CLASS: FORM THREE
TOPIC: SUMMARY NOTES ON RESISTANCE
SUMMARY NOTES ON RESISTANCE
Resistance
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Resistance is a measure of the opposition to current flow in an electrical circuit. It
measures how easy or difficult it is for electrons to move though a material.
Therefore, resistors are used in circuits to control the current.
The greater the resistance in a circuit, the smaller the current in the circuit.
The unit of resistance is the ohm, represented by the Greek symbol omega Ω.
The resistance of most conductors such as copper are low, making them good
conductors of electricity.
Unlike insulators like plastics which have high resistance.
Resistors
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A resistor is an electrical component that is used for either limiting or
regulating the flow of electric current in electrical circuits.
There are two types of resistors namely:
o Fixed resistor: A type of resistor with a resistance that is fixed and cannot
be changed. The circuit symbol for a fixed resistor is given below.
o Variable resistor: A component that is used to change and adjust the
resistance in a circuit. The circuit symbol of a resistor is given below.
Ohm’s law
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The Ohm’s law states that the current in a circuit is directly proportional to the
voltage across and inversely proportional to the resistance.
This is given as;
V=I×R
Where V= Voltage
I= Current
R= Resistance
Worked Example
The diagrams in this question show parts of circuits.
This circuit contains a 6 resistor. The current through the resistor is 2 A.
Calculate the voltage across this resistor. Show your working and give the unit with your
answer
Solution
From Ohm’s law, Voltage (V)= Current (I) x Resistance (R)
V= 2 x 6
V= 12 V
NB: Check your learners’ book for reference and sample questions to solve.