Electric Current and circuits

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Transcript Electric Current and circuits

Electric Current and Circuits
Direct Current
 Direct
Current: A flow of charge that
ALWAYS flows in one direction.
A battery – The terminals are + and - .
Electrons always move through the
terminals in the same direction. They
move from negative to positive.
 Ex.
Alternating Current
 Electrons
in the circuit move first in one
direction and then in the opposite
direction. (Alternating back & forth)
 This
is done by alternating the “polarity” at
the voltage source.
 Buildings
including homes use alternating
current at 120 volts
Electric Current (I)
 Depends
on voltage(V) and resistance(R)
Current is measured in amps(A)
 Voltage is measured in volts(V)
 Resistance is measured in ohms(Ω)
Ohm’s Law : describes the relationship
between voltage, current and resistance
V = IR

Electric Power
 The
rate at which electrical energy is
converted to Mechanical energy, heat or
light is Electric Power.
 The electrical energy comes from power
stations that use electromechanical
generators powered by heat engines
fueled by burning coal, falling water, wind
or nuclear power to make
electricity.
Formula to calculate POWER
 Electric
Power = current x voltage
 UNITS-1 watt = 1 ampere x 1 volt
 Ex.
Calculate how much power is
used by a calculator that operates on
8 V and 0.1 A.
 Power
= current x voltage
P
= (I) (V)
P
= (0.1A) (8V)
P
= 0.8 W
 Ex.
Will a 1200-watt hair dryer
operate on a 120-volt line if the
current is limited to 15 amperes by a
safety fuse?
 How
many watts can the circuit
provide?
P
= IV
 P = 15A x 120V
 P = 1800 watts
 YES
! It can run !!
Electric Circuits
 There
must be a complete path from the
positive terminal of the battery to the
negative terminal of the battery
 Any path along which electrons can flow is
a circuit
 It must be continuous
Two Types of circuits
 Series—from
a single pathway for electron
flow
 Parallel—from branches, each of which is
a separate path for the flow of electrons
 Series
Parallel
Series circuit
 Single
pathway for current to flow
 Current is resisted by each device and the
sum is the total resistance of the pathway
 Current = voltage/resistance
 Total voltage divides among each device
 If one device fails,
 the circuit fails to function
Parallel circuit
 Each
device has its own pathway from one
terminal to the other
 Voltage is same across each device
 Total current divides amongst the
branches
 Total circuit is sum of the current in the
branches
 As branches increases,
resistance decreases
Schematic diagrams
 Simple
diagrams to describe electric
circuits
 Zig zag line shows resistance and
resistance free wires are solid lines