Basic ElectricityEnergy & Environment

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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

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-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

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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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