Ohm’s Law – Definition, Formula, Applications

By | October 12, 2019
Ohm's Law

Ohm’s Law-

The relationship between Voltage, Current and Resistance was first discovered by the German physicist Georg Ohm in any DC electrical circuit. Georg Ohm observed the electrical current flowing through a fixed linear resistance at a constant temperature to be directly proportional to the voltage applied through it, and also inversely proportional to the resistance. This Voltage, Current and Resistance relationship forms the basis of Ohms Law and is shown below.

Ohm's Law

We can use Ohms Law to find the third missing value by understanding either two voltage, current or resistance values. Ohms Law is commonly used in equations and calculations for electronics, so it is “very important to understand and recall these formulas accurately.”

To find the Voltage, ( V )

[ V = I x R ]      

V (volts) = I (amps) x R (Ω)

To find the Current, ( I )

[ I = V ÷ R ]     

 I (amps) = V (volts) ÷ R (Ω)

To find the Resistance, ( R )

[ R = V ÷ I ]    

  R (Ω) = V (volts) ÷ I (amps)

Analyzing Ohm’s law Simple Circuits-

Let’s see how these formulas can help us evaluate basic circuits:

Ohm's Law

There is only one voltage source in the above circuit (the battery on the left) and only one source of current resistance (the lamp on the right). This makes applying Ohm’s Law very simple. When we know the values in this circuit of any two of the three quantities (voltage, current, and resistance), we can use the ohm law to calculate the third one.

We will calculate the amount of current (I) in a circuit, given voltage (E) and resistance (R) values in this first example:

Ohm's Law

Howmuch current present in this circuit?

In this second example, the amount of resistance (R) in a circuit  will be calculated, given voltage (E) and current (I) values:

Ohm's Law

How much Resistance offered by the lamp?

In the last example, the voltage supplied by a battery will be determined, given current (I) and resistance (R) values:

Ohm's Law

What is he amount of voltage offered by battery?

What to validate using Ohm’s Law?

Ohm’s Law can be used to verify circuit element static values, current levels, voltage inputs, and voltage drops. For example, if a test instrument senses a higher than normal current reading, this could mean a decrease in resistance or a rise in voltage, resulting in a high voltage situation. This might indicate a problem with the supply or circuit.

A lower than normal current measurement in direct current (dc) circuits can result in lower voltage or increased circuit resistance. Weak or loose connections, corrosion and/or damaged components are possible causes of increased resistance.

Loads on electrical current draw within a circuit Loads can be a whatever: small electrical devices, electronics, household appliances or a large engine. Most of these components (loads) are fitted with a nameplate or data sticker. These namesheets provide certificate of security and several reference numbers.

To know standard voltage and current values, technicians refer to nameplates on components. During testing, when technicians notice that custom values are not registered on their electronic multimeters or clamp meters, they can use Ohm’s Law to detect which part of a circuit fails and decide where a problem can come from.

Ohms Law Triangle-

Ohm's Law

And again, transposing the above simple Ohms Law formula for power gives us the following variations of the same equation to find the different quantities:

Ohm's Law

So for measuring electrical power in a circuit we can use three possible formulas. If the measured power is positive, the element absorbs the energy (+ P) in value for any equation, i.e. it consumes and uses power. But if the energy measured is negative, (–P) the value that the component provides or produces is a source of electrical power such as batteries and generators.

Ohms Law Pie Chart-

To help us understand a little further the relationship between the different values, we can take all the Ohm’s Law equations from above to find voltage, current, resistance and, of course, power and condense them into a basic Ohms Law pie chart for use in AC and DC circuits and calculations as shown.

Ohm's Law

We can also place the individual Ohm’s Law equations in a simple matrix table as shown for easy reference when calculating an unknown value, as well as using the Ohm’s Law Pie Chart shown above.

Ohms Law Matrix Table-

Ohm's Law

Resistors-

Ohm's Law

Resistors are one of the electrical circuit’s main components. These are made of clay and coal mixture, so not only are these good conductors, but they are also good insulators. Most resistors have four bands of colors. The first and second bands simultaneously display the value’s first and second digits. The third band is used to multiply the value digits and we are told the tolerance by the fourth band. If there is no fourth unit, the sensitivity is considered to be plus or minus 20%.

Resistance in series-

A series usually means that it is connected along a line, or in a row, or in an order. Series resistance in electronics means that the resistors are connected one after the other and there is only one direction through which the current will pass.

Ohm's Law

Laws of Series Circuits-

  • Specific resistance add up to the total resistance of the circuit
  • The current is the same at each point through the circuit.
  • Different voltages add up to the total voltage throughout the circuit.

Resistance in parallel-

A parallel circuit is structured in many different ways. Most of the wiring is performed in the practical world in parallel so that the voltage to any part of the network is the same as the voltage supplied to any other part of it.

Ohm's Law

Laws of Parallel Circuits-

  • All individual resistances ‘ reciprocals add up to the total circuit resistance’s reciprocal. 1/RT = 1/R1 + 1/R2 and 1/R3 …
  • At each point, voltage through the circuit is the same.
  • Different current draws add up to the total current draw throughout the circuit.

Also Read- Measurement of resistance

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