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Basic electricity principles
WP3
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Energy principles
A balloon moves forward as air
blows out at the back end.
An example of transformationof pressure into movement.
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Hot air ballon
Here heat from combustionis transferred into mechanical
energy, lifting the balloon into
the sky.
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Electrical charge
Comb
Hair
By combing electrons move from the hair to the comb.
The hair then is erected as their will be a lot of positive charges
Left on the surface of the hair. These charges are repelling each other
Causing the hair to erect.
+
+
+
+
---
-- +
++
-
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Electrical current
----
- --
--
-
--
-
---
Few electrons, low
current flow
--
--
--
Many electrons, high
current flow1 Ampere is approximately
67 000 000 000 000 electrons
per second
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Resistans
-
-
--
When electrons collide heat is generated
and the electrons dont flow so fast.
The current is reduced due to resistance.
There is low resistance in metallic materials like copper, while
high resistance in materials like stone or glass. Copper can be used
As a conductor while glass can be used as an electrically insulating
Material.
Heat
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Conductor area
-
-
--
Heat
-
There will be less electrical flow in a thinconductor than in a wide conductor
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Battery
+
-
-
There is a surplus of electrons causing them to flow from
the negative pole to the positive just like water flow from theupper vessel to the lower
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Potential energy transformed into
mechanical energy
The rotor rotates as the water
turns it around. This is the
Principles of hydro power.
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Electricity production from hydro
power
The rotor can drive a
generator, and then
electrical power
is produced
Generator
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Hydro power
The electrical power produced is proportional to the water heightAnd the water flow through the turbine.
Turbine
Generator
Water height
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Closed loop with a load
To get electrons to flow you need a closed loop in an
electrical conductor. If we want to turn the electron flow into
something useful there must also be a load in the circuit. This
can be a lamp, that is a resistor producing light, and not only
heat, when current is flowing through.
ResistorLamp
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Similarity between a resistor and a
valve in a pipe
ResistorValve
Pump
You can compare Voltage, Current and resistance with Pressure,
water flow in the pipe and pressure drop in a valve.
If the resistance is half, the current will be twice as high:
Voltage = Current * Resistance or U = I * R
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Energy versus power
20oC 25oC
Now Two hours later
30oC20oC
Small
radiator
Large
radiator
With the large radiator you have higher power, that is
gives more Energy per time period (like per hour)
Power = 0.5 kW
Power = 1.0 kW
Energy = 0.5 kW * 2 hours = 1 kWh
Energy = 1.0 kW * 2 hours = 2 kWh
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Energy versus power
20oC 25oC
Now One respectivelyTwo hours later
25oC20oC
Small
radiator
Large
radiator
With the large radiator we heat the room to 25 o C in one
hour compared to two hours with the smaller radiator
Power = 0.5 kW
Power = 1.0 kW
Energy = 0.5 kW * 2 hours = 1 kWh
Energy = 1.0 kW * 1 hours = 1 kWh
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Power generation
In a battery we produce directed current, DC.
In a generator we produce Alternating current,AC.
An example of a simple generator is the Dynamowhich produces the light for your bike.
To produce electric power with a generator weneed to produce a magnetic field.
A magnetic body always have a North and a Southpole, and a magnetic field between these.
An example is Earth.
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Magnetic field
N
S
N
S
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A magnetic field can induce an
electric current
when a conductor is moving through the field. This is calledinduction. The direction of the current is switching with
the direction of the conductor movement.
N S
e-
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Current in opposite direction when
conductor moves opposite direction
N S
e-
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Explanation
The electrical field in the conductor tries to
stop the movement of the conductor in the
magnetic field. When current passes the conductor, a
magnetic field is produced around it
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Current - field interactions
Field counteract
Fields enhance each other
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A coil becomes a magnet
Current is flowing through
the conductor
A magnetic field is produced turning the
coil into a magnet
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The field is enhanced by putting
a metal bar in the coil
N S
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A simple generator
.
Current in
through paper
Current out
through paper
A coil
S
N
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One period- the sinus curve
.
.
.A B
A
B
Max
..B A.
B
A
Max but
other
direction
..A B
One period
Current
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A motor is a generator but the
oppositeIn the generator the coil ( the rotor) is turned in the magnetic
field by a mechanical force and a current is generated.
In the motor a current is generating an alternating magnetic
field which is turning the coil, or the rotor as it is called.
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The transformer
When you move a conductor in a magnetic field an electricfield is created in the conductor. This is called EMF,
Electro Motoric Force.
The size of this depend on:
- The length of the conductor in the magnetic field
- How fast the conductor is moving in the field- How strong the magnetic field is
The first factor, the length of the conductor, is used in the
Transformer. High Voltages can be transformed to lowVoltages or the opposite.
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Transformer
Principally the transformer is two coils formed around
an iron frame, with different number of windings.
U2=Voltage =50V
N2=Windings =50 turnsU1=Voltage =100VN1=Windings =100 turns
N1 is twice as long as N2, and thus the voltage is twice as high.
The transformer is only possible to use for AC.
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Transformer
If the current is increased, the magnetic
flow is also increasing.
When the current flows in oppositedirection also the magnetic flow changes
direction.
The power is the same in both windings.
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Transformer power same at both
windings
U2=Voltage =50V
N2=Windings =50 turns
I2=current= 1 A
P2= power = U2*I2=50
U1=Voltage =100VN1=Windings =100 turns
I1=current= 0.5 A
P1=power= U1*I1= 50W
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Circuits in series
U = 20 V = 5+5+5+5 V
I = same in all lamps
U=5V U=5V U=5V U=5V
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Circuits in series
The serial circuits are comparable to if we have a water
pipe with several valves in series. If you first close one
vale a little, the flow goes down. If you then close the
second valve in series, the flow goes down even more. We
have the same with the resistances in the lamps
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Parallel circuits
It is more common to connect equipments and apparatus in
parallel. Then the current will vary in parallel lines.
Even here we can compare with water in pipes, but here
we have connected two pipes from one pump, in parallel.
If we then close one valve, the flow goes down in this line,
but it goes up in the other one! You can test it yourself
easily.
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Parallel circuits
20V
I= 2A
I1=0.5A
I1=0.5A
I1=0.5A
I1=0.5A
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The FuseThe purpose of the fuse is to protect expensive equipment
from to high currants.
TV Stereo PCFuse 10A
I=2A I=4A I=5A
Max current would be 2+4+5= 11 A if all apparatus are
in operation simultaneous. Then the fuse will break the
circuit. Otherwise there might be a fire instead, as the
conductors only are designed for 10 A.
If there is a short cut in some apparatus, the fuse will also
break the current, to save the rest and avoid fire.
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Measurements
A
Current is measured in
series
V R
Voltage and resistance are measured
in parallel
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Experiment for transformation of
mechanical energy into heat
Bend a spike up and down and sense the temperature change
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Heat to electricity
MagnetsWinding
Metal strip takingcurrent from the winding
that is turning around
When the candles are burning the heat turns the wheel around.
Then the winding is moving around in the magnetic field
between the magnets, and electricity is generated.
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Wind to electricityMagnetsWinding
Metal strip taking
current from the winding
that is turning around
The blow turns the wheel around.
Then the winding is moving around in the magnetic field
between the magnets, and electricity is generated.
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