Electric and Magnetic Phenomena

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Electric and Magnetic Phenomena

• 5. Electric and magnetic phenomena are related
  and have many practical applications. As a basis
  for understanding this concept

Standard 5
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• 1. Static electricity is a part of life. Can you
  name at least five examples of static electricity
  that occur in your home?
• 2. Fabric softeners are commonly used today
  because they eliminate static cling. Explain why
  clothes in the dryer get static cling.

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• 3. Why can walking across a carpeted room be a
  shocking experience?
• 4. Magnets have both north and south poles. While
  like poles repel each other, opposite poles
  attract each other. Explain the parallelism
  between magnetism and electric charge.

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Electricity

• Electric Charge and Force

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Electric Charge

• Electrical property of matter
• Creates a force between objects
• Positive or Negative

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Electric Charge

• Opposite charges
• Attract

• Like charges
• Repel

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3.

• The electric force between charged objects isc.
  either attractive or repulsive.

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Electrical Charge

• Depends on the imbalance of electrons and protons
• Protons positive
• Electrons negative
• Neutron neutral
• Leads to a net charge

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• 2. When there is an equal amount of positive and
  negative charges on an object, the object is
• c. neutral.

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Coulomb

• SI unit for charge
• Proton 1.6 x 10-19 C
• Electron -1.6 x 10-19C
• Charges are equal and opposite

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Flow of Charge

• Conductor
• Material that transfers charge easily

• Insulator
• Material that does not transfers charge easily

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Charging by Contact

• Electrons move from the rod to the doorknob

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Charging by Contact

• Transfer of electrons
• Gives the doorknob a negative charge

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Induced Charges

• Induces a positive charge near the rod
• Induces a negative charge away from the rod

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Induced Charges
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i. Students know

• plasmas, the fourth state of matter, contain ions
  or free electrons or both and conduct
  electricity.

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Charging by Friction

• When rubbed together electrons can be transferred
  from one material to the other
• material that gets the electrons becomes
  negatively charged
• material that loses the electrons becomes
  positively charged

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Electric Force

• The force of attraction or repulsion between
  objects
• Due to charge
• Without electric force life would be impossible
• Depends on charge and distance

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Electric Force

• Proportional to the product of the charges
• Inversely proportional to the distance between
  them squared
• Equation F q1 q2 /4peo r2

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e. Students know

• charged particles are sources of electric fields
  and are subject to the forces of the electric
  fields from other charges.

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Electric Field

• Produced around charged particles
• Other charged objects around will experience an
  electric force
• Electric force acts through electric fields

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• 4. Every charged particle produces
• d. an electric field.

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Point Charges

• Electric field lines point in the direction of
  the electric force on a positive charge

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Point Charges

• Positive is attracted to negative
• Electric Field lines point inward

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Electric Field Lines

• Show direction of electric force
• Also show relative strength

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Electric Fields
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Electric Fields
In the figure shown, why do only half of the
lines originating from the positive charge
terminate on the negative charge?
Because the positive charge is twice as great as
the negative charge.
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Electric Force

• varies depending on
• charge and distance between charged objects

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Students know

1. how to predict the voltage or current in simple
   direct current (DC) electric circuits constructed
   from batteries, wires, resistors, and capacitors.

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b. Students know

• how to solve problems involving Ohms law.

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c. Students know

• any resistive element in a DC circuit dissipates
  energy, which heats the resistor. Students can
  calculate the power (rate of energy dissipation)
  in any resistive circuit element by using the
  formula Power IR (potential difference) x I
  (current) I 2 R.

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d. Students know

• the properties of transistors and the role of
  transistors in electric circuits.

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Electrical Potential Energy

• Potential energy of charged object
• Due to its position in electric field

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• 16. What determines the electrical potential
  energy of a charge? _____________
• Determined by the position of the charge relative
  to all the other electrical charges

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Electrical Potential Energy
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Potential Difference

• Change in the electrical potential energy per
  unit charge
• Measured in Joule / Coulomb
• 1 J/C 1 volt or 1V or voltage

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Volts

• Measure of potential difference
• Terminals of a battery have a potential
  difference
• Cell (battery)
• Source of current
• Voltage across the terminals

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Dry Cell and Car Battery
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Batteries

• Typically have one positive and one negative
  terminal.

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Current

• Voltage sets charges in motion
• Current Rate of electric charges moving through
  a conductor
• ?1 C/s 1 ampere or 1 amp

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Electric Current

• Produced when charges are accelerated by an
  electric field
• Charges move to a position of potential energy
  that is lower

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7.

• Current is the rate at which charges move through
  a(n)a. conductor. b. insulator. 

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Electrical Resistance

• What is the voltage from the wall?
• 120 V
• What is the power of a bulb?
• 40W, 60W, 100W

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• 5. Resistance is caused byinternal friction. 6.
  The SI unit of resistance is thec. ohm.

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Electrical Resistance

• Causes changes in current
• Caused by internal friction
• Slows the movement of charges
• through collisions
• Collisions can cause material to heat up

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Electrical Resistance(Ohms Law)

• Resistance voltage/current
• R V / I
• ? V / A
• ? Ohm

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Resistance

• A set of electric trains is powered by a 9 V
  battery. What is the resistance of the trains if
  they draw 3.0 A of current?
• Answer 3 ?

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Resistance

• A battery-operated CD player uses 12 V from the
  wall socket and draws a current of 2.5 A.
  Calculate the resistance of the CD player.

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Resistance

• There is a potential difference of 12 V across a
  resistor with 0.25 A of current in it. The
  resistance of the resistor is
• Answer 48?

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Ohms Law

• A light bulb has a resistance of 12 ?. It is
  attached to a battery that has a voltage of 24 V.
  Calculate the current in the light bulb.
• Answer 2 A

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Current

• A resistor has a resistance of 280?. How much
  current is in the resistor if there is a
  potential difference of 120 V across the
  resistor?
• Answer 0.43 A

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17.

• A resistor has a resistance of 1.8-ohm. How much
  current is in the resistor if there is a
  potential difference of 3.0 V across the
  resistor?
• Answer 1.67 A 

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9.

• A 13-ohm resistor has 0.050 A of current in it.
  What is the potential difference across the
  resistor?
• Answer 0.65 V 

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Series Circuits
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Series Circuits
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Parallel Circuits
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Parallel Circuits
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18.

• Which bulb(s) will have a current in the
  schematic diagram above?
• Only the first light bulb will light. The other
  two bulbs are beyond the open switch and
  therefore, will not receive current.

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19.

• Does the schematic diagram above represent a
  series or parallel circuit?
• Answer series circuit

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19.

• Does the schematic diagram above represent a
  series or parallel circuit?

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18.

• Is a current flowing in the schematic diagram
  above? Explain your answer.

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• 10. What happens to the resistance of a
  superconductor when its temperature drops below
  the critical temperature?
• Answer Resistance drops to zero.

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Electric Energy

• Energy associated with electrical charges
• Whether moving or at rest

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Electrical Power

• Rate at which electrical energy is used in a
  circuit
• power current x voltage
• P IV
• 1 Watt 1 Amp x 1 Volt

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• A color television draws about 2.5 A when it is
  connected to a 120 V outlet. Assuming electrical
  energy costs 0.060 per kWh, what is the cost of
  running the television for exactly 8 hours?
• Answer 0.14

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8.

• A flashlight bulb with a potential difference of
  4.5 V across its filament has a power output of
  8.0 W. How much current is in the bulb filament?
• Answer 1.8 A 

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Household Circuits
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• 7. What is the potential difference across a
  resistor that dissipates 5.00 W of power and has
  a current of 5.0 A?
• Answer 1.00 V

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11.

• If a lamp is measured to have a resistance of
  120-? when it operates at a power of 120 W, what
  is the potential difference across the lamp?
• Answer 120 V

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12.

• A microwave draws 5.0 A when it is connected to a
  120 V outlet. If electrical energy cost
  0.090/kWh, what is the cost of running the
  microwave for exactly 6 hours?
• Answer 0.32

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13.

• What happens to the overall resistance of a
  circuit when too many appliances are connected
  across a 120 V outlet?
• Answer Resistance is decreased.

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11.

• An electric toaster has a power rating of 1100 W
  at 110 V. What is the resistance of the heating
  coil?
• Answer 11? 

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13.

• A device that protects a circuit from current
  overload is called a(n)
• Answer circuit breaker.

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14.

• What is charging by contact?

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16.

• A 180-ohm resistor has 0.10 A of current in it.
  What is the potential difference across the
  resistor?
• Answer 18 V

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Study Guide

• Attraction, repulsion
• Electric force
• Batteries
• Current, potential
• Resistance
• Ohms law VIR

• Power, P VI
• Circuits, parallel, series
• Charge/ing,
• Electric fields
• Conductor, insulator