Download Circuits

Electric Circuits
An electrical device that provides a path
for electric current to flow.
Previously, we studied electrostatics,
which is the study of charges at rest.
Now we’ll begin to focus on electric
currents within circuits, which involve
charges in motion.
What Things Are Common to
All Circuits???
• Every circuit must have a
continuous path through which
electrons may move.
• Must have a potential
difference or voltage to cause
the electrons to move.
• Each circuit should have some
circuit loads, such as resistor, to
utilize electrical energy.
• NO load could result in a short
circuit.
Circuit Diagrams & Symbols
There are two basic types of
circuits:
One is known as a series
circuit which has only one path
for the electrons to flow through.
The second type of known
as a parallel circuit because
there are two or more paths
for the electrons to travel
through.
NOTICE:
Three
closed
loops or
circuit
‘branches’.
Which resistors are in Series?
Which resistors are in Parallel?
B
Series: R2, R3 and R4
Parallel: R1 and R3
Electric Current
A current (I) exists when charge moves or
“flows” through a region. Current is the rate of
charge flow past a point in an electric circuit per
unit time.
Q
I
t
The magnitude of the current is measured in
amperes (A), where 1 A = 1 C/s.
Conventional Current
The direction of conventional current is in
the direction in which positive charge
flows. In reality, it is the electrons that
move.
6.0 
I
6V
For electric charge to move, there
must be a complete path or closed
circuit.
Switches
open and
close
circuits
Which switches must be closed for
bulb A to light?
Which switches must be closed
for bulb B to light?
Bulb A:
Switches a & c
Bulb B:
Switches a & b
Fuses and Circuit Breakers are two
electrical safety devices designed to open
the circuit when too much current flows.
A short circuit occurs when
excessive current overloads a
circuit, causing device failure
and potentially fire.
Current can change
direction
Two different types of current :
Direct currents (DC) and
alternating currents (AC).
In a direct circuit, the current flows in only one
direction. Ex: Batteries
In an alternating current, the direction
of the current changes, reversing
direction of flow at a particular
frequency. Ex: Plugs and outlets
DC vs AC
Direct Current
Power Source
Alternating
Current Power
Source
A potential difference is necessary within a
circuit to get electrons to move.
Voltage (V): electromotive force or
potential difference, usually expressed in volts.
As voltage increases, current increases.
Batteries
• Batteries, known as
electrochemical cells or dry cells,
are common circuit elements
that provide this necessary
potential difference, by
converting chemical energy into
electrical energy.
• Car Battery- wet cell
• Rechargeable batteries reverse
the process, converting electric to
chemical for reuse.
Electric Resistance (R)
When charge flows through a circuit, it encounters
resistance or opposition to flow.
The resistance of a metal
conductor is a property which
depends upon its dimensions,
material and temperature.
As resistance increases, current decreases.
Resistance is measured
in Ohms ().
Ohm’s Law
The magnitude of the electric current that flows
through a closed circuit depends directly on the
voltage and inversely on the circuit resistance.
Units:
Current (I)
Amps
Voltage (V)
Volts
Resistance (R)
ohms, 
Using Ohm’s Law
D
R=2
C
A Simple
Circuit
i=?
A
B
V=6V
V 6V
I 
 3A
R 2Ω
Electrical Power is the rate at which
energy is used.
The units for power are J/s or Watt
(W).
•
•
•
•
Power (Power) – Watts
Voltage (V) – Volts
Current (I) – amps
Resistance (R) - ohms
• Power (P) – Watts
• Work (W) - Joules
• Time (t) – seconds
Circuit Construction
• Circuit Construction Simulator:
http://phet.colorado.edu/en/simulation/circuitconstruction-kit-dc