Electricity. What is Electricity? Electricity is everywhere: Houses Cars Batteries Clouds.
Electricity
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Transcript of Electricity
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
ELECTRICITY REVISION
Basic elements in an electric circuit:Components that produce electric current (e.c.)Components that conduct an e.c.Components that transform an e.c.Components that control the flow of e.c.
Basic electric magnitudes:VoltageIntensityResistance
Ohm's Law
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
ELECTRICITY REVISION
Components that produce e.c.:Batteries and generators
Components that conduct an e.c.:Wires of conductor materials.
Components that transform an e.c.:Electric motor, light bulb, electric fire, resistors
Components that control the flow of e.c.:Switches, circuit switches, push button N.O. and N.C.
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
ELECTRICITY REVISION
Basic magnitudes :MAGNITUDE DEFINITION UNITS
RESISTANCEOpposition that materials offer to electric current flow.
OHMS (Ω)KΩ = 1000 Ω = 10 3 ΩMΩ = 1000000Ω = 106 Ω
INTENSITYNumber of charges that go through the section of a conductor per unit of time.
AMPS (A)mA = 0,001A = 10-3AμA= 0,000001A = 10-6A
VOLTAGEEnergy difference between both of the extremes of a conductor.
VOLTS (V)KV = 1000V = 103 VMV= 1000000V
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
ELECTRICITY REVISION RESISTORS
There are 2 types:
fixed resistors:
variable resistors:
fixed resistor Potentiometers
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
ELECTRICITY REVISION RESISTORS
Fixed resistors:
These resistors have a fixed value represented by a
colour code that we can observe over their surface.
The most common are those of coal, they are small
cylinders of graphite recovered with a film of paint
and they have two terminals to connect them.
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
VARIABLE RESISTORS POTENTIOMETERS
Its value can be changed with a cursor or turning an axle.The resistance varies from 0 ohms to a maximum value indicated at potentiometerApplications
Thermostat of a heatingVolume control of a radio
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
ELECTRICITY REVISION Ohm's law
Ohm's law relates the intensity that flows through a conductor whith its resistance and the applied voltage.
VI= ― R
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
SERIES CIRCUITS
They are circuits where components are connected
one behind the other.
There is a different tension in each component, but
through all circulates the same intensity.
Resolution:
R e = R
1 + R
2 + R
3 + … = ΣR
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
PARALLEL CIRCUITS
They are circuits where components are connected
with two common points.
Through each component circulates a different
intensity but all have the same voltage.
Resolution: 1 1 1 1 1 = + + = Σ R
e R
1 R
2 R
3 R
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
MIXED CIRCUITS
They are circuits that have components connected
either in series or in parallel.
Resolution:
There is not an only way to solve these circuits.
We have to calculate equivalent resistances by
sections.
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
POWER AND ENERGY
Power is the electric magnitude that measures the
consumed energy per unit of time.
We represent it by P and it is measured in watts
(W).
If in a component circulates an intensity I and it is
fed with a voltage V, then, the power that consumes
it is calculated like:
P = V · I
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
POWER AND ENERGY
Power is a characteristic of all electrical devices.All electrical appliances present the relation of their electrical characteristics. We refer to that like nameplate.
Voltage
Power
Frecuency
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
POWER AND ENERGY
Energy consumed by an electrical device is determined by its power and the time in which it is running:
E= P·tConsumed electrical energy it is measured in W·s or in KW·hIf an electrical appliance is has a voltage of 230 V and consumes 640 W, then we can calculate its resistance like: R=V2/PThen R = 2302/640 = 82,65 Ω
Dpto. Tecnoloxía, IES de Pastoriza, Arteixo
POWER AND ENERGY
The consume in the electric bill is measured in kWh (power in kW and time in hours)If we multiply by the price of a kWh, we obtain the cost of use of that electrical appliance.Example: The cost of use of a hairdryer of 2200 W running during 30 minutes is
P = 2200 W = 2,2 kW
t = 30 min = 0,5 h
E = P.t = 2,2 . 0,5 = 1,1 kWh (consumed energy)
If the price of a kWh is 0.12 €, then the cost is: 1,1 x 0,12 = 0,13 €