1. Charge & Electricity
Unit 6 – Lecture 1

2. Review 3 types of subatomic particles protons: + charged
neutrons: non-charged
electrons: - charge
Equal p+ & e- = neutral atom or compound
Objects with no net charge are called neutral

3. Charge Charge – a point source of electrical force
two types – positive and negative
opposite charges attract
like charges repel
most objects are neutral

4. Conservation of Charge
Law of Conservation of Charge
charges are neither created nor destroyed, they can only be transferred from one object to another

5. Review
“Sea of Electrons” – elements in a metallic bond do not hold their electrons tightly, but share them between all atoms

6. Static Charge
static electricity – the accumu- lation of excess electric [negative] charge on an object
static = not in physical motion
“static cling” – objects that are oppositely charged “stick” together

7. Static Charge
static electricity – the accumulation of excess electric [negative] charge on an object
electrons are being transferred from the carpet to your shoe
electrical discharge – sudden and momentary electric current between two objects

8. Static Charge Lightening is a form of static discharge
static charges are formed when the particles inside the storm cloud rub against each other [because of convection], separating charges.

10. Electric Field
area around a charged object which exerts forces on other electric charges

11. Review Conductor a material through which electrons can move easily
best are metals [sea of electrons]

12. Review
Insulator
a material through which electrons are not able to move easily
plastic, wood, rubber, glass…etc

13. Charging Objects Charge by Contact
transfer of charge by direct touch or rubbing
static cling

14. Charging Objects Charge by Induction
rearrangement of electrons in a neutral object because of a charge from a nearby object

15. Electricity
Electric Current [I]– the net movement of electric charges in a single direction
ex: spark between you and doorknob
measured in Amperes [A]
1 A = 6,250 million billion electrons per second passing a single point

16. Electricity Volt (V) – unit of the PE of an electrical charge
electricity flows from that of higher voltage to lower voltage

17. Resistance
Resistance [R] – a material’s opposition to the flow of current
measured in Ohms (Ω)
resistance will turn electrical E into thermal E and light

18. Resistance
Resistance [R] – a material’s opposition to the flow of current
conductor – less resistance
insulator – more resistance

19. Resistance Increase resistance with… increase temperature
increase length
decrease thickness

20. Resistance Decrease resistance with… more, smaller batteries
shorter, thicker wire
more conductive metal

21. V I R Electricity Ohm’s Law: Current = Voltage / Resistance I = V / R
Voltage = Current * Resistance
V = I * R
Resistance = Voltage / Current
R = V / I V I R

22. P V I Electricity Power (W) is measured in Watts
Power = Voltage * Current
Watts = Volts * Amps
P = V * I P V I

23. Practice
The current in a clothes dryer is 15 A when plugged into a 240 V outlet. How much electrical power does the clothes dryer use?
3,600 watts OR 3.6 kilowatts
Calculate the voltage difference in a circuit with a resistance of 50 Ω if the current of the circuit is 0.7 A.
35 volts

24. Electricity
Electrical Energy is measured in kilowatt hours [kWh]
Electrical Energy = Electric Power * time
E = P * t
A microwave oven with a power rating of 1,200 W is being used for 0.25 h. How much electri- cal energy is being used by the microwave?
0.30 kWh E P t

25. Homework
For ALL problems, show ALL work: Write Equation Plug In Numbers THEN Solve for Answer
ALL PROBLEMS MUST HAVE THESE THREE STEPS

26. Homework p 199 #s 6-7 p 212 #s 1-4 p 205 #s 6-7 p 213 #s 6-8