Ohm's law states that the potential difference or Voltage drop V between the ends of a conductor (for example, a resistor R) and the current (I), flowing through R are proportional at a given temperature:

 

The ammeter measures the current flowing through the reisitor.

The voltmeter measures the voltage across the resistor.

 

 

Assume that the meters are ideal and they have no effect on the circuit ...

  • No current flows through an ideal voltmeter.
  • No voltage is lost across an ideal ammeter.

 

 

R = V / I

R = resistance in Ohms

V = Voltage (potential difference) in Volts.

I = current in Amps.

 

This triangle helps some people to remember that

R = V / I

V = I R

I = V / R