Download Electrical Energy and Circuits

Electrical Energy,
Electric Power and Circuits
Colleyville Heritage High School
Mr. W. Puckett
Electric Current
 The
opposite of electrostatics is
electric current; the flow of electric
charges like electrons.
 We get electric current from wall
sockets primarily.
 It is made with generators at electric
generation plants.
Why Would Electrons Move in
Electric Current ?

Electricity is the movement of electrons.
 Why would it move?
 Because an outside force pushes it.
 The pressure / force that pushes electrons in
electricity is the electric field Potential
Energy. We call this pressure VOLTAGE
 The electric generator pushes the charges
with voltage. Much like water is pushed
with a pump.
Electric Current Analogy to
Hydrology
A good example is to compare the flow of
water in a hose to electric flow.
 The amount of water flow is equal to the
current.
 The water pressure is equal to voltage
potential.
 The resistance is the backpressure due to
either the diameter of the hose or a squiring
handle nozzle that regulates water flow.

Potential
Electricity can be
described like
flowing water.
Current
Load
Example of Using Water to get
Work Done that compares to
Electricity
The turning wheel make
corn kernels into corn
meal for cooking.

Gris Mills use water to turn
the wheel to grind the grain.
Flowing charge is called current. The
symbol is I and the unit is the ampere or
amp (A).
SIM
Electrical Current
The net amount of electric charge that
passes through a circuit is called the
Electric Current (I) and is described by the
equation: I = DQ / Dt where Q is the
amount of charge and t is time.
 The scientific unit for current is the
Ampere (A) and is equal to the flow of 1
Coulomb per second.

Charge flows
in an Electric
Circuit.
Switch
Charge is a quantity of electricity.
Charge has the unit coulomb (C).
Direct Current Conventions

Direct current in electrical devices involves
the movement of charges in only one direction.
Definition of the current flow is a science
subject specific:
 Chemistry defines electricity as the flowing of
electrons (-) with their negative charges.
 Physics & Engineering define electricity as the
flowing of (+) charges of potential energy.
Ohm’s Law

The empirical relationship that states
the current is proportional to the applied
voltage divided by the resistance :
I = V/R or V = IR
 R is the resistance to electrical flow
measured in Ohms, , and is equal to
volts/amps.
 V is volts; which is electrical potential
energy in Joules/Coulomb.
Electrical Energy and Power

Since the change corresponding to a change
in potential, DPE= q DV, then the rate at
which energy as charge, Q, passes through a
resistor is DPE/ D t= (D Q/ D t) DV = IV.
 Therefore , power loss in a circuit is
P = IV = I2R = V2/R = W/t
Work done by Electricity

Work can be done by electricity with
electric motors or used by heating machines
like stoves and heaters.
 The cost of electric power is pennies per
kilowatt-hour (kWh) = 1000 watts used
continuously for one hour.
 1 kWh= (1000 W)(3600 s) = 3.6x106 J
Potential Energy & Electricity Fields

As an electric charge moves up or down an
electrical field it changes potential energy.
 PE electric = - qEd ; where PE is in Joules, q
is the charge in coulombs, E is the electric
field strength in Newtons/Coulomb, and
distance =meters.
/charge
+
Potential
energy
=Voltage
Electric Field
Strength
Potential Energy & 2 Charges

Charges interact with each other and
produce a non-uniform electric field. This
requires a different formula than a force.
 PE electric charges = k q1q2/ r
( note the
radius in NOT squared here – calculus
integration between force and PE.)
Parts of an Electric Circuit

Electric Circuit – a complete closed path
through which charges can flow.

There are 3 Basic Parts to an Electric
Circuit
1. Energy Source
2. Wires
3. Loads
Parts of an Electric Circuit
Parts of an Electric Circuit

Sometimes circuits will also contain a
switch. A switch is used to open and close
a circuit.
 When the switch is “on” the circuit is closed
and charges are able to flow.
 When the switch is “off” the circuit is open
and charges are NOT able to flow.
Parts of an Electric Circuit
Symbol Conventions for
Circuits.

Schematic
map keys for
electronic
components.
House Schematic Diagram
Direct Current Circuits
When a continuous conducting path (wire) is
connected between the terminals of a battery, it is
called a circuit. A map of its paths and components is
called Schematics
 Direct Current Circuits are those electronic pathways
that have only one direction of electrical flow and are
composed of :
 Power sources, conductive connectors, resistors,
switches, fuses, GFI’s and possibly capacitors.
 Monitoring of the circuits energy conditions is done
with ammeters, voltmeters and multipurpose-meters.

Series Circuits

Series Circuit – a circuit where all parts are
connected in a single loop.

All the loads in a series circuit must share
the same current. An example of this is that
if lights are wired in a series circuit they
will all glow the same. If another bulb is
added the bulbs will glow dimmer.
Series Circuits
Uses for Series Circuits

Series Circuits are useful in wiring burglar
alarms. If any part of the circuit fails there
will be no current in the system and the
alarm will sound.

Series circuits are not very useful in homes
since all the parts of the circuit must be
turned on for any part to work.
Resistors in Series Circuits
Resistors in Series
In a series circuit the sum of the voltage drops
equal the voltage drop across the entire circuit.

V = V1 + V2 + V3 etc....  Vi and also
V = IR1 + IR2 + IR3 …. The current
stays the same throughout the circuit.

The effective resistance in a series
circuit is the sum of all the resistors.

R = R1 + R2 + R3 etc....  Ri

The current through a series circuit is
found by calculating the effective resistance and
then using Ohms law in the form of I = V/R

Parallel Circuits

A parallel circuit is a circuit in which the loads are
attached side by side.

There is more than one path for charges to flow
within the circuit. We call the parallel paths
BRANCHES.

Loads connected in parallel can take advantage of
a power source’s full voltage. This allows all the
bulbs connected in parallel to glow at full
brightness. Also, if one of the bulbs goes out the
rest will keep working.
Parallel Circuits
Resistors in Parallel Circuits
Uses of Parallel Circuits

Useful in homes because you can turn off
one appliance on a circuit and are still able
to use the other appliances on that same
circuit.
Resistors in Parallel Circuits








In a PARALLEL circuit each resistor provides a new path for
electrons to flow. Each resistor can be operated independently
and if one path is open it will not affect any other parallel
pathway.
The total current in a parallel circuit is the sum of the currents
in its branches. The voltage remains the same throughout the
circuit.
I = I1 + I2 + I3 OR
I= V = V + V + V
R
R1
R2
R3 If you divide each side of
the equation by V::::
∑Rparallel = 1 =
1 + 1 +
1
R eq
R1
R2
R3
Take the inverse of 1/Req to find the equivalent resistance.
First: Add the Inverses of the
Resistors Values
Parallel Circuit Resistor
Addition
Adding parallel resistors
requires that you add the
inverses of the individual
resistors and then invert
the final sum.
Ex: look at the top
circuit:
1/6 + 1/6 + 1/6 = 0.5
Then take the inverse of
the sum: 1/0.5 = 2 Ώ
Effective Resistance
Summation in a Circuit
In analyzing a combination of series and
parallel circuits, you must first combine
parallel resistors into a single resistor.
 Then combine series resistors to find the
Total Effective Resistance of the Circuit.
 Ohm's law can then be used on each
separate part of a series - parallel circuit.

Total
Effective
Resistance
in a Circuit

Add parallels with
inverse summation.
 Then add series with
normal addition.
 = Total
Resistance
Circuit Resistor Summation
Water Flow Circuit Pattern:
Compare this to the electricity
Volume in = Volume out through the path of least resistance.
Parallel Circuit Current Flow
Patterns
Parallel Circuit Current
Addition
Batteries convert
chemical energy into
electrical energy!
douglasbattery.com
1. Dry Cell Battery
creative-science.org
2. Wet Cell Battery
channel4.com
Batteries
The parts of the battery ( electric cell) are the
electrodes (anode and cathode), a connecting
part (ion/salt bridge) for the electrodes and
the electrolyte.
 The simplest battery is just two different types
of metal divided by an electrolyte. Technically,
a series of electric cells makes up a battery.
For Example, a series of six 2 volt cells makes
up a 12 volt car battery.

Battery Mechanism

When the anode (usually zinc or other
electrically active metal) dissolves in the acidic
electrolyte and the cation goes out and leaves the
electrons (oxidation). Those electrons flow to the
cathode through the connecting bridge to the
cathode (reduction site) at a rate and potential
difference based upon how different the
electrochemistry is between them. This is the
Electro Motive Force (emf) in the battery.
AC/DC
Direct current (DC) is charge moving in one direction
•Alternating current (AC) is charge moving back and
forth.
•Batteries produce direct current (DC).
•The power company uses electrical generators to
produce alternating current (AC).
•120V of AC is available at your house’s wall
sockets.
•It is more efficient for power companies to send AC
to your house, but most electrical devices need DC.
•These devices have components called capacitors
inside them that convert AC into DC.
120V AC
9V DC
1.5V DC
Electrical Resistance.
– This is when current flow is slowed down.
– Current seems to lose energy. Actually, the electrical
energy is converted into heat and/or light.
– The symbol is R.
– The unit is the ohm ().
Water Heater Element
Stove Top Burners
Light bulb
Resistivity and Temperature
The resistivity  in most metals increases
linearly with increasing temperature.
 The hotter the wire / electronic; the more
the resistance.

A conductor’s electrical resistance depends on
Four Variables.
 The length of the conductor.
 The cross-sectional area of the conductor.
 The material of which the conductor is made.
 The temperature of the conductor.
Problem Types



1. Ohms Law with voltage, current,
resistance.
2. Power calculations
3. Circuit analysis
–
Simple series or parallel circuits
– Complex circuits with multiple branches
4. Capacitance
5. Daily Household electrical costs.
6. Transformer calculations
Complex Circuit Analysis

When a circuit has both parallel and series
circuits, the analysis of the total resistance
is done by
– adding all possible series resistors
– Then convert parallels to series
– Then finish adding all resistors in series.
Complex Circuit Analysis

Try this circuit:
Your Turn to Find Total Resistance
The relationship between voltage, current, and
resistance is
V = I · R or Ohm’s Law
fm-transmitter.com
V = Voltage
I = Current
R = Resistance
(SIM1) (SIM2)
esitest.com/img
Digital Multimeters
can measure voltage,
current, resistance,
and more.
Electrical Work.


A voltage source does work when releasing charge.
The unit of electrical work is joules (J).
Electrical Power.


The unit of power is called the watt (W).
power = current · voltage
P=I ·V
Paying for Electricity.




The electric company charges you based on the amount of
power and the amount of time.
Energy (electrical) = Power x Time
The unit is kilowatt-hour (kW-hr).
1 kW = 1,000 Watts
Transformer Equation

Vs = Ns = I p
Vp Np Is
Where V is voltage of
secondary / primary =
the number of wire
wraps N of the
secondary / primary.
Voltmeters and Ammeters

An Ammeter is used to measure current in a
circuit. It is hooked in series within the circuit to
measure the entire amount of electricity being
transmitted. It should have a very small
restriction effect upon the circuit.
 A Voltmeter is used to measure the voltage
potential within a circuit. It is hooked in parallel
and has a high resistance to measure the
electrical “pressure” pushing the current.
Voltmeters and Ammeters
Multi Meter

This meter has multiple
uses including as a
voltmeter
and an ammeter
Parallel Plate Capacitor

For a parallel plate
capacitor the voltage V is
given by the equation:
V= Ed;
 A capacitor can change
AC to DC inside of an
electrical device and
adjust radio freq.
Capacitance

A capacitor is a device that stores energy
temporarily. It is used to change AC to DC
current and tuning frequencies on radios
(and several other electric functions.) The
SI unit for capacitance is the Farad (F).
 C = Q / ΔV where Q is coulomb and V is
volts and
 C = ε0 A/d ; where ε0 is permittivity of free
space vacuum; A is area in m2 and d is
distance between plates in meters.
Dielectric = Insulation
between Capacitor Plates
Capacitors in a Circuit

Capacitors are shown by 2 equal size
parallel lines in schematics.
Potential Energy in a Capacitor

A charged capacitor stores electrical PE because
it requires work to move charges through a
circuit to the opposite plates of a capacitor.
 PE electric capacitor = ½ QV = ½ CV2 = Q2/2C
Capacitors
eere.energy.gov
Several
things in
our homes
consume
electricity.
eere.energy.gov
The hot
water
heater uses
electricity to
heat water.
Look for this
sticker to find
out how your
appliance
compares to
others that are
similar.
eere.energy.gov
This meter can usually be found outside our
home. It keeps track of the amount of electrical
power that your home uses over time.
It is illegal
to tamper
with it!!!
Where does electricity come from?
Power plants use
generators to
produce power.
This generator is
called a turbine.
Electric Generator
Electricity
is not
entirely
efficient.
Household Circuits

In the home, your circuits are wired in parallel to
allow for all electric appliances and motors to
have the same voltage.
 Circuit breakers, fuses and Ground Fault
Interrupters (GFI’s next to water sources) are
used in household circuitry to prevent shocking
and overheating of the electric circuitry.
 Common voltages are 120V and 240 V. Normal
appliances use 120V while larger ones require
240V ( electric stoves and clothes dryers).
Household Circuit Safety

Circuit Failure - Broken wires or water
can cause a short circuit. In a short
circuit, charges do not go through one or
more loads in the circuit. This can cause
heat to build up and fires to start.
 Fuses - A fuse has a thin strip of metal.
Fuses keep charges from flowing if the
current is too high. If the current does
get too high the strip of metal will melt
and the circuit will be broken.
Household Circuit Safety
 Circuit
Breakers - a switch that
automatically opens if the current is
too high. Charges stop flowing.
 Electrical Safety Tips - Do not
overload circuits by plugging in too
many electrical devices. Do not use
electrical devices near water.
Electrical Safety
Safety should always be foremost in everyone’s
mind. A small electrical shock produces
“tingling” and a large one can burn skin, stop
the heart, brain or both. We use electricity to
restart hearts in a direct shocking procedure
called “defibrillation”
 The first line of defense against electrical shock
is the insulation on the wires.
 Fuses, Circuit breakers and GFI’s are used to
prevent shocking. A circuit breaker is a
resetable / reusable fuse.

Electrical Fuses and
Circuit Breakers