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Electron and Electricity
Electricity is the movement
of electron thought a
material.
Electron flows along like a
water current in a stream,
so we call it Electric current.
You need something to give
energy to electrons. You
need a battery and the
power of it is called voltage.
The higher the voltage, the
more power there is to drive
the electrons thought the
circuit
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Electron and Electricity
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Voltage is like the
Steepness of a river.
The bigger the different
in height between the
start and the end of the
river, the faster the
water current will flow.
Voltage is measured in
Volts
Electrical Resistance
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Materials such as copper or aluminium
metals that conduct electricity are called
conductors. Materials that don't allow
electrons to pass through them, such as
rubber and plastic, are called insulators.
Resistance is a measure of How an object
opposes the passage of electrons. The unit of
electrical resistance is the ohm.
Electrical Resistance
Every materials has Resistance. Copper has a low resistance
and the wood has a high resistance.
For example, a meter of copper has only 1 Ohm but a meter
of wood has 10000000 ohm
We need resistance to reduce the flow of electrons thought a
circuit, so we can build resistor to behave as Electrical
resistance.
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Reading Resistor Values
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The resistance of resistors is indicated using colour-coded
bands on the body of the resistor
The first three coloured indicates the value of the resistor in
Ohms. The first band tells us the first digit, the second band
tell us the second digit and the third band tell us the number
of zeros
Color Code Table
Examples
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A) If the first band is green (5) the second
digit is blue (6) and the third band is orange
(3), the value of the resistor is 56000 ohm.
Because 1000 Ohm = 1 K, we have 56k
B) red, red, yellow. So we have 2, 2, 0000 or
220.000 Ohm
Exercises
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1. What resistor values are indicated by the
following colour bands?
(A) red, black, red
(B) grey, red, orange
(C) orange, white, blue
(D) green, white, black
2. What are the colour codes for the following
resistance values?
(A) 2.2k (B) 270 (C) 56 k
3. What are the maximum and minimum values of a
resistor with the following colours:
Red, orange, brown with a gold tolerance band
Ohm´s Law
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There is a relationship between Voltage,
Current and resistance.
The current in a circuit ( amp) is directly
proportional to the applied potential
difference (volts) and inversely
proportional to the resistance of the
circuit ( resistance).

I = v/r
Ohm´s Law

A nine volt battery
supplies power to bulb
with a resistance of 18
ohms. How much
current is flowing
through the bulb?
Solution: Substitute in
the values for
V(Voltage) and
R(Resistance).
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I = v/r
Problem 1
A 110 volt wall outlet
supplies power to a Tv
set with a resistance of
2200 ohms. How much
current is flowing
through the Tv?
Problem 2
A CD player with a resistance of 40 ohms has a
current of 0.1 amps flowing through it.
Calculate how many volts supply the CD
player?
Choose your answer below
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10.0 volts
0.0025 volts
400.0 volts
4.0 volts
Designing a resistor network
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Sometimes you need a kind of resistor, but you don't have it
on hand and it doesn't exist. Fortunately, it's possible to use
several different resistors in combination to get virtually any
level of resistance, for example if you have 2 resistor of 20
Ohm and you need a resistor of 40 Ohm, just add both in
serial , so Rt = R1 + R2 + ……… ( Serial )
Designing a resistor network
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In the Figure you can see three resistors, but this
time they're connected in parallel. Each electron will
flow through one of the three resistors.
This three resistor have a equivalent resistor of:
A Easier Serial Formula
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The formula
is a bit difficult
to remember, So could we find something
easier?
Yes, come on… try on
A Easier Serial Formula
1
1
1
R1
R2
R1 R2
1
R2
R1
R1
R1
1
R2
R1
R1 R2
R1
R2
R2
R2
Electron and Electricity
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In this circuit, calculate:
A) the total resistance
in the circuit?
(B) the total current
flowing at point A?
Electron and Electricity
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This is a circuit the
resistors are in parallel:
 Calculate:
A) the total resistance
in the circuit?
(B) the total current
flowing at point B and
the current at C and D?
Electron and Electricity
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In this circuit, calculate:
A) the total resistance
in the circuit?
(B) the total current
flowing at point A?