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ELECTRICITY!
SO, YOU ARE CONFUSED ABOUT
ELECTRICITY?
HERE ARE THE BASICS…
CIRCUITS
•
An electric circuit is like a pathway made of wires that electrons can flow through. A
battery or other power source gives the force (voltage) that makes the electrons
move. When the electrons get to a device like a light bulb, your computer, or a
refrigerator (these devices are called loads), they give it the power to make it work.
•
The word “circuit” sounds like “circle,” and a circuit needs to be circular to work. The
wires have to go from the power source to the device and back again, so that the
electrons can go out and come back.
•
Many circuits have a switch so that they can be turned on and off. When the switch is
off, it makes a gap in the circuit and the electrons are not able to flow around a
complete circle. When the switch is turned on, it closes the gap and the electricity is
able to move and make the device work.
SERIES CIRCUIT
• A series circuit is a circuit where there is only one path from the source through
all of the resistors and back to the source. This means that all of the current in
the circuit must flow through all of the resistors.
• Voltage is split between all loads (like lightbulbs), Current remains the same.
SERIES CIRCUIT
• All resistors are in a single circle (series circuit).
• The voltage supplied by the power source is
divided equally to each resistor.
• Notice how the series circuit with one lightbulb is
much brighter than the series circuit with three
lightbulbs. This is because the one lightbulbs
receives all available voltage, but the three
lightbulbs each get only 1/3 of the available
voltage.
SERIES CIRCUIT
• This is a diagram of a series circuit.
• How many resistors do you see?
• How will the voltage be affected?
• How will the current be affected?
SERIES CIRCUIT
• This is a diagram of a series circuit.
• How many resistors do you see?
four
• How will the voltage be affected?
Each resistor will get ¼ of the
voltage provided by the battery
• How will the current be affected?
Current remains constant in the circuit
PARALLEL CURCUIT
• Two or more electrical devices in a circuit can be connected by series connections or
by parallel connections. In a parallel circuit, each device is placed in its own separate
circle. When you have multiple circles it means that there are multiple pathways by
which charge can travel in the circuit. Each charge passes through one circle of the
circuit, and therefore through a single resistor present in the circle. When arriving at
the branching location, a charge makes a choice as to which branch to travel through
on its journey back to the power source.
• Each load gets the full voltage from each charge, but the current is divided by the
number of pathways that are available (charges take the path of least resistance).
PARALLEL CURCUIT
• How many resistors do you see?
• How is the voltage affected?
• How is the current affected?
PARALLEL CURCUIT
•
How many resistors do you see?
Three
•
How is the voltage affected?
Each resistor receives the total about
of voltage supplied by the battery
because each charge only passes
through one resistor.
•
How is the current affected?
Each charge chooses one pathway to
travel, so current is divided by the
number of pathways in the circuit.
INCREASE ENERGY
• To increase the brightness of a bulb, the amount of energy per second, or
power, delivered to the bulb needs to increase. This can be done by either
increasing the amount of energy carried by each charge (the voltage of the
battery), or by increasing the rate at which the charges go around the circuit
(increasing the current), or by increasing both the voltage (energy per charge)
and the current (charge/second).
CIRCUITS
• How does a circuit work?
• How do electric charges move around in a circuit?
• How does increased voltage change the amount of energy?
• How does increasing the current change the amount of energy?
CIRCUITS
•
How does a circuit work? In an electric circuit the charge carries energy, supplies it to devices, and
then gets more energy, but the amount of charge does not change. Charge is conserved in a
circuit.
•
How do electric charges move around in a circuit? A conductor’s outermost electrons are easy to
move between atoms. These outermost electrons are known as free electrons. They are bound to
the group of metal atoms in a kind of “sea of electrons” but not connected to any particular single
atom. When they flow from atom to atom, we call it “electricity.” Electrons will flow like this only
when there is a complete loop or circuit (circle) for them to travel through.
•
How does increased voltage change the amount of energy? When you increase the voltage, you
increase the amount of energy each charge carries
•
How does increasing the current change the amount of energy? When you increase the current,
you increase the amount of energy to a load per second.
CHARGES
• Energy is transferred from the battery to the charges and then from the
charges to the different resistors in the circuit, such as light bulbs and fans.
• Some energy gets transferred into heating of the circuit. The moving charges
transfer all their energy in the circuit before they return to the battery. No
charges are lost. The charge remains constant in the circuit.
CHARGE
• The particles that carry charge through wires in
a circuit are the free electrons. These
negatively charged electrons move from the
negative direction to the positive direction. They
only move when there is an electric field in the
circuit, in other words, when the circuit is complete
(complete circle).
RESISTANCE
• Resistance is when the current is slowed down in a circuit.
• A load is a device that uses the electricity that flows through it, and changes it
into another form of energy like light or motion. Examples would be
lightbulbs, refrigerators, motors, etc.
• All loads are resistors, but not all resistors are loads. Example: changing the
thickness of a wire can change the rate of flow (current), but it does not
transform the energy into a new form of energy.
VOLTAGE
• We define voltage as the amount of potential energy between two points on a
circuit. One point has more charge than another. This difference in charge
between the two points is called voltage. It is measured in volts, which,
technically, is the potential energy difference between two points that will give
one joule of energy per coulomb of charge that passes through it
• The unit “volt” is named after the Italian physicist Alessandro Volta who
invented the first chemical battery. Voltage is represented in equations by the
letter “V”.
VOLTAGE
•
When describing voltage, current, and resistance, a
common analogy is a water tank. In this analogy, charge
is represented by the water amount, voltage is
represented by the water pressure, and current is
represented by the water flow. So for this analogy,
remember:
•
Water = Charge
•
Pressure = Voltage
• Flow = Current
• Consider a water tank at a certain height above the ground. At
the bottom of this tank there is a hose.
VOLTAGE
• The pressure at the end of the hose can represent voltage. The
water in the tank represents charge. The more water in the tank,
the higher the charge, the more pressure is measured at the end
of the hose.
• We can think of this tank as a battery, a place where we store
a certain amount of energy and then release it. If we drain our
tank a certain amount, the pressure created at the end of the
hose goes down. We can think of this as decreasing voltage,
like when a flashlight gets dimmer as the batteries run down.
There is also a decrease in the amount of water that will flow
through the hose. Less pressure means less water is flowing,
which is less current.
CURRENT
•
The rate at which charge flows through a circuit is known as the current. Charge does
NOT pile up and begin to accumulate at any given location such that the current at
one location is more than at other locations. Charge does NOT become used up by
resistors in such a manner that there is less current at one location compared to
another. In a parallel circuit, charge divides up into separate branches such that there
can be more current in one branch than there is in another. Nonetheless, when taken
as a whole, the total amount of current in all the branches when added together is
the same as the amount of current at locations outside the branches. The rule
that current is everywhere the same still works, only with a twist. The current outside
the branches is the same as the sum of the current in the individual branches. It is still
the same amount of current, only split up into more than one pathway.
POWER
• Power is a measure of how much work can be performed in a given amount of
time. Work is generally defined in terms of the lifting of a weight against the
pull of gravity. The heavier the weight and/or the higher it is lifted, the more
work has been done. Power is a measure of how rapidly a standard amount
of work is done.
POWER
•
In electric circuits, power is a function of both voltage and current.
P=IxE
•
Power (P) is exactly equal to current (I) multiplied by voltage (E), When using this
formula, the unit of measurement for power is the watt (W).
•
Neither voltage nor current by themselves constitute power. Power is the combination
of both voltage and current in a circuit. Remember that voltage is the specific work
(or potential energy) per unit charge, while current is the rate at which electric
charges move through a conductor. Voltage (specific work) is similar to the work done
in lifting a weight against the pull of gravity. Current (rate) is similar to the speed at
which that weight is lifted. Together as a product (multiplication), voltage (work) and
current (rate) constitute power.
OHM’S LAW
• Combining the elements of voltage, current, and resistance, Ohm developed the
formula:
V=IxR
Where
• V = Voltage in volts
• I = Current in amps
• R = Resistance in ohms
FORCE
• The force that makes electrons move is a voltage, or potential difference. The
force is produced by an imbalance of electric charge.
VOCABULARY
• Electricity is energy due to electric charges. It can be static (charges don’t move)
or dynamic (charges move).
• Current is the rate that charges move by a given point or cross section, given in
Amperes or Coulombs/second
• Voltage is the potential energy per charge, also called the electric potential,
measured in volts. 1 V = 1 Joule/Coulomb
• Resistor is an electronic device that resists electric current (the resistance is
measured in Ohms.)
VOCABULARY
• Power is the rate at which energy is used, measured in watts.
1 Watt = 1
Joule/second
• Electric Potential is the voltage or the potential energy per charge
• Charge is a property of matter. Electrons have a negative charge of 1 6 10 19 . × −
C. One Coulomb of charge is composed of 6 25 1018 . × electrons.