Transcript Current Electricity

Current Electricity
Chapter 22
22.1 Current & Circuits
 Society has become very dependant
upon electricity because of the ease in
which electricity is easily converted into
other forms of energy
 Thermal, mechanical, light, sound, etc
Producing Electric Current
 What happens when a charged sphere
touches an uncharged sphere?
 The one had a high potential than the
other and the charges flow until there is
no potential difference between the two
sphere
Current
 The flow of charged particles is an
electric current
 Charge flows from higher potential to
lower potential
 The flow of positive charge is called
conventional current
 The flow stops when the potential
difference is zero
 To maintain the flow of current a
difference in potential must be
maintained by pumping charged
particles back to the higher potential
 Many devices are used to do the
pumping like a dry cell
 A combination of dry cells is called a
battery
Electric Circuits
 A closed loop or conducting path that
allows the charges to flow is called an
electric circuit
 Includes a pump to increase the
potential difference and a device to
reduce the potential difference, light
bulb etc…
 The potential energy lost by the
charges, qV, is usually converted into
some other type of energy
Conservation of Charge
 Charges cannot be created or
destroyed, but they can be separated
 The total amount of charge doesn’t
change
 Energy is also conserved
 E=qV (Change in electrical energy)
 Because q is conserved the net change
in potential energy around the circuit
must be zero
 Thus, the increase in potential
difference produced by the battery must
be equal to the decrease in potential
difference across the load
 If the potential difference between two
wires is 120 V, the load must do 120 J
of work on each coulomb of charge that
is delivered
Rates of Charge Flow & Energy Transfer
 Power is rate at which energy is
transferred into other forms of energy,
watt (W)
 If a generator transfers 1 J of KE to
electric energy each second then the
power is 1 W.
 The electrical energy depends upon the
charge transferred and the potential
difference
 E=qV
 The rate of flow of charge is call electric
current, q/t
 Symbolized by I
 Coulombs/second or Ampere, A
 E=qV
E qV
P 
 IV
t
t
Resistance & Ohm’s Law
 Resistance-the opposition to the flow of
electric current
 Copper very low resistance glass very
high resistance
 Resistance is the ratio of the electric
potential difference, V, to the Current, I
V
R
I
 Resistance is measured in Ohms, 
 Named after Georg Simon Ohm who
found the ratio of potential difference to
current is constant for a given conductor
 Most metallic conductors obey Ohm’s
law over a limited range of voltages
 But many devices don’t obey Ohm’s law
 Transistors, diodes, even a light bulb
that varies in resistance with
temperature
 Resistors are devices used to control
the current or voltage supplied to a
circuit
Diagramming Circuits
 Know the symbols
Types of meters
 Voltmeter-measures potential difference
across a circuit or device
 Connected in parallel
 Ammeter-measures current through a
circuit or device
 Connected in series