Ohm’s Law

We all know that electrons flow through the circuit because of the electromotive force or voltage. Great amount of voltage applied in the circuit will cause more electrons to move from one point to another, or the greater the intensity of the current flowing in the circuit. Connecting resistor with high amount of resistance in the circuit will decrease the intensity of current flow. This relationship between voltage, current and resistance is stated in Ohm’s law.

Ohm’s law is formulated by a German physicist named Georg Simon Ohm. According to Ohm’s law, the electric current flowing through the circuit is directly proportional to the voltage applied in the circuit and inversely proportional to the resistance offered by the circuit. Ohm’s law can be expressed as an equation:

E = IR

where:

• E is the voltage expressed in volts (V)
• I is the intensity of current flow expressed in ampere (A)
• R is the resistance expressed in ohms (Ω)

E=IR can also be written as:

I = E/R  and  R = E/1


THE MAGIC TRIANGLE

The Magic Triangle

The magic triangle can be used to obtain Ohm’s law formula. To get the voltage formula, just put your thumb over “E” on the triangle and you are left with “I” and “R”, which means that the E is the product of I and R (E = IR). For the current (I) formula, just put your thumb over the current symbol and you will have voltage over resistance (I = E/R ). To get the formula for resistance (R), just cover “R” and you are left with the formula voltage divided by current ( R = E/I ).

Example:

1. A circuit has an effective resistance of 1000Ω and the applied voltage of 50V. How much current is flowing through the circuit?
   
   GIVEN:
   R = 1000Ω
   E = 50V
   I = ?
   
   SOLUTION:
   I = E/R
   I = 50volts / 1000 ohms
   I = 0.05 ampere
   
   
   
2. In a circuit containing a 500Ω resistor, about 0.5A of current is flowing through it. How much voltage is applied in the circuit?
   
   GIVEN:
   R = 500 ohms
   I = 0.5 ampere
   E = ?
   
   SOLUTION:
   E = IR
   E = (0.5amp)(500 ohms)
   E = 250 volts
   
   
3. 3. A circuit containing a 250V potential causes a 0.75A of current flow. What is the resistance of the circuit?
   
   GIVEN:
   E = 250 volts
   I = 0.75 amps
   R = ?
   
   SOLUTION:
   R  =  E/I
   R = (250 volts)(0.75 amp)
   R = 333.33 ohms