1. Static and Current Electricity
Advanced Physical Science

2. Static Electricity
Static Electricity = electric charge at REST on an object
remember static means not moving
If something has static electricity, it means there an EXCESS or LACK of electrons (e-)
Examples:
Clothes clinging when removed from dryer
Lightning (before the strike)
Your charged finger after walking on carpet

3. The Atom Normally, atoms are electrically neutral
Each atom has the same number of electrons (negative) as protons (positive)
Electrons are whirling about, far away from the nucleus and can be removed from the atom by FRICTION!

4. Charge by FRICTION
When certain materials are rubbed together, electrons are transferred from 1 surface to another.
The blue balloon rubbed against sweater is charged
Excess e- = Negative Charge
Lack of e- = Positive Charge
Like charges repel
Unlike charges attract

5. Charge by Conduction
Conduction =e- move from 1 object to another by DIRECT CONTACT
Charging an electroscope shows conduction
Electroscope
After charging, the metal leaves have same charge and repel

6. Charge by induction
Charges in an uncharged object are rearranged without direct contact with the object
The negative charges on the yellow balloon make a section of the wall have a positive charge.
Electrons in the wall are
repelled by and move away
from the balloon

7. Induction Example 2 Lightning
The negative charge at the bottom of the cloud INDUCES a positive charge on the ground

8. Static Discharge
When a surface has acquired a strong negative charge, the extra e- may jump to a neutral or positive object
The “jump” of e- gives a spark
Spark= a rapid movement of a # of e- through the air
Ex: lightning

9. Current Electricity
Current electricity is the flow of electric charges through a wire or other conductor. Current flows from high voltage to low voltage. Current only occurs when there is a difference in voltage. Current flows from positive to negative.

10. More about Current
Current: the flow of electrons through a conductor. Current is measured in amperes (amps or A) Symbol used for current in equations is I. Why “I”? Originally current was referred to as electrical Intensity by French scientist, André-Marie Ampère. Measured using an ammeter

11. Notes - continued
Two types of electric current: AC & DC – No, this is not the rock band!! AC – alternating current – the electrons are changing direction rapidly. (household current – in U.S. current alternates 120 times per second) DC – direct current – the electrons flow in only one direction (ex. = battery)

12. Important Terms
Current: the flow of electrons through a conductor. Conductor: a material through which electric charges can flow. Resistance: opposition to the flow of electrons

13. Notes about Resistance
Resistance (R) is measured in ohms. Named for Georg Ohm – German scientist who developed mathematical descriptions of electrical circuits. The symbol for ohms = Ω (Greek letter omega) A light bulb offers resistance to flow of e- Your skin also offers resistance to flow of e- Wet skin offers less resistance than dry OR

14. More on Resistance Resistance depends on:
Thickness and/or length of the wire
Thicker wire = less resistance
How well the material conducts electric current
Temperature
In general for metals, as temperature increases, resistance increases (direct relationship)

15. Voltage
Voltage: Push that causes electric charges to flow Also known as potential difference Electrons flow from high potential to low potential The difference in voltage is what drives the current through a resistor

16. More about Voltage
Without voltage, there will be no electric current. Voltage is measured in volts (V) Measured using a voltmeter

17. Ohm’s Law
I = Current (amps or A) V = Voltage (volts of V) R = Resistance (ohms or Ω) Instead of learning different formulas for current, voltage and electricity, you can use this single formula to find ANY of them Use Ohm’s Law Triangle to solve

18. Reminders about Circuits
There are 2 Types of Circuits: Series – one path for the electrons to travel If one light goes out, they all go out. 

19. Circuits (Cont)
Parallel – more than one path for the electrons to travel If one light goes out, the remainder of the lights remain lit. Don’t you hope your house is wired this way?

20. Play with Circuits http://www.andythelwell.com/blobz/

21. Use Ohm’s Law in a Circuit
Given that you have a 12 volt battery and a lightbulb that offers 3 ohms (Ω) of resistance, what is the amount of current (I) going through the wire?
Solve…
12V = I*3 Ω
I = 12V/3 Ω
I = 4 amps

22. Electrical Power
Rate at which electrical energy is converted to other forms of energy. Measured in watts. Formula: P = Power V = Voltage I = Current

23. Electric Energy
Electric energy = P = power (in kilowatts) T = time in hours Electric energy is measured in kilowatt hours. 1 kWh = 1000 watts of power for 1 hour of time Convert watts to kilowatts by dividing by 1000 (dimensional analysis) Ex: 220 watts * 1 kilowatt/1000 watts = 0.22 kW

24. Calculating Electrical Energy Cost
From the HW the other night…
A room was lighted with three 100 watt bulbs for 5 hrs per day. If the cost of electricity was $0.09 per kWh, how much would be saved by switching to 60 watt bulbs?
Step 1: You are using 3 bulbs, so figure out how many watts in 3 bulbs
100 watts*3 = 300 watts
60 watts*3= 180 watts

25. Calculating Energy Cost (cont)
Comparing 300 watts vs 180 watts
Step 2: Convert 300 watt and 180 watt to kilowatt (divide by 1000)
300 watt * 1 kilowatt/1000 watt = 0.3 kW
180 w * 1 kw/1000 w = 0.18 kW
Step 3: Find the difference in kW used
0.3 kW kW = 0.12 kW

26. Calculating Energy Cost (cont)
Step 4: determine energy by multiplying by the hours used
0.12 kW * 5 h= 0.6 kWh
Step 5: What is the cost? $0.09 per kWh
0.6 kWh * $0.09/kWh= $0.054 or 5.4 (5) cents