Chapter 7 :
Electricity and Magnetism
Section 2 : Electric Current
Connecting Concepts
• We studied:
1) Exothermic Reactions
2) Energy transformations
3) Electric Charges
Energy Transformation and Batteries
• Inside the battery, a series of exothermic
chemical reactions take place.
• Chemical Energy is transformed into
Electrical Energy
• The connection between the - and +
terminals of batteries triggers the chemical
reactions and the electrons will flow from the
– terminal to the + terminal.
• The flow of e- is called Electric Current
What is an electric current?
Electric current is the flow of electric charges
( electrons).
Electrons will move along a wire, or a battery
• It is a continuous
movement.
Electric Current can be measured
• Electric Current is measured in a SI unit
called Ampere. (A)
• Ampere is the amount of charges that flow
in and out of the wire in one second.
• In one second, about six billion charges flow
into and out of the wire
Electric Current can be measured
• An ammeter is an instrument used to
measure the flow of an electric current
Electric Circuit
• When you watch TV,
you need the TV to
keep functioning
continually so you can
watch an entire show.
• You need electrons
flowing non stop
generating enough
electricity to power the
TV.
You need Electric Circuits!
• Electric Circuits are a closed path in which
electric charges can flow without
interruption.
***Why are circuits important?
• Electrical Circuits provide means of
transferring electrical energy from
sources such as batteries or other
generators, to devices that will transform
these energy into light ( light bulb,
television), heat ( electric heater),
sound ( radio or television).
*A force must be exerted on electric
charges to make them flow.
Where is this force coming from?
From Electric Fields.
All charged objects have an electric
field that surrounds.
In a battery: The (-) and (+) terminals of the
battery produce an electric field.
The electric field exerts force on the electrons.
This force causes the electrons to have electrical
energy and flow.
Electrons flow from the negative to the positive
terminal of the battery.
EX of an Electric Circuit :
You need: a battery, a bulb and a switch to
make electrons flow.
For the electrons to flow, the switch needs to be
closed.
• When you
turn on a light
by flipping a
switch, you
are closing
the circuit.
• The electric
current will
flow and the
light will turn
on.
Simple, Series and Parallel Circuits
• Electric Circuits are a closed path in
which electric charges can flow without
interruption.
• There are three types of circuit:
Simple, Series and Parallel Circuits
• 1)In a simple circuit, there is only one light
bulb and only one closed path for the
current to flow.
• 2)In a series circuit, there are more than
one light bulb that are connected so there is
only one closed path for the current to
follow.
• If any part of this path is broken, current
will no longer flow in the circuit.
Simple Circuit
only one lamp – one path
Series Circuit
more than one bulb – one path
3)Parallel Circuits
• In a parallel circuit, devices are connected
so there is more than one closed path for
current to follow.
• If the current flow is broken in one path,
current will continue to flow in the other paths.
• That is what happens when you have only one
light on in your house..
• Classroom lights are another example – we can
have only one on and the other off.
Parallel Circuit
Drawing of a circuit x Circuit Diagram
Electric Resistance
• + and – charges
are constantly
colliding inside
the wire.
• this cause
electrons to
change direction,
creating
resistance to the
flow..
Electric Resistance
• The measure of how difficult it is for
electrons to flow in an object is called the
electric resistance of the object.
• The unit for electric resistance is the ohm,
symbolized by Ω ( omega – Greek letter)
In what type of material there will be less resistance?
Insulators or Conductors?
**Why are resistors important?
**Resistors: fight current flow by using up
some of the energy in the flow.
So a resistor is used to lower and to control
the flow of electrons.
EX: If you have a 12 volt battery and a 9 volt
lamp, the lamp will 'blow' pretty quickly.
A resistor will drop the 3 extra volts.
If you have a flow of charges too high for your
circuit, you can lower it by adding a resistor.
Voltage
• **Voltage measures the amount of energy
that will be carried by the electrical charges
in a circuit.
• The higher the voltage, the higher will be
the electric energy that will flow.
• Ampere is the amount of charges that flow
in and out of the wire in one second.
• The voltage between two points in a circuit
can be measured with a voltmeter.
• The SI unit for Voltage is the volt (V)