4. •Flow of electric current through a conductor experiences a certain
amount of resistance.
•The resistance, expressed in ohms (W, named after George ohm),
kilo-ohms (kW, 1000W), or mega-ohms (MW, 106W) is a measure of
how much a resistor resists the flow of electricity.
•The magnitude of resistance is dictated by electric properties of the
material and material geometry.
•This behavior of materials is often used to control/limit electric current
flow in circuits.
•Henceforth, the conductors that exhibit the property of resisting
current flow are called resistors.
Resistor Symbols
5. •A resistor is a dissipative element. It converts electrical energy into heat
energy. It is analogous to the viscous friction element of mechanical
system.
•When electrons enter at one end of a resistor, some of the electrons
collide with atoms within the resistor. These atoms start vibrating and
transfer their energy to neighboring air molecules. In this way, a resistor
dissipates electrical energy into heat energy.
•Resistors can be thought of as analogous to water carrying pipes. Water
is supplied to your home in large pipes, however, the pipes get smaller as
the water reaches the final user. The pipe size limits the water flow to what
you actually need.
•Electricity works in a similar manner, except that wires have so little
resistance that they would have to be very very thin to limit the flow of
electricity. Such thin wire would be hard to handle and break easily.
6.
7. Resistors are used for:
• Limiting current in electric circuits.
• Lowering voltage levels in electric circuits (using voltage
divider).
• As current provider.
• As a sensor (e.g., photoresistor detects light condition,
thermistor detects temperature condition, strain gauge
detects load condition, etc.)
• In electronic circuits, resistors are used as pull-up and pull-
down elements to avoid floating signal levels.
8. It is very important to be aware of power rating of resistor used in
circuits and to make sure that this limit is not violated. A higher
power rating resistor can dissipate more energy that a lower
power rating resistor.
Resistors can be made of:
• Carbon film (decomposition of carbon film on a ceramic core).
• Carbon composition (carbon powder and glue-like binder).
• Metal oxide (ceramic core coated with metal oxide).
• Precision metal film.
• High power wire wound.
10. A RESISTOR IS A PASSIVE TWO -
TERMINAL ELECTRICAL COMPONENT THAT
IMPLEMENTS ELECTRICAL RESISTANCE AS A CIRCUIT
ELEMENT.
THE RATIO OF THE VOLTAGE APPLIED ACROSS A
RESISTOR'S TERMINALS TO THE INTENSITY OF
CURRENT THROUGH THE CIRCUIT IS CALLED
RESISTANCE.
THIS RELATION IS REPRESENTED BY OHM'S LAW:
V = I R
11.
12.
13.
14. THE OHM (SYMBOL: Ω) IS THE SI UNIT
OF ELECTRICAL RESISTANCE, NAMED
AFTER GEORG SIMON OHM.
AN OHM IS EQUIVALENT TO A VOLT PER AMPERE
OTHER DERIVED UNITS ARE MILLI OHM (1 MΩ =
10−3 Ω), KILO OHM (1 KΩ = 103 Ω), AND MEGA OHM (1 MΩ
= 106 Ω).
FIXED RESISTOR
VARIABLE
RESISTOR
15. Calculate the current through a 3 Ω
resistor when a voltage of 12V is
applied across it.
Answer: ?
20. The resistive value of the
resistor is controlled by
increasing the desired thickness
of the deposited film.
Resistane upto 10mω can be
obtained.
Have tolerance 1% or less
21. Made by winding a thin metal
alloy wire onto an insulating
ceramic former in the form of a
spiral helix
Available in very low ohmic
and high precision values
(from 0.01 to 100kω)
22. Rheostat is a adjustable
resistor used in applications
that require adjustment of
current or varying of resistance
in an electric circuit
A special type of rheostat is
the potentiometer
23. A potentiometer is, a pot, in
electronics technology is a three-
terminal resistor with a sliding
contact that forms an
adjustable voltage divider.
Potentiometers are commonly
used to control electrical devices
such as volume controls, joysticks
etc.
24. A thermistor is a type
of resistor whose resistance varies
significantly with temperature
Thermistors can be used as
current-limiting devices for circuit
protection, as replacements for
fuses
25. A humistor is a type
of resistor whose resistance varies
significantly with humidity
A humidity sensor measures the
humidity level by measuring the
change in the resistance of an
element
26. A varistor (or voltage dependent resistor )
Function is to conduct significantly increased current
when voltage is excessive.
HIGH VOLTAGE
VARISTOR
27. A photoresistor or light
dependent resistor (ldr)
exhibits photoconductivity.
Photoresistors in many
consumer items such as street
lights, clock radios, alarm
devices etc
28.
29. IN SERIES CONNECTION, THE CURRENT REMAINS
CONSTANT.
(i.e. I = I1 = I2 = …. = In )
IN SERIES CONNECTION, VOLTAGE ADDS UP.
(i.e. V = V1 + V2 + …. + Vn)
30. PARALLEL CONNECTION
IN PARALLEL CONNECTION, THE VOLTAGE REMAINS
CONSTANT.
(i.e. V = V1 = V2 = …. = Vn)
IN PARALLEL CONNECTION, CURRENT ADDS UP.
(i.e. I = I1 + I2 + …. + In )
35. Wire-wound resistors have a label indicating resistance and power
ratings.
A majority of resistors have color bars to indicate their resistance
magnitude.
There are usually 4 to 6 bands of color on a resistor. As shown in the
figure below, the right most color bar indicates the resistor reliability,
however, some resistor use this bar to indicate the tolerance. The color
bar immediately left to the tolerance bar (C), indicates the multipliers (in
tens). To the left of the multiplier bar are the digits, starting from the last
digit to the first digit.
Resistor value = )%(10 W tolAB C
46. The first band is yellow, so the first digit is 4
The second band is violet, so the second digit
is 7
The third band is red, so the multiplier is
Resistor value is
)%(51047 2
W
2
10
47. Resistor colour code calculation
The first band red has a value of
2
The second band purple has a
value of 7
The third band has a multiplier
of x 10
The last band indicates a
tolerance value of +/-5%
Resistance value is 270Ω +/-5%
2
7
x10
+/-5%
