#### Transcript Document

```Simple Electric
Circuits
• Circuit Symbols
• Current
• Voltage
• Resistance
• Summary Table
Circuit Symbols
Identify the Circuit
Symbols
A Cell
A Filament
lamp/ Bulb
A Battery
of 2 Cells
A Switch
A Battery
of a number
of cells
A fixed
Resistor
Identify the Symbols
Variable
Resistor
L.D.R
Thermistor
Fuse
Heater
Loudspeaker
Identify the Circuit Symbols
A
V
M
Ammeter
Voltmeter
Motor
L.E.D
Draw the Circuit Symbols
Component
Circuit Symbol
Thermistor
L.D.R
Fuse
L.E.D
Current
Electrons Flow in the Opposite
way to the Conventional Current
-+
Electrons are
negatively
charged and
therefore flow
from negative
to positive
e-
We
normally
say that
the
current
flows
from
positive
to
negative
Current
Current is the FLOW
OF ELECTRONS
AROUND A CIRCUIT
In metals, current is
carried by electrons
The unit of
current is the
ampere (A)
We use an
ammeter to
measure current
Ampere
This is the
scientist AMPERE.
He studied current
in circuits and gave
his name to the
unit of current
Current in a Series Circuit
2A
2A
2A
The Current in a Series Circuit
is the Same at Every Point
In a series circuit the bulbs
are all the same brightness
If the
bulbs are
of the
same
rating!
Current Questions
A
B
C
1) The current reading for bulb B is 2A. What
are the readings for bulbs A and C?
2) Bulb suddenly fails. What happens to bulbs
A and C?
What Is the Current at This
Point?
6A
Brightness of Bulbs in a
Series Circuit
If a cell is added
the current will
increase and the
bulb gets brighter
Brightness of Bulbs in a
Series Circuit
If a bulb is added the
current will decrease as
there is greater
resistance in the circuit
and the bulbs get dimmer
Current in a Parallel Circuit
A PARALLEL circuit has more than one path
for the current to flow through
Bulb A
Bulb B
Assuming both bulbs
are the Same…they
will be the same
brightness
Current in a Parallel
Circuit
The Advantages of a
parallel circuit are:
Bulb A
Bulb B
• If one bulb fails
….the other will remain
on
• Both bulbs can be
switched on separately
Current in a Parallel Circuit
6A
2A
2A
2A
6A
The total
flow of
current is
equal to the
total
current
from all of
the
branches
What is the ammeter reading?
9A
3A
3A
3A
Voltage (Potential
Difference)
Voltage Is the Driving Force That
Pushes the Current Around the
Circuit
We need Energy to
push the electrons
around the circuit.
In this case the
energy comes from
the lemon (in the form
of chemical energy)
Potential Difference/ Voltage
This is VOLTA. He
studied the driving
force that pushes
current around a
circuit. He gave his
name to the unit of
Potential Difference
The unit of Potential Difference is
the VOLT (V)
Voltage in a Series Circuit
12V
4V
4V
12V
4V
The voltage in a
series circuit is
shared across
each
component. The
sum of the
voltages across
each component
equals the
source voltage
What Is the Voltage?
?V
8V
8V
?V
8V
6V
6V
6V
Voltage in a
Parallel
Circuit
The voltage is
the same
across all
components in
parallel
9V
What Is the
Voltage?
?V
?V
Resistance
Resistance
Resistance is anything in a
circuit that restricts the
flow of current
It can be calculated using Ohm’s Law:
Resistance
=
(Ohms)
The unit of
Resistance is the
Ohm
Voltage (V)
V
Current (A)
I
x
R
Complete the meter readings
6A
12V
A2
A3
V1
A1
V2
V3
Calculate the resistance
?
12V
3A
Current-Voltage Graphs
Show Resistance
A Resistor
at constant
temperature
I
V
Different wires
have different
resistances
The current through a
resistor at constant
temperature is proportional
to the voltage
Current-Voltage Graphs
Show Resistance
I
V
A Filament
Bulb
As the temperature
of the filament
increases, the
resistance increases –
hence the curve
Current-Voltage Graphs
Show Resistance
Current will only flow
through in ONE
DIRECTION
I
V
A Diode
(It has very high
resistance in the
reverse direction)
Resistance in Wires – Cross
Sectional Area
Thin wires have more resistance than
thick wires
Halving the cross sectional area of a
wire doubles its resistance because
there is half as much space for the
electrons to move
Resistance - Length of Wire
Doubling the Length of a
wire Doubles its
resistance because the
electrons have twice as
far to move
Resistance - Material
Different materials have different
resistances.
For Example: A nichrome wire has
more resistance than a copper wire
of the same size (the atoms in
nichrome hold the electrons more
tightly than copper atoms)
Dark
1A
The Light Dependent
Resistor
Light
5A
The resistance of the LDR depends on
the amount of light falling on it. Its
resistance decreases as the amount of
light falling on it increases
The Thermistor
1A
COLD
5A
WARM
The resistance of a thermistor depends
on its temperature.
Its resistance decreases as the
temperature of the thermistor increases
Explain Fully How the
Following Work
1) A Diode
2) A Thermistor
3) A Light Dependent Resistor
Summary: Current,
Voltage, Resistance,
Series & Parallel
How are voltmeters & Ammeter
connected in a circuit?
A
Ammeters
are always
connected
in SERIES
Voltmeters
are always
connected in
Parallel
V
Summary Table
Current
Is the flow of electrons
around a circuit
Voltage
Is the driving force that
pushes the current
around.
Is anything in a circuit
which slows the flow
down
Resistance
There is a Balance….
If you increase the Voltage –
then more current will flow
If you increases the Resistance
– then less current will flow
Which Is the Series and
Parallel Circuit
A * Current is THE SAME at any point
* Voltage SPLITS UP over each component
B
* Current SPLITS UP down each branch
* Voltage is THE SAME across each branch