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Electric Charge Current

• Chapter 20

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Types of Electric Charge

• What are the two types of charge?
• Positive
• Negative
• Ben Franklin named these charges.
• Where do these charges come from?
• Protons
• Electrons

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Interactions Between Charges
4
Electric Field

• Region around a charged particle where a force is
  exerted.
• Similar to magnetic field
• Draw with lines to show what kind of force would
  be on a test charge (always )
• Remember, what is a force?

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Electric Fields around Single Charge
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Electric Fields AroundMultiple Charges
7
Static Charge

• What is the charge of most objects?
• Trick question??
• Most objects are neutral.
• What does that mean?
• Protons equal Electrons or -

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So, how do things become charged?

• Can all materials become charged?
• Insulators electrons cannot be lost easily
• Conductors electrons free to move
• Electrons can be lost or gained.
• Less electrons means
• Less negative or a overall positive charge
• More electrons means
• More negative or a overall negative charge

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Static Electricity

• A buildup of charges on an object is called
  Static Electricity.
• Charges buildup but do not flow.

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Transferring Charge

• Conduction
• Charge transfer through direct contact
• 2. Induction
• Movement of electrons to one part of an object
  caused by the electric field of another object

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Conservation of Charge

• Charges (electrons) are not created or destroyed
• So, if one object gains electrons another object
  must have lost electrons
• And, if one object loses electrons another object
  must have gained electrons

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Static Cling

• Why does your sock stick to your shirt?
• Its all about charges, opposites attract.
• Why does a dryer sheet help reduce this?
• When might static cling be beneficial?

13
Static Discharge

• When a negatively charged object and a positively
  object are brought together, electrons move until
  both objects have the same charge.
• The loss of static electricity as electric
  charges move off an object is called static
  discharge.

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How can static discharge?

• Humidity
• Water in the air can pick up charge that has
  built up on an object.
• Sparks
• Shock, electrons moving from hand to door knob
  results in neutral objects again.
• Lightning
• Electrons buildup on clouds then discharge to
  areas of positive charge.

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Detecting Charge

• Electric charge is invisible, but it can be
  detected by a special instrument called a
  Electroscope.
• Uncharged metal leaves hang straight
• Charged metal leaves repel

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Circuit Measurements
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Electrical Potential

• An object will move from a place of high
  potential energy to a place of low potential
  energy.
• What would be an example of this?
• Electrons will also move from high potential to
  low potential energy exerted by an electric
  field.
• Potential energy per unit of charge is called
  electrical potential.

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Voltage

• The difference in electrical potential between
  two places is called the potential difference.
• This provides the force that pushes the charge
  through a circuit.
• Voltage is the unit for electrical difference.
• Voltage causes current to flow through an
  electric circuit.

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Voltage Sources

• Creates a potential difference.
• Batteries and generators
• Just as an increase in the difference in height
  causes a greater flow of water, an increase in
  voltage causes a greater flow of electric
  current.

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Resistance

• Opposition to the flow of charge.
• Depends on the type of wire, thickness, and
  length.
• Current depends on resistance.
• The greater the resistance, the less current
  there is for a given voltage.
• Path of least resistance

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Ohms Law

• Voltmeter measures potential difference
• Ammeter measures current
• Ohms Law VIR
• VoltageCurrent x Resistance
• VoltsAmps x Ohms

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Series Parallel Circuits
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Series Circuits

• Only one path for the current to take
• All parts of circuit connected one after the
  other.
• Added resistors (light bulbs) decreases current
• Ammeter connected in series.

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Parallel Circuit

• Several pathways for current to flow
• Each resistor connect to energy source separately
  
• Each pathway can have different current going
  through it
• Voltmeter is connected in parallel

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Household Circuits

• Would you want your house to be series or
  parallel?
• Why?

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Electrical Safety
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Becoming Part of a Circuit

• Short circuit a connection that allows current
  to flow through an unintended path
• Exposed Wires
• Resisting Current

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Grounding

• Third Prong
• Lightning Rods
• A lightning rod is connected to a grounding wire.
  When lightning strikes the rod, charges flow
  through the rod, into the wire, and then into
  Earth.

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Fuses Circuit Breakers

• In order to prevent circuits from overheating,
  devices called fuses and circuit breakers are
  added to circuits.
• A fuse is a device that contains a thin strip of
  metal that will melt if too much current flows
  through it.
• A circuit breaker is a safety device that uses an
  electromagnet to shut off the circuit when the
  current gets too high.

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Electric Shocks

• Current in the body
• The severity of an electric shock depends on the
  current.
• .1 to .2 amps can be dangerous
• Resistance in the body
• Dry skin High resistance
• Wet skin Low resistance