Download Electric Current

Electric Current – SPH 3U1
Consider the structure of the atom:

The centre is called the
___________________

It contains the _______________(+)
and ___________________ (0)

The outer rings are called
________________ which contain
the _________________ ( - )
Only the electrons are able to move from atom to atom so their motion is the foundation
of ELECTRIC CURRENT.
Electric Current: the amount of charge that passes a given point in a conductor per
second
Symbol:
Unit:
Formula:
We don’t count the number of electrons passing a point because that value would
simply be too BIG. We group electrons into units of charge called COULOMBS
where:
1 C = 6.24x1018 electrons
Example: A light bulb with a current of 0.80A is left radiating for 45 minutes. How much
electric charge passes through the filament of the light bulb?
How many electrons passed through the bulb?
An ammeter is used to measure electric current. To use an ammeter, it must be
connected as part of the electric circuit loop so that the electrons go through the meter.
Electric Potential Difference – SPH 3U1
Because electric charges exert forces of attraction or repulsion on each other, we can
consider how much force would be needed to move an electric charge from one point to
another while feeling an electric force from another charged particle.
Electric Potential Difference: the work done to move a charged object through an
electric field (essentially it is the amount of work per unit charge). Electric potential
energy is converted into another useful form of energy.
Symbol:
Unit:
Formula:
Example: The current flowing through a flashlight bulb is 0.50A and the potential
difference across the filament is 2.4V. How much work is done in moving the charge in
2.0s?
Example: It takes a current of 10A for 300s to boil a kettle of water requiring 3.6x10 5J of
heat energy, what is the potential difference across the kettle’s heating element?
A voltmeter is used to measure the electric potential difference between two points in
an electric circuit. The voltmeter must be connected across these two points and is
therefore NOT part of the original electric circuit.
Electrical Resistance – SPH 3U1
As electrons are travelling through a circuit, they will lose energy as their motion is
resisted by the atoms that they are travelling across. This is called electrical
resistance.
Symbol:
Unit:
Formula:
Example: Find the resistance of an electric light bulb if there is a current of 0.8A when
the potential difference across the bulb is 120V?
Example: What is the potential difference across a toaster of resistance 13.7Ω when the
current through it is 8.75A?
Electric Circuits and Symbols
Component
Symbol
Component
Symbol
Cell
resistor
Voltmeter
fuse
Connecting wires
crossing wires
Ammeter
light
Switch
ground
Battery
capacitor
The Four Parts of a Simple Circuit:
Diagram:
1.
2.
3.
4.
Direction of Electron Flow
Since the wires are made of conductors, the electrons in the metal wires can ___________ from
atom to atom. The negatively charged electrons are going to be ___________________ by the
negative terminal of the energy source and ____________________to the positive terminal of the
energy source.
Current flow is actually defined as being ___________________ to electron flow!
Series vs. Parallel Circuits
Series Circuits: electrons must pass through ___________ __________________ in the circuit
before returning to the ______________
Example:
Parallel Circuits: the electrons reach a point where they can follow _______________ or another
so they do not have to pass through _________ ________________ in a circuit before returning to
the source
Example:
Combining Resistors
In Series:
R1
R2
R3
𝑹𝒕𝒐𝒕𝒂𝒍=
In Parallel:
R1
R2
R3
𝟏
𝑹𝒕𝒐𝒕𝒂𝒍
=
Kirchhoff’s Laws – SPH 3U1
Conservation of Energy: as electrons move through a _______________, they gain
________________ in sources and lose energy through ____________ but the total
amount of energy gained in one ___________ through a circuit is equal to the total amount
of energy ____________ in that loop.
Kirchhoff’s Voltage Law:
Around any complete ________________ in a circuit, the sum of the electric potential
increases is equal to the sum of the electric potential _______________________.
Mathematically:
Example:
Kirchhoff’s Current Law:
At any __________________ in a circuit, the total amount of electric current ___________
that junction is equal to the total amount of electric current ____________ that junction.
Mathematically:
Example:
Ohm’s Law:
The potential resistance across a conductor is directly proportional to the current flowing
through it.
Mathematically:
Circuit Analysis – SPH 3U1
In order to completely analyze a circuit, you must find all voltage, current and resistance values.
According to notation, I1 is the current flowing through resistor 1 and V1 is the potential
difference across resistor 1.
Example: Completely analyze the following circuit
R1=3Ω
R2=10 Ω
Vo = 10V
R3=10 Ω
R4 = 2 Ω
Step 1: simplify the circuit to find the total resistance
Step 2: Use Kirchhoff’s voltage law to find the current going through the source
Step 3: Determine where else that current flows and start finding all V’s, R’s and I’s