Electric Current

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Electric Current
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There are 72 names of French mathematicians,
engineers and scientists on the side of the
Eiffel tower
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Electric Current (I)

• The flow of electric charge
• Unit- Amperes (Symbol A)
• An Ampere - 1 coulomb of charge
• second
• (1 coulomb 6.24 billion billion electrons)
• Measured using an ammeter

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Electric Current

• When no electricity is appliedfree electrons
  (conducting electrons) are always moving in
  random motion

• But when the switch is closed the free
  electrons of the conductor are forced to drift
  toward the positive terminal under the influence
  of the electric field

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Resistance
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Resistance- helps to control the amt of current

• Opposition to the passage of an electric
  current through that conductor.
• Unit-  ohm (O)

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Resistance (R)

• The resistance of an object depends primarily on
  3 factors
• 1) What the material is made of
• Place in order of least resistance the following
  materials
• Aluminum, gold, silver,
• glass, copper

• Silver
• Copper
• Gold
• Aluminum
• Glass

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The resistance of an object depends primarily on
3 factors

• 2) Its thickness

• A thick copper wire has lower resistance than an
  otherwise-identical thin copper wire.

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Not a good idea

• 3) Its length

• For example- a long copper wire has higher
  resistance than a short copper wire. 

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Relationship between voltage, current and
resistance
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Ohms Law
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Ohms Law

• Current Voltage
• Resistance
• Current (amps) Voltage (volts)
• Resistance (ohms)
• The greater the voltage the _ the current
• The greater the resistance the _ the current

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Resistance

• A typical lightbulb has a resistance of 100 ?
• An iron or toaster has a resistance of 15-20 ?
• The lower resistance permits a large current,
  which produces a considerable amount of heat