1. Section 20.1 Electric Charge and Static Electricity p. 600
Ch Electricity
Section 20.1
Electric Charge and Static Electricity
p. 600 1 1

2. Electric Charge Causes subatomic particles to attract/repel 2 types
+ and –
Everything affected by charge

3. Neutral atom = protons & e-’s
Gain e-’s = - ion
Lose e-’s = + ion
Excess/shortage of e-’s produce net charge
Coulomb (C) - SI unit of electric charge
6.24 x 1018 e-’s = 1 C

4. Electric Forces Opposite charges attract
Electric force depends on charge & distance
2x distance = ¼ electric force
Stronger than gravity
Hold atoms together

5. Electric Fields The effect electric charge has on other charges
Strength depends on amt of charge producing field & distance from charge
Exerts forces on charged object placed in field.
More net charge object has, greater force on it

6. Static Electricity and Charging
net accumulation of electric charges on an object
Charge can be transferred by
Friction
Contact
Induction

7. Static Electricity and Charging
During charge transfer, total charge same before & after transfer
Law of conservation of charge

8. Charging by friction e-’s move from hair to balloon
Atoms in rubber >attraction for e-’s
Balloon net – charge
Hair net + charge
- -
+ + +

9. Charging by contact
Touch electrically charged object – you become charged
Sphere still has net charge, but reduced
Van de Graaff generator

10. Charging by Induction Transfer of charge w/o contact btwn materials
Walk across carpet
Pick up extra e-’s; net – charge
Repels e-’s in doorknob
Leaves net + charge on doorknob closest to hand
Doorknob overall charge neutral, but charges moved within it

11. Static Discharge Occurs when pathway forms for charges to move
Air becomes charged when hand near doorknob
Air provides path for e-’s

12. Static Discharge – lightning
Charge built up from friction btwn moving air masses in clouds
- charge in bottom of cloud induces + charge in ground
Charge in cloud increases
Attraction increases
Air charged – pathway for e-’s
Lightning 5:06

13. Electric Current and Ohm’s Law p. 604
Chapter 20.2
Electric Current and Ohm’s Law
p. 604

14. Electric Current Continuous flow of electric charge
SI unit is ampere, or amp (A)
2 types:
Direct current (DC)
Alternating current (AC)

15. Direct Current Charge flows in 1 direction
Most battery opperated devices
Flashlights
Remotes

16. Alternating Current Current that regularly reverses its direction
Electric current in homes, businesses, & schools often use AC

17. Electric current in a flashlight
e-’s flow from - to + terminal
Current in opposite direction!
Scientists define current as direction + charges flow

18. Conductors material that allows e-’s to flow easily
Metals like copper and silver
Made of ions in a lattice
ions - atoms that gained or lost e-’s
Ions not free to move
Each ion has e-’s loosely held
Free e-’s conduct charge

19. Insulators material that doesn’t allow e-’s to move through it easily
e- are tightly held
ex: plastic, wood, rubber, glass

20. Resistance e-’s in electric curent collide opposes flow of e-’s
Tungsten - high resistance
e-’s in electric curent collide
opposes flow of e-’s
electrical energy converted to thermal energy & light
measured in ohms ()
Thickness, length, temp affect resistance

21. Resistance depends on.. wire thickness
more resistance in thinner wires
milkshake in thin v.s. thick straw
wire length
more resistance in longer wires
Temp
high resistance at high temps
e-’s collide more often

22. Superconductors Can resistance ever be 0?
Superconductors produce near zero resistance when cooled to low temps.

23. Voltage Potential Difference (voltage)
diff in electrical potential btwn 2 places in electric field
Similar to PE diff of water at top and bottom of fountain
large separation of charge creates high voltage
Large fountain – high PE
“push” causing e- to move from - to +
measured volts (V)

24. Voltage sources
Fountains pump water to top, voltage source increases PE of electric charges
batteries
solar cells
generators

25. Ohm’s Law increasing voltage increases current
Increasing resistance decreases current

26. A lightbulb with a resistance of 160  is plugged into a 120-V outlet
A lightbulb with a resistance of 160  is plugged into a 120-V outlet. What is the current flowing through the bulb? I V R
GIVEN:
R = 160 
V = 120 V
I = ?

27. Electroscope Electroscope
instrument that detects presence of electrical charges
leaves separate when they gain + or - charge