What is Ohm's Law?.
"Ohm's Law states that the amount of current flowing in a circuit made up of pure resistance is directly proportional to the electromotive forces impressed on the circuit and inversely proportional to the total resistance of the circuit". The basic formulas are

( For the Voltage    ( V )  =   I   x   R )        ( For the Current in amps    ( I )   =   V   /   R )        ( For the Resistance in ohms    ( R )   =   V  /   I )

    "Question"   When would you use Ohm's Law.
Lets take an example of a large 3.4KW storage heater which is no longer getting as hot as it did when it was new. How do I find out if any elements have gone faulty?

    Answer.
The load of the storage heater is 3.4KW or 3400 watts and the supply voltage is 240 volts. Calculate the resistance of the heater in ohms using the formula

( Resistance = Volts 2 / Power in watts) which would be   R  =  240  x  240 / 3400  =  16.94 ohms.

Measure the storage heaters resistance in ohms with a meter. Compare the calculated resistance value with the actual reading value obtained with the meter. They should be the approximately same. If they are not, then one or more of the elements could be open circuit and therefore faulty.

The reading for all four good elements in the heater would be 16.94ohms
The reading for only three good element in the heater would be 22.588ohms
The reading for only two good element in the heater would be 33.88ohms
The reading for only one good element in the heater would be 67.76ohms

As there are 4 elements in the heater, each elements is a 4th of the rated value of 3400 watts which is 850 watts with a resistance of 67.76ohms

Try the calculator below. Enter 3400 in the watts box and 240 into the volts box. Press "Calculate" to find the resistance and current of the heater. Please note that all boxes must be reset to "0" before the calculation. The result shows that the resistance of the storage heater with all four elements in good working order is 16.94ohms and the current is 14.16amps.

Enter any two known values and press "Calculate" to solve the others. After each calculation you must press the "Reset" to calculate another value.

    Enter any two known values into the correct box below and press the Calculate button    

    "Please Note". You must press the Reset Button to set all boxes to 0 before each new calculate.

Useful formulas for calculating Current, Power, Resistance and Voltage.

    Calculation for Current ( I )             I   =   P / V              I   =   Square Root of (P / R)              I   =   V / R