Unit Electricity

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Unit Electricity

• I. Electric Charge
• Static Electricity
• Conductors
• Insulators
• Electroscope

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What do these have in common?
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A. Static Electricity

• Static Electricity
• the net accumulation of electric charges on an
  object
• Electric Field
• force exerted by an e- on anything that has an
  electric charge
• opposite charges attract
• like charges repel

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A. Static Electricity

• Static Discharge
• the movement of electrons to relieve a separation
  in charge

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B. Conductors

• Conductor
• material that allows electrons to move through it
  easily
• e- are loosely held
• ex metals like copper and silver

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C. Insulators

• Insulator
• material that doesnt allow electrons to move
  through it easily
• e- are tightly held
• ex plastic, wood, rubber, glass

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D. Electroscope

• Electroscope
• instrument that detects the presence of
  electrical charges
• leaves separate when they gain either a or -
  charge

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• II. Electric Current
• Circuit
• Potential Difference
• Current
• Resistance
• Ohms Law

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Potential Difference
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B. Potential Difference

• Potential Difference (voltage)
• difference in electrical potential between two
  places
• large separation of charge creates high voltage
• the push that causes e- to move from - to
• measured in volts (V)

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C. Current

• Current
• flow of electrons through a conductor
• depends on of e- passing a point in a given
  time
• measured in amperes (A)

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D. Resistance

• Resistance
• opposition to the flow of electrons
• electrical energy is converted to thermal energy
  light
• measured in ohms (?)

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Resistance

• Caused by internal friction in conductor and
  slows the movement of charges.
• A 40 W light bulb is dim and has a higher
  resistance than a bright 100W light bulb.

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• https//www.youtube.com/watch?vKvVTh3ak5dQ
• Resistance video

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D. Resistance

• Resistance depends on
• the conductor

• wire thickness
• less resistance in thicker wires

• wire length
• less resistance in shorter wires
• temp - less resistance at low temps

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E. Ohms Law

• Ohms Law

V potential difference (V) I current
(A) R resistance (?)
V I R

• Voltage increases when current increases.
• Voltage decreases when resistance increases.

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E. Ohms Law

• A lightbulb with a resistance of 160 ? is plugged
  into a 120-V outlet. What is the current flowing
  through the bulb?

KNOWN/UNKNOWN R 160 ? V 120 V I ?
EQUATION I V R
WORK I (120 V) (160 ?) I 0.75 A
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Superconductors
Some metals have zero resistance when their
temperature falls below a certain temperature
(critical temperature). The range is from -458º
F to -189ºF.
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• III. Electrical Circuits
• Circuit components
• Series circuits
• Parallel circuits
• Household circuits

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• https//www.youtube.com/watch?vl8JS8BbrVOg
• Video
• https//www.youtube.com/watch?vlYZUXV-v71Y

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• https//www.youtube.com/watch?vD2monVkCkX4
• Circuits

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A. Circuit

• Circuit
• closed path through which electrons can flow

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A. Circuit Components

• A - battery C - light bulb
• B - switch D - resistor

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B. Series Circuits

• Series Circuit
• current travels in a single path
• one break stops the flow of current
• current is the same throughout circuit
• lights are equal brightness
• each device receives a fraction of the total
  voltage
• get dimmer as lights are added

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C. Parallel Circuits

• Parallel Circuits
• current travels in multiple paths
• one break doesnt stop flow
• current varies in different branches
• takes path of least resistance
• bigger light would be dimmer
• each device receives the total voltage
• no change when lights are added

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D. Household Circuits

• Combination of parallel circuits
• too many devices can cause wires to overheat
• Safety Features
• fuse - metal melts, breaking circuit
• circuit breaker - bimetallic strip bends when
  hot, breaking circuit

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• IV. Measuring Electricity
• Electrical Power
• Electrical Energy

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A. Electrical Power

• Electrical Power
• rate at which electrical energy is converted to
  another form of energy

P power (W) I current (A) V potential
difference (V)
P I V
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A. Electrical Power

• A calculator has a 0.01-A current flowing through
  it. It operates with a potential difference of 9
  V. How much power does it use?

KNOWN/UNKNOWN I 0.01 A V 9 V P ?
EQUATION P I V
EQUATION P (0.01 A) (9 V) P 0.09 W
P
V
I
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B. Electrical Energy

• Electrical Energy
• energy use of an appliance depends on power
  required and time used

E energy (kWh) P power (kW) t time (h)
E P t
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B. Electrical Energy

• A refrigerator is a major user of electrical
  power. If it uses 700 W and runs 10 hours each
  day, how much energy (in kWh) is used in one day?

UNKNOWN/KNOWN P 700 W 0.7 kW t 10 h E ?
WORK E P t E (0.7 kW) (10 h) E 7 kWh
EQUATION E P t
E
t
P