Ohm's Law is one of the most important things that you will use throughout your electrical career. It is a mathematical tool which is of the greatest use in determining an unknown factor of voltage, current or resistance in an electrical circuit in which the other two factors are unknown.
In case you missed the first post on electric circuit theory, kindly read here Electric circuit theory 1 tutorial
Assuming you don't have an ammeter or it has burnt while you want to measure the current in a circuit and where you can buy the device is very far. But you only have a Voltmeter, Do you know that you can still measure the current in the circuit?
Don't worry, I will explain how you will do that.
There was once a German Physicist called Georg Simon Ohm (1787-1854), he discovered ohm's law which is the relationship between Voltage, Current and Resistance in any DC electrical circuit.
The law is stated below,
Ohm's law state that current is directly proportional to the potential difference across its ends, but temperature and others physical conditions of a conductor are kept constant.
What are the things that kept constant?
These are the things that kept constant listed below;
Now, from the law, we can derive this mathematical expression.
V ∝ I
From knowledge of basic mathematics, proportional(∝ ) symbol can be replaced by =K, where K is constant. But here what kept constant is Resistance R which implies that we will replace ∝ with =R.
Hence, V=IR. -------------- 1.0
Where,
V= Voltage, measured in volt(V)
I= Current,measured in Ampere(A)
R= Resistance, measured in Ohms(Ω)
Do you understand what we just did?
If you don't, kindly reread from the beginning of the tutorial.
Now, let's continue
From equation 1.0, do you know we can derive an expression for Current and Resistance? Yes, we can, by just using changing of formula.
Expression for Current(I)
By making I the subject of formula in equation 1.
Just dividing both sides by R, then we have
I= V/R ......................... 1.1
Is it clear?
I believed it is clear, can derive an expression for Resistance R?
So by following the same procedure as we do while deriving an expression for current I, then we can say,
R=V/I ............................1.2
Now, let me explain how to measure current in the absence of ammeter, you will measure the voltage using the voltmeter you have, resistance value can be determined using coding method(I will write on how to use coding method in my next post), we can then use equation 1.1 to determine the current.
This is all about Ohm's law, some worked example and how to use coding method to know the value of a resistor will be posted on my next post. I'll only be writing once in a blue moon now because of Exam.
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