Georg Simon Ohm

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Ohm's Law ????
Georg Simon Ohm
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Georg Simon Ohm
Georg Simon Ohm, 1789-1854, German
physicist. Born 16 March 1789 in Erlangen,
Bavaria (now Germany) Died 6 July 1854
in Munich, Bavaria, Germany Ohm's most important
discovery (of 1826) now bears his name .Ohm's
importance was not recognized through most of his
lifetime, but in 1852 he became professor of
physics at the University of Munich.
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Ohm's Law
The unit of resistance is called Ohm in honor of
a German scientice by the name of Georg Simon
Ohm, who discovered that when a conductor has a
resistance of 1 ohm than an emf of 1 volt will
cause a current of 1 amp to flow through a
conductor. This is a very simple bit of
physics. Ohm's Law says that there is a
relationship between these three factors. So if
you know two of the values you can easily work
out the third one.
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Ohm's Law

• This equation is what Ohm's Law says.
• V I x R
• I V /R
• R V / I

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Ohm's Law
An easy way to remember the formulas is by using
this diagram. To determine a missing value,
cover it with your finger. The horizontal line
in the middle means to divide the two remaining
values. The "X" in the bottom section of the
circle means to multiply the remaining values.
If you are calculating voltage, cover it and
you have I X R left (V I times R). If you
are calculating amperage, cover it, and you have
V divided by R left (IV/R). If you are
calculating resistance, cover it, and you have V
divide by I left (RV/I). Note The letter E is
sometimes used instead of V for voltage.
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Example
In this simple circuit there is a current of 12
amps (12A) and a resistive load of 1 Ohm (1W).
Using the first formula from above we determine
the Voltage V 12 x 1 V 12 Volts (12V) If
we knew the battery was suppling 12 volt of
pressure (voltage), and there was a resistive
load of 1 Ohm placed in series, the current would
be I 12 / 1 I 12 Amps (12A)
If we knew the battery was suppling 12V and the
current being generated was 12A, then the
Resistance would be R 12/12 R 1W
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Voltage

• This is sometimes called potential difference or
  PD. It is measured in Volts. If you have not
  learnt about voltage before, you will certainly
  have seen something like 1.5v on the side of the
  batteries which you put in your walkman. The "V"
  in the formula given above stands for voltage.
  Here are some typical values
• 70mV the voltage across the inside and outside of
  a human nerve
• 1.5v the voltage of a walkman battery
• 6v the voltage of a moped battery
• 12v the voltage of a car or motorcycle battery
• 24v the voltage of a 50 seater coach battery
• 110v mains voltage in the USA some continental
  countries
• 240v nominal mains voltage in the UK
• Thousands of volts voltages in amateurs' antennas
  whilst transmitting
• Tens of thousands of volts voltages in overhead
  power cables

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Voltage
As you can see, there is a lot of difference
between the voltages in our nerves and muscles
and the voltages in the mains power supply. It
does not make a lot of sense to put your fingers
in the mains power sockets! So be careful not to
hang onto my long wire antenna when I am
transmitting. You can charge yourself up with a
van de Graaf generator to a few thousand volts,
but the currents involved are quite small, it is
not the same with the mains which could give you
a lethal shock. I have tried it once and it was
not a pleasant experience. 1.5 volts might be
enough to light up a small tent with a torch, but
not enough to light up your living room. 1mv
(one millivolt) is 1 thousandth of a volt. 1Mv
(one Megavolt) is 1 million volts.
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Voltage
Batteries, the mains, dynamos and electrical
generators provide the energy to force electrons
around electric circuits. The bigger the voltage
is the greater the "force" making electrons go
round a circuit. You can think of it as being
like a hill if you fall down the hill you could
roll to the bottom. The steeper the hill is the
quicker you will roll down it.
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Current
Current is measured in amperes or amps for short.
We use the symbol "I" in the formula to represent
current. (The reason for using "I" rather than
"C", is that "C" is already used for something
else.) The kinds of current flowing in our
nerves and muscles is only a few microamps the
currents flowing in the mains might be as much as
13 amps. The currents flowing in my antenna
could be very much higher! Please don't touch my
antenna whilst I am transmitting.
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Resistance
Resistance is to do with how easy it is for the
electric current to flow through a material, e.g.
a piece of copper wire. Although your physics
teacher will tell you that copper is a very good
conductor of electricity, it does have a
measurable resistance. Some materials have
virtually no resistance when they are cooled down
to absolute zero, they are called super
conductors. Mercury will do this. Materials
like plastic, wood, polythene, ceramics and
rubber have very high resistances so that it is
almost impossible for electric currents to flow
through them. These materials are called
insulators. They may not be perfect.
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Resistance
Materials like copper, silver, and gold have very
low resistances. In fact all metals will conduct
electricity. They are called conductors. Even
so, they do have some resistance to the flow of
electrons through them. A perfect conductor is
called a superconductor, it has zero resistance.
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Resistor
AH/AS Type
MH/MV Type
GF/MF Type
CH Type
QH Type
CD Type
CF/QF Type
CR/QR Type
CE Type
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Reference
http//www.purchon.co.uk/radio/ohmslaw.html http
//www.electronics-tutorials.com http//webhome.id
irect.com/jadams/electronics/ohm.htm http//www.
energy.ca.gov/education/scientists/ohm.html http
//www.english.upenn.edujlynch/Frank/People/ohm.ht
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