Explain briefly where electricity comes from.

1
S-66 Students will investigate the properties of
electricity and magnetism?

• Explain briefly where electricity comes from.

2
Chapter 20 Electricity

• SPS10 Students will investigate the properties of
  electricity and magnetism.
• Investigate static electricity in terms of
  friction, induction, conduction
• Explain the flow of electrons in terms of
• -alternating and direct current
• -the relationship among voltage, resistance, and
  current
• -simple series and parallel circuits

3
20.1 Electric Charge and Static Electricity

• What produces a net electric charge?
• What determines whether an electric force is
  attractive or repulsive?
• What determines the strength of an electric
  field.
• What are three ways in which charge is
  transferred.
• How does static discharge occur?

4
20.1 Charge and Statics What produces a net
electric charge?

• Electric Charge a property that causes protons
  and electrons to attract or repel each other
• Two types
• Positive - protons
• Negative electrons
• An excess or shortage of electrons causes atoms
  to be charged
• That causes objects to be charged

5
20.1 Charge and Statics What determines whether
an electric force is attractive or repulsive?

• Electric Force force of attraction or
  repulsion between electrically charged
  objects
• Like charges repel (positve-positive,
  or negative-negative)
• Opposite charges attract
  (negative-positive)

6
20.1 Charge and Statics What determines the
strength of an electric field?

• Electric Field the space around a charged
  particle where it will push or pull another
  charge
• Depends on
• Amount of charge
• Distance from the charge
• Drops off rapidly (square of the
  distance)

7
20.1 Charge and Statics What are the three ways
in which charge is transfered?

• Static Electricity charges that are not moving
• Law of conservation of charge the total amount
  of charge stays the same
• Remember that charge is caused by
  protons and electrons

8
20.1 Charge and Statics What are the three ways
in which charge is transfered?

• There are three ways that charge is transffered
• Friction
• Two uncharge objects rub against each other
• Electrons are pulled off one object and placed on
  the other
• Contact
• A charged object comes in contact with an
  uncharged object
• The charged object loses charge until they both
  have the same charge

9
20.1 Charge and Statics What are the three ways
in which charge is transfered?

• There are three ways that charge is transffered
• Induction
• Electrons in an object are attracted or
  repelled by a charge
• This causes a temporary charge in a
  neutral object

10
S-67 Students will investigate the properties of
electricity and magnetism?

• What are the two types of charges?
• What are the two basic charged particles?
• How does a charge form?

11
20.1 Charge and Statics How does static discharge
occur?

• Electrons will flow if there is a conducting
  pathway
• Static discharge when a pathway between charged
  objects is formed
• Shocking yourself on a doorknob
• Lighting bolt

12
20.2 Electric Current and Ohms Law

• What are the two types of current?
• What are some examples of conductors and
  insulators?
• What factors affect electrical resistance?
• What causes and electric current?
• How are voltage, current, and resistance related?

13
20.2 Current and Ohms Law What are the two types
of current?

• Electric Current the flow of charge
• Two types
• Direct Current
• Flows in only one direction
• Electricity from batteries
• Alternating current
• Changes direction in a regular pattern
• Has frequency (usually 60 Hz)
• Household electricity

14
20.2 Current and Ohms Law What are some examples
of conductors and insulators?

• Electrical conductor material that charge flows
  through easily
• Metals
• Graphite
• Salt solutions
• Electrical insulator material that charge does
  not flow through easily
• Plastics
• Rubber

15
20.2 Current and Ohms Law What factors affect
electrical resistance?

• Resistance opposition to the flow of charge
• Resistors use up the energy in electricity
• Measured in Ohm (W)
• Three factors affect resistance
• Thickness thicker objects have less resistance
• Lenth longer objects have more resistance
• Temperature resistance increases with
  temperature

16
20.2 Current and Ohms Law What causes an
electric current?

• Voltage (Potential Difference) difference in
  potential energy between two points
• Units are volts (V)
• Produced by sources of electric energy
• A potential difference placed across a loop of
  conductor will result in a current
• Current is measured in Amperes or Amps (A)

17
20.2 Current and Ohms Law How are voltage,
current, and resistance related?

• Ohms Law current is equal to potential divided
  by resistance
• V potential difference in volts (V)
• I current in amps (A)
• R resistance in Ohms (W)

VIR
18
20.2 Current and Ohms Law How are voltage,
current, and resistance related?

• What is the potential difference that would allow
  a 7 A current to flow through a 14 W toaster?
• Fill in the equation
• Answer

VIR
V98V
V(7A)(14W)
19
20.2 Current and Ohms Law How are voltage,
current, and resistance related?

• How much current would flow through a 96 W light
  bulb when it is plugged into a 120 V source?
• Fill in the equation
• Answer

VIR
I1.25A
120VI(96W)
20
S-68 How are voltage, current, and resistance
related?

• A toaster is plugged into a 120 V wall outlet.
  How much current will it draw if it is a 47 W
  resistor?

21
S-69 What factors affect electrical resistance?

• What three factors determine the resistance of an
  object?
• How does resistance change as each factor changes?

22
20.3 Electric Circuits

• What is included in a circuit diagram?
• How do series and parallel circuits differ?
• How do you calculate electric power?

23
20.3 Electric Circuits What is included in a
circuit diagram?

• Electric Circuit complete pathway
• Circuit diagram show the path and devices in
  the pathway
• Common symbols are
• Battery
• Battery of cells
• Resistor
• Light bulb
• Switch

24
20.3 Electric Circuits How do series and parallel
circuits differ?

• Series Circuit
• Has only one pathway for current
• If one device is disconnected they all stop
  working
• Parallel Circuit
• Has more than one pathway for current
• Devices dont affect other devices
• Household circuits are parallel

25
20.2 Current and Ohms Law How do you calculate
electric power?

• Power is equal to voltage multiplied by current
• P power in watts (W)
• I current in amps (A)
• V potential difference in volts (V)

PIV
26
20.2 Current and Ohms Law How do you calculate
power?

• An electric oven is connected to a 240 V line,
  and it uses 34 amps of current. What is the
  power used by the oven?
• Fill in the equation
• Answer

PIV
P(34A)(240W)
P8160W
27
S-70 How do you calculate power?

• How much power would a hair dryer use if it draws
  15A of current when plugged into a 120V wall
  socket?
• Hair dryer boring
• Powerful tank - cool