Electricity1 Electric and Magnetic Phenomena 5. Electric and magnetic phenomena are related and have many practical applications. As a basis for understanding.

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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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Electrical Charge

• Depends on the imbalance of electrons and protonso Protons = positiveo Electrons = negativeo Neutron = neutral

• Leads to a net charge

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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

• Conductoro Material that

transfers charge easily

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

the rod

Induced Charges

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Induced Charges

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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 /[4o r2 ]

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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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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

Because the positive charge is twice as great as the negative charge.

In the figure shown, why do only half of the lines originating from the positive charge terminate on the negative charge?

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Electric Force

• varies depending on

• charge and distance between charged objects

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Electrical Potential Energy

• Potential energy of charged object

• Due to its position in electric field

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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)

o Source of currento 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 conductor1 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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Electrical Resistance

• What is the voltage from the wall? o 120 V

• What is the power of a bulb?

40W, 60W, 100W

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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(Ohm’s 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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Series Circuits

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Series Circuits

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Parallel Circuits

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Parallel Circuits

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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 GuideAttraction, repulsion• Electric force• Batteries • Current, potential• Resistance• Ohm’s law: V=IR

• Power, P = VI• Circuits, parallel,

series• Charge/ing, • Electric fields• Conductor,

insulator