1. Chapter 7
Electricity

2. Electricity
An atom is the basic unit of matter and is made of protons, neutrons, & electrons
protons: + charge
electrons: - charge
neutrons: no charge

3. Electricity
An atom is the basic unit of matter and is made of protons, neutrons, & electrons
when atoms contain the same number of protons & electrons they have a neutral charge
positive charge – occurs when electrons are lost from atoms to other objects
negative charge – occurs when electrons are gained from atoms of other objects

4. Electricity
positive charge – occurs when electrons are lost from atoms to other objects
negative charge – occurs when electrons are gained from atoms of other objects

5. Electricity
static electricity – the accumulation of excess electric charges on an object
example: as you walk on carpet, some electrons that are loosely held by the carpet are transferred to your shoes creating opposite charges

6. Electricity
law of conservation of charge – states that charge can be transferred from object to object, but it can’t be created or destroyed
similar to the law of conservation of mass or the law of conservation of momentum

7. Electricity Like & Opposite Charges opposite charges attract
like charge repel

8. Electricity Conductors and Insulators
Electricity is caused by the movement of electrons, from a negative to a positive region
conductors - materials in which electrons can move through easily
examples: metals & water
responsible for shocks when an excess of electrons are transferred from one surface to another, such as from your hand to a doorknob

9. Electricity Conductors and Insulators
Electricity is caused by the movement of electrons, from a negative to a positive region 
insulators - materials in which electrons cannot move through easily
examples: wood, plastic, rubber, & glass

10. Electricity Transferring Electric Charge
charge by contact – the process of transferring charge by touching or rubbing
causes a transfer of electrons from one object to another, leaving one object with a positive charge and the other one with an equal amount of negative charge
example: socks being attracted to each other when coming out of the dryer because of rubbing during drying
touching a door handle and getting shocked

11. Electricity Transferring Electric Charge
charge by contact – the process of transferring charge by touching or rubbing

12. Electricity Transferring Electric Charge
charging by induction – rearranging of electrons on a neutral object caused by a nearby charged object
example: bringing a negatively charged balloon near clothing and having it cling to the clothing by an electrical force

13. Electricity Transferring Electric Charge
lightning - caused by a large static discharge of electrons through the air that meet with the positive charge that is built up on the ground
collisions of atoms and molecules in the air during
this discharge account for light being given off

14. Electricity
Lightning

15. Electricity
Lightning

16. Electricity Transferring Electric Charge
4. thunder - sound wave generated by lighting
the heat from lightning causes air to expand rapidly,
producing sounds waves that you hear as thunder

17. Electricity
grounding – a way to transfer any excess electric charge to the ground before it builds up and creates lightning
examples: lightning rods, pipes, plumbing fixtures, metal faucets, etc.

18. Electricity
The presence of electric charges can be detected by a device called an electroscope

19. Electricity 7.2: Electric Current
How is it that electrons can move from one object to another or move through an object? The answer lies with a difference in voltage

20. Electricity
voltage difference – the push that causes electrical charges to flow through a conductor
measured in volts (v)
Just how heat moves from a high temperature area to a lower temperature area, charge flows from a high voltage area to a low voltage area

21. Electricity
circuit – closed, conducting loop through which an electric current can flow
If the circuit is not closed, the electrons would have nowhere to go, just as if a water line broke, the water would not be able to flow through the pipe.

22. Electricity
electric current – the flow of electric charge through a wire or any conductor
electric current is measured in amperes (A)

23. Electricity Types of Batteries
dry cell - involves a chemical reaction between zinc and a chemical paste that cause the central carbon rod to become positive and the surrounding lower region to become negative
once the two terminals are connected through a circuit, electricity flows
these types of batteries are the most common type (in flashlights or calculators)

24. Electricity
Dry Cell Battery

25. Electricity Types of Batteries
wet cell - involves two metal plates and typically an acid solution with a “bridge”
these types of batteries are used in cars

26. Electricity
resistance – the tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light
resistance means, how hard it is to get electricity through
resistance in measured in ohms ()
all materials have some electrical resistance
electrical conductors have much less resistance than insulators

27. Electricity
resistance – the tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light
list some factors that affect resistance in a wire
Material of the wire, length of the wire, and thickness of the wire

28. Electricity
Ohms’s Law – a formula that is used to measure the amount of voltage or current in a circuit
V = I  R
V: voltage (measured in V)
I: current (measured in amps)
R: resistance (measured in )

29. Electricity
Ohms’s Law – a formula that is used to measure the amount of voltage or current in a circuit
V = I  R 
Calculate the voltage difference across a 25- resistor if a 0.3-amp current is flowing through it.