3 | Ohm's Law

The formula

This is the law stating that electric current is proportional to voltage and inversely proportional to resistance. 

Formula; 

        Voltage,  V = I x R           units is volts or 'V'

       Current,   I = V ÷ R         units is ampere or 'A'

        Resistance,  R = V ÷ I   units is omega or 'Ω'



Note:  If any incorrect calculated values will results in damaging the circuit (or load) may suffer burn or cable burn due to cable under size.

Figure 1  Ohm's Law formula.

Basic Circuits and Ohm's Law

Basic circuit and ohm's law work together, therefor basic circuit must be CLOSE circuit formation. If any of the circuit lines is broken or open then current will not flow and no load will operates.   

Refer to figure 2 is complete close loop of the circuit will the following electrical elements.  

Figure 2 Close circuit  

Example calculation 

1)   Given the current is 2.5 ampere and a resistors is 40 Ω, calculate the voltage, V?

         Answer:      Apply the formula     V = I x R     

                                   V  = 2.5 A x 40 Ω  = 100 v  (or volts)


2)   The voltage total is 230 volts and the current flow in the circuit is 3.25 A, find the resistance R? 

        Answer:      Apply the formula    R = V ÷ I     

                                R = 230 v ÷ 3.25A  =  70.76 Ω  (or ohm)


3)   A resistance is 530 Ω and supply voltage is 120 volts, find current I?

        Answer:      Apply the formula     I = V ÷ R     

                                   I = 120 v ÷530 Ω  =  0.22 A   (or ampere)