Ohm’s Law

Before we get down with voltage divider and the rule, let us quickly checkout on Voltage, Current and Resistance. As these make up the ohm’s law.

Volt age
Voltage is how much energy is between two points on a circuit. These two points have different charges, one is higher and the other is lower. The difference between these
two points of the charge is how we measure the voltage.

In other words, voltage is the driving force in electrical circuit.

The unit of “volt” is the name of the Italian physicist Alessandro Volta who created the first chemical battery. The letter “V” represents voltage.

Current is how fast the charge is flowing. The higher the charge, the faster the current. Current has to do with electrons flowing in a circuit. Current measures how fast
the electrons go.

The unit of the current is “ampere,” and usually, a person writes it as “Amps”. The letter “I” can represent as current.


Resistance is how much the circuit resists the flow of the charge. This makes sure the charge does not flow too fast and damage the components. In a circuit, a light bulb can be a resistor. If electrons flow through the light bulb, then the light bulb will light up. If the resistance is high, then the lamp will be dimmer. The unit of resistance is “Ω”, which is called omega, and pronounced “ohm”, it is the name of the inventor of Ohm’s law.

You could visit busybrained.com/?p=40 for extensive analysis on resistor and its resistance.

Now, Ohm’s Law

Ohm’s law states that the electrical current (I) flowing in an circuit is proportional to the voltage (V) and inversely proportional to the resistance (R) so long as the temperature and other factors are kept constant.

Therefore, if the voltage is increased, the current will increase provided the resistance of the circuit does not change.

To make a current flow through a resistance there must be a voltage across that resistance. Ohm’s Law shows the relationship between the voltage (V), current (I) and resistance (R).
Ohm’s Law can be written three ways:

1. V = I*R

2. I = V/R and

3. R = V/I

V = voltage in volts (V)
I = current in amps (A)
R = resistance in ohms (Ω)

Ohm’s Law Calculations

Use this method to guide you through calculations:
. Write down the Values , converting units if necessary.
. Select the Equation you need
. Put the Numbers into the equation and calculate the answer.

It should be very Easy now! See the examples below:

Example 1:

3V is applied across a 6Ω resistor, what is the current?
Values: V = 3V, I = ?, R = 6Ω
Equation: I = V / R
N umbers: Current, I = 3 /6 = 0.5A

Example 2:

A lamp connected to a 6V battery passes a current of 60mA,
what is the lamp’s resistance?
Values: V = 6V, I = 60mA, R = ?
Equation: R = V /I
Numbers: Resistance, R = 6 / 60 = 0.1k = 100
(using mA for current means the calculation gives the
resistance in k )

Example 3:

A 1.2k resistor passes a current of 0.2A, what is the
voltage across it?
Values: V = ?, I = 0.2A, R = 1.2k = 1200Ω
(1.2k is converted to 1200Ω because A and k must not be used together)
Equation: V = I × R
Numbers: V = 0.2 × 1200 = 240V