#### 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
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
```