Electricity

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 cant 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
Warmup 12-1-11

• What is Electricity?
• What is a Positive Charge?
• What is Static Electricity?
• What is the Law of Conservation of Charge?

12
Electricity

• Transferring Electric Charge
• charge by contact the process of transferring
  charge by touching or rubbing

13
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

14
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

15
Electricity

• Lightning

16
Electricity

• Lightning

17
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

18
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.

19
Electricity

• The presence of electric charges can be detected
  by a device called an electroscope

20
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

21
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

22
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.

23
Electricity

• electric current the flow of electric charge
  through a wire or any conductor
• electric current is measured in amperes (A)

24
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)

25
Electricity

• Dry Cell Battery

26
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

27
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

28
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

29
Electricity

• Ohmss 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 ?)

30
Electricity

• Ohmss 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.