Basic Electricity Energy & Environment This PowerPoint is created and developed by :
Dec 24, 2014
Basic ElectricityEnergy & Environment
This PowerPoint is created and developed by :
Basic Electricty
This assumes that all electrical and electronic effects are due to the movements of electrons
from one place to another
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The entire study of electricity is based on the Electron Theory
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Before we work with electricity we must know what an electron is and what causes it to move - ?
Lets look first at where we find electrons…in atoms
An AtomThe atom is the building block of all stuff, or what scientists call "matter".
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What things are made of atoms?
Electrons have a negative charge.Protons have a positive charge.Neutrons are neutral and therefore have no charge.
Electrically Neutral Atom
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-The number of protons=the
number of electrons
In an Electrically Neutral Atom:
So how many electrons will there
be?
It is the movement of these electrons
between different atoms that creates
electricity
CurrentThe flow of electrons is called the
current
Lots of electrons
–ve
Attracted to +ve
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The units of current is amps
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Conventional Current
The only way it can work is that the real negatives flowing in one direction are replaced with imaginary positives flowing in the other.
Historic physicists did not know about atoms and electrons when they created the rules for electricity.
They knew it was charge that moved but they didn’t know if it was +ve or –ve. They assumed +ve and
that’s what the rest of electrical rules have been based on
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-ve
+ve
-ve
G
-ve
+ve+ve
=Electron Flow
This is the way we will continue to think of current from now one
Conventional Current
Electromotive ForceFor electricity to flow, there has to be something to push the electrons along.
EMF is measured in volts
This is called an electromotive force (EMF)
A battery or power outlet creates this Electromotive force which induces current in a circuit.
EMF
Potential DifferenceThe difference in EMF across
two points is called the potential difference. (change in electrical potential energy)
What is the potential difference of this light bulb?
5 volts3volts5 volts-3 volts=2 volts
So where have the 2 volts gone?
+-They have been transferred from electrical energy into light energy.
ResisitanceNot all materials give up their
electrons easily.
Remember that metals give up electrons easily whereas non
metals do not give away electrons readily
This reluctance to give away electrons is called resistance.
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High Resistance
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Low Resistance
Non metal-high
resistance
Metal-low resistanc
e
Resistance Example
Do these materials have high or low
resistance?
lowlow
high
high
high
PowerPower=work done
Work done= moving an electron from one place to another
Power is measured in Watts
Power =EMF x CurrentWatts= Volts x Amps
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-EMF
Current
Power =
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A B
Power Exercise 1Power =EMF x CurrentWatts= Volts x Amps
What is the power of CFL bulb ?
(CFL stands for compact filament lamp)
What is the power of filament bulb?
EMF=2 voltsCurrent=11 amps
EMF=8 voltsCurrent=11 amps
Which is better to use and why?
Electrical Energy
Work done in a period of time
Units=Kilowatt Hours (kwh)
Kilowatt Hours (kwh)= power x time = EMF x current x time
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Electrical Energy Example 1
Length of time on a day=2 times x 20 minutes=40 minutes /day
Convert to hours=40 mins 60 mins/hour=0.66 hour
Electrical Energy = 800 watts x 0.66 hour =52.80 watt hours =0.0528 kilowatt hours
A hand grinder in the Vigyan Ashram workshop has a power rating of 800 watts. It runs for 20 minutes a session and is used 2 times a day. Calculate the daily electrical energy that is needed in kwh.
Electrical Energy Example 2The water pump at Vigyan Ashram uses 4.4kwh a day. It is on for two hours a day. If the EMF of the pump is 230 volts what is the current used?
Electrical energy used in one hour=4.4kwh a day 2 hours a day= 2.2 kw=2200 watts
Electrical Energy= EMF x current x time
Current= Electrical Energy EMF = 2200 230 =9.56 amps
1. What direction does conventional current go?
2. What is resistance? Name a material that has high resistance and low resistance.
3. What is EMF and what is its units.4. How can you find the power of an
appliance if you know the EMF and current?
5. How is electrical energy different from power?
Summary Questions
+ve -ve
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