This document discusses electrical resistance. It defines resistance as the opposition to the flow of electrical current and explains that all devices have some resistance. It introduces the resistance equation of Resistance=Voltage/Current (R=V/I) and describes how to calculate voltage, current, or resistance when two values are known. It also describes different types of resistors like fixed resistors, variable resistors, and special resistors such as diodes, thermistors, and light dependent resistors (LDRs), explaining how their resistance changes with factors like temperature, light intensity, or direction of current. It concludes by mentioning Ohm's Law, which states that current is directly proportional to voltage when resistance and temperature remain constant.

1. Chapter 10:
Electrical Resistance

2. Introduction
Today you will learn what resistance
is, and how it can be useful in
electrical appliances, some factors
affecting resistance and how to work
out the resistance of a component by
measuring the current and voltage
across it.you will also get to know
some special resistors, and their
uses

3. Resistance
Resistance is the opposition that an electrical device
has to the flow of electrical current.
All devices have some resistance.
A resistor is a device that has a particular resistance.

4. Resistance Equation
Resistance=Voltage/Current
R=V/I
• Resistance is measured in ohms
• Voltage in volts(V),Current in
amps(I)
• You can rearrange the equation to
find voltage & current
R=V/I
V=R*I
I=V/R

5. Text
Types Of Resistors
Fixed Resistors, Variable Resistors & Special
Resistors

7. Text
Fixed Resistors
These resistors have a fixed resistance in order to control the size of
currents and voltages.Resistors are included in circuits so that the
correct voltage is applied across the bulb and the correct current flows
through it.

8. Text
Variable Resistors
These resistors have different resistance and it's possible to
alter their resistance.when you alter the volume of television or
speed of a fan you use a variable resistor to do so

9. Text
Special Resistors
Diodes, Thermistor, LDR

10. Diodes
Diodes are resistors that
direct the flow of current
in one direction.
Used in rectifier circuit
to convert AC to DC.

11. Thermistors
A resistor whose resistance
changes with the temperature
Resistance of a thermistor⬇️
as the temperature⬆️
Eg:Temperature sensors in
fire alarms
High Temperature
Low Temperature
I
V

12. Light Dependent Resistors
(LDR)
A resistor whose
resistance depends on
light intensity
Resistance of a LDR⬇️ as light
intensity⬆️
Eg:Photographic equipment,
automatic lighting control, some
garage, gates
I
V
Bright light
Low light

13. Ohm's Law
The current that flows
through a conductor is
directly proportional to
the potential difference
across its ends,provided
its temperature remains
constant.
Obey's Ohm's Law
Doesn't Obey Ohm's Law

14. Text
Measuring resistance