Download Powepoint Chapter 20 Electricity

S-66
Students will investigate the properties of electricity and magnetism?
• Explain briefly where electricity comes
from.
Chapter 20
Electricity
SPS10 Students will investigate the properties of electricity and magnetism.
a.
Investigate static electricity in terms of –friction, induction, conduction
b.
Explain the flow of electrons in terms of
-alternating and direct current
-the relationship among voltage, resistance, and current
-simple series and parallel circuits
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?
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
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)
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)
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
protons and
caused by
electrons
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
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
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?
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
20.2 Electric Current and Ohm’s
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?
20.2 Current and Ohm’s 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
20.2 Current and Ohm’s 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
20.2 Current and Ohm’s 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
20.2 Current and Ohm’s 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)
20.2 Current and Ohm’s Law
How are voltage, current, and resistance related?
• Ohm’s Law – current is equal to potential
divided by resistance
V=IR
– V = potential difference in volts (V)
– I = current in amps (A)
– R = resistance in Ohm’s (W)
20.2 Current and Ohm’s 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?
V=98V
V=IR
V=(7A)(14W)
– Fill in the equation
– Answer
20.2 Current and Ohm’s 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?
I=1.25A
V=IR
120V=I(96W)
– Fill in the equation
– Answer
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?
S-69
What factors affect electrical resistance?
• What three factors determine the resistance
of an object?
• How does resistance change as each factor
changes?
20.3 Electric Circuits
What is included in a circuit diagram?
How do series and parallel circuits differ?
How do you calculate electric power?
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
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 don’t affect other devices
– Household circuits are parallel
20.2 Current and Ohm’s Law
How do you calculate electric power?
• Power is equal to voltage multiplied by
current
P=IV
– P = power in watts (W)
– I = current in amps (A)
– V = potential difference in volts (V)
20.2 Current and Ohm’s 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?
P=8160W
P=IV
P=(34A)(240W)
– Fill in the equation
– Answer
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