Nature of Electricity

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Nature of Electricity
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Nature of Current Electricity

• To make things work
• Need source
• 1.5 V cell has a limited life ( use it then throw
  it away)
• 240 Hydro Electric Cell virtually limitless

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Nature of Current Electricity

• To make things work
• Need Thing
• A device that converts energy into a different
  form of energy
• Heat, light, sound, motion, etc

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Nature of Current Electricity

• To make things work
• Need Switch
• Interrupts the circuit
• Wire
• Carries the electrons to and from the thing

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Why do we need two wires?

• the motion of electrons from high potential
  energy to low potential energy
• One wire carries electrons to the globe or CD
  player from the source, the other returns them to
  the source whereupon they are boosted back up to
  continue their circulation

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Law of Repulsion and Attraction

• Like charges repel and unlike charges attract.
• Negative electrons are pushed away from the
  negative terminal and are attracted to the
  positive terminal

In a battery how do charges flow?
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Measuring Current

• Current is represented by the symbol (I)
• Current is measured in Amps
• Current is measured using an Ammeter which
  measures the number of electrons passing through
  a circuit at a given point

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Current

• One amp is equal to the flow of one coulomb of
  charge per second.

COPYDIAGRAMS
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1. A current of 2 A flows for 30 seconds through a
   lamp.How much charge has moved?
2. A current of 12 A flows for 20 minutes into an
   electric cooker.How much charge has the cooker
   used?
3. If 18400 C of charge flows through an air
   conditioning unit every hour, what current does
   it draw?
4. A current of 3 A flows into a television set. For
   how long would it take 1500 C of charge to flow
   through it?

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What is VOLTAGE?

• In order for current to flow something has to
  make it flow
• Voltage
• Voltage measures the energy available to drive
  the flow of current.
• Provided by an energy source like a battery
• Measured in volts (by a voltmeter)

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Potential Difference

• The Voltage available to drive a flow of current
  is called Potential Difference

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There is a direct relationship between voltage
and current.We can demonstrate this with the
circuit below which connects a cell and a lamp.
The cell has an output of 2 volts.The lamp
glows moderately.
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If we replace the 2-volt cell with a 1-volt cell,
the lamp will glow dimly.This is because a
1-volt cell provides half as much energy as a
2-volt cell, so the lamp converts less energy
into heat and light.But how was the current
affected?
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To find out how the current was affected we
repeat the experiment, adding an ammeter. As
before, the cell has an output of 2 volts and the
lamp glows moderately.But this time we know that
the current is 1 amp.
As before, we replace the 2-volt cell with a
1-volt cell and the lamp glows dimly.But what
does the ammeter read?
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The ammeter reads 05 amps. The current is
halved because a 1-volt cell provides half as
much energy as a 2-volt cell.
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This time we connect a cell with an output of 4
volts.The ammeter reads 2 amps and the lamp
glows brilliantly.
Now we replace the 4-volt cell with a 2-volt cell
and the lamp glows moderately. The ammeter reads
1 amp. The current is halved because a 2-volt
cell provides half as much energy as a 4-volt
cell.
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• Voltage Current Summary
• Voltage is the energy that drives the flow of
  current.
• Voltage is measured in volts with a voltmeter
• Voltage is represented by the symbol, V.
• One volt is the energy required to drive a
  current of one amp through a circuit with a
  resistance of one ohm.
• An increase in voltage means an increase in
  energy and therefore an increase in current.
• A decrease in voltage means a decrease in energy
  and therefore a decrease in current.

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Resistance Resistors

• Resistance Resistors
• When walking, we don't normally notice we are
  moving through air as it offers such little
  resistance to our motion.
• But compare moving through air with moving
  through water which offers significant resistance
  to our motion.
• It's the same for a current moving through a
  conductor...

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Conductors

• All conductors offer resistance to the flow of
  current. This resistance is determined by the
  conductor's atoms.
• For example
• Silver and copper atoms offer negligible
  resistance to an electric current because a
  significant proportion of their electrons are
  free to move from atom to atom.Silver and
  copper, having negligible resistance, are
  commonly in used as conductors.
• On the other hand...

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Insulators

• Glass and Plastic offer very considerable
  resistance to an electric current because a
  significant proportion of their electrons are not
  free to move from atom to atom.Glass and
  synthetic polymers, having very considerable
  resistance, are commonly used as insulators.
• A conductor's length, temperature, and
  cross-sectional area also affects its resistance.

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Ohm's Law

• In Voltage Current we explained the
  relationship between voltage and current.
• In Resistance Resistors we explained the
  relationship between resistance and current.
• Here we explain the relationship between all
  three.

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• The relationship between voltage, resistance and
  current is expressed in Ohm's Law which is named
  after the physicist who discovered it.
• Ohm's Law most simply translates to the equation,
  V IR, or
• Voltage Current Resistance
• This is all, however, at a constant temperature

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• We can demonstrate the relationship between
  voltage, current and resistance in the circuit
  below which connects a cell, an ammeter and a
  resistor.
• The cell provides a voltage of 1 volt.The
  resistor has a value of 1 ohm.The ammeter reads
  a current of 1 amp.
• If we replace the 1 ohm resistor with a 2 ohm
  resistor, what will the ammeter read?

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• A 2 ohm resistor is twice as resistant as a 1 ohm
  resistor, so it is twice as hard for the current
  to flow. The resistor allows half of the 1 amp
  current to pass.
• By Ohm's Law
• V IR
• Solving for I
• Now replacing the symbols with the values given
• 0.5 I
• I 0.5 amps

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• Summary
• The relationship between voltage, resistance and
  current is expressed in Ohm's Law which most
  simply translates to
• V IRorVoltage Current Resistance
• Which is true only at a constant temperature.

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