary Charge

8. Atomic Structure Review
Matter is made up of small structures called ATOMS
Within the NUCLEUS are two types of NUCLEONS
At the center of each atom is a NUCLEUS
Orbiting the NUCLEUS are ELECTRONS
ELECTRONS
NEGATIVE charge
Orbit nucleus
PROTONS
NEUTRONS
POSITIVE CHARGE
DO NOT MOVE
WITHIN MATTER
NO CHARGE – NEUTRAL
DO NOT MOVE
WITHIN MATTER

9. Definitions charge: a fundamental property of matter
measured in COULOMBS or ELEMENTARY CHARGE
charge on an object is carried by particles
Electron
-1.6 x coulombs
-1e
Proton
+1.6 x coulombs
+1e

10. + - Charged Objects Objects are normally electrically NEUTRAL.
They have the same number of protons and electrons
If an object loses electrons, it
becomes
POSITIVELY charged
If an object gains electrons, it
becomes
NEGATIVELY charged + -
LACK OF ELECTRONS
EXCESS ELECTRONS

11. This plate is neutral – number of protons = number of electrons
Charged Objects
Because objects can only gain or lose electrons, the only charges that are allowed are multiples of the ELEMENTARY CHARGE
This plate is neutral – number of protons = number of electrons
If the plate loses two electrons
If the plate loses one electron
If the plate loses three electrons
Its charge becomes…
Its charge becomes…
Its charge becomes…
+3 e Or
+4.8 x Coulombs
+2 e Or
+3.2 x Coulombs
+1e Or
+1.6 x Coulombs
The plate has a LACK OF ELECTRONS
+3 Elementary Charges
+1 Elementary Charge
+2 Elementary Charges

12. Example #1 An object has three excess electrons.
What is its “elementary charge”?
What is its charge in coulombs (converting)?
-3e
q = -3e x (1.6 x C)/1e = x C

13. Example #2 An object has 75 protons and 65 electrons
What is its “elementary charge”?
What is its charge in coulombs?
+10 e
q = +10e x (1.6 x C)/1e = +16 x C

14. Law of Conservation of Charge
The total amount of charge in a closed system remains constant – charge is not created or destroyed, it only moves from one object to another
Charge “moves” as a result of ELECTRON movement ONLY!!!

15. The TOTAL CHARGE remains the SAME!!!
Example #3
A metal sphere with two excess electrons touches a neutral metal sphere and then taken away.
What do you predict the charge on each sphere will be after they make contact?
What is the total charge on both spheres after they come in contact?
-1e or -1.6 x C
-2e or -3.2 x C
The TOTAL CHARGE remains the SAME!!!

16. Practice Which charges could NOT exist in a real-world object?
(a) 3.2 x C (e) 0.5 x C
(b) 6.5 C (f) 3.2 x C
(c) -20 e (g) 3.5 e
(d) 1.2 x 102 e (h) 1.6 x e
Object A begins with a charge of -3.0 coulombs; object B begins with a charge of -7.0 coulombs; and object C begins with no charge. Object A is touched to object B then removed. Object B is then touched to object C and removed. What is the final charge on each of the three objects?

17. Practice
Which charges could NOT exist in a real-world object? (a) 3.2 x C (e) 0.5 x C (b) 6.5 C (f) 3.2 x C (c) -20 e (g) 3.5 e (d) 1.2 x 102 e (h) 1.6 x e [e, f, g, h – easiest way is to convert to elementary charge first] Object A begins with a charge of -3.0 coulombs; object B begins with a charge of -7.0 coulombs; and object C begins with no charge. Object A is touched to object B then removed. Object B is then touched to object C and removed. What is the final charge on each of the three objects? [A = -5C, B = -2.5C, C = -2.5C]

18. Going over Packet Problems