Ohm's Law and Power

Ohm law is one of the most used methods for analyzing any DC electrical circuit. The relationship between Voltage, Current and Resistance in any DC electrical circuit was first discovered by German physicist Georg Ohm.

Georg Ohm found that at a constant temperature, the electric current flowing from a constant linear resistance is directly proportional to the applied voltage, as well as inversely proportional to the resistance.This relationship between Voltage, Current and Resistance forms the basis of ohm law.

Voltage (V) = Current (I) x Resistance (R)

Knowing any two values of voltage, current or resistance quantities, we may use ohm law to find the third missing value.You can also make your calculations with our calculation page here.

The Ohm Actis widely used in electronic formulas and calculations, so "it is very important to understand and remember these formulas correctly".

To find the voltage, use the ( V )

[ V = I x R ] V (volt) = I (amperage) x R (Ω)

To find the current, use the ( I )

[ I = V ÷ R ] I (amperage) = V (volt) ÷ R (Ω)

To find resistance, use ( R )

[ R = V ÷ I ] R (Ω) = V (volt) ÷ I (amperage)

It is sometimes easier to remember this Ohm law relationship using pictures.Here, the three amounts of V, I and R are placed in a triangle(called the Ohm Law Triangle), which gives tension with current at the top and resistance below.This arrangement represents the actual position of each quantity within the Ohm law formulas.

Ohm Law Triangle

We can write the above standard Ohm Law equation in different combinations:

Then, using the Ohm Law, we can see that a voltage of 1V applied to a resistance of 1Ω will cause a current of 1A to flow, and the larger the resistance value, the less current will flow for a given applied voltage.Any electrical device or component that complies with the "Ohm Act", i.e. the current flowing through it, is proportional to the voltage on it, such as resistors or cables (I α V), which is inherently called "Omik".

Electrical Power in Circuits

Electric Power , ( P ) is the rate at which energy is absorbed or produced in a circuit.An energy source, such as voltage, will generate or transmit power while the connected load absorbs it.For example, bulbs and heaters absorb electrical power and convert it into heat, light or both.The higher their value or rating in watts, the more electrical power they are likely to consume.

The quantity symbol of power is P and is the current multiplication of the voltage, and the unit of measure is Watt ( W ).Pre-inserts are used to indicate various multiples or lower multiples of one watt, for example: milliwatts ( mW = 10 -3 W ) or kilowatts ( kW = 10 3 W ).

Then, using the Ohm law and changing the V, I, and R values, the electric power formula can be found as follows:

To find power (P)

[ P = V x I ] P (watts) = V (volt) x I (amperage)

In addition:

[ P = V 2 ÷ R ] P (watts) = V 2 (volt) ÷ R (Ω)

In addition:

[ P = I 2 x R ] P (watts) = I 2 (amperage) x R (Ω)

Again, these three quantities can be placed in a triangle called a Power Triangle, which has power at the top and current and voltage at the bottom.Again, this arrangement represents the actual position of each quantity within the Ohm law power formulas.

Power Triangle

and again, transposing the above basic Ohm Act equation for power gives us the following combinations of the same equation to find various individual quantities:

So we can see that there are three possible formulas for calculating the electrical power in a circuit.If the calculated power for any formula is positive and (+P) is positive, the component absorbs power, that is, it consumes or uses power.However, if the calculated power is negative (–P), the component generates power, that is, it is an electrical power source such as a battery and generator.

Electric Power Rating

Electrical components are given a "power rating" in watts, indicating the maximum speed at which the component converts electrical power into other forms of energy, such as heat, light or motion.For example, a resistance of 1/4W, a 100W bulb, etc.

Electrical devices convert one form of power into another.For example, an electric motor converts electrical energy into a mechanical force, while an electric generator converts mechanical force into electrical energy.A light bulb converts electrical energy into both light and heat.

Also, we now know that the power unit is WATT , but some electrical devices, such as electric motors, have a power rating in the old "Horsepower" or hp measurement.The relationship between horsepower and wattage is given as follows: 1hp = 746W.For example, a two-horsepower engine has a value of 1492W, (2 x 746) or 1.5kW.

Ohm Law Pie Chart

To help us understand a little more about the relationship between various values, we can take all ohm law equations from above to find voltage, current, resistance and of course power, and concentrate them on a simple Ohm Law pie chart for use.

Ohm Law Pie Chart

In addition to using the Ohm Law Pie Chart shown above, we can also put individual Ohm Law equations in a simple matrix table, as shown for easy reference when calculating an unknown value.

Ohm Law Matrix Table

OhmLaw Matrix Table

Ohm Law Question Example 1

Find Voltage (V), Current (I), Resistance (R) and Power (P) for the circuit shown below.

Voltage [ V = I x R ] = 2 x 12Ω = 24V

Current [ I = V ÷ R ] = 24 ÷ 12Ω = 2A

Resistance [ R = V ÷ I ] = 24 ÷ 2 = 12 Ω

Power [ P = V x I ] = 24 x 2 = 48W

The power in an electrical circuit is only available when both voltage and current are present.For example, in an open-circuit state, there is no current flow, although the supply voltage is present I = 0 (zero), so V * 0 = P = 0.Similarly, if we have a short circuit state, there is a current flow but there is no voltage V = 0 , so the power spent in the circuit is 0 * I = 0.

Since the electric power is the product of V*I, the power spent in a circuit is the same regardless of whether there is high voltage and low current or low voltage and high current flow in the circuit.

Electrical Energy in Circuits

Electric Power is capable of doing business and the business or energy unit is joule (J).Electrical energy is the product of power multiplied by the length of time consumed.So if we know how much power is consumed in Watts and the amount of time it is used in seconds, we can find the total energy used in watt-seconds.In other words, Energy = power x time and Power = voltage x current.Therefore, electrical power is related to energy, and the unit given for electrical energy is watt-seconds or joule.

Energy = Power (W) x Time (s)

Electrical power can also be defined as the rate at which energy is transferred.If a joule work is absorbed or given at a constant speed of one second, the corresponding power will be equivalent to one watt, so the power can be defined as "1 Joule/s = 1Watt".Then we can say that one watt equals one joule per second, and electric power can be defined as the speed at which it does business or transfers energy.

Electrical Power and Energy Triangle

or to find various individual quantities:

We've previously said that electrical energy is defined as watts per second or joule.Although electrical energy is measured in Joule, it can become a very large value when used by a component to calculate the energy consumed.

For example, if a 100 watt bulb is left "ON" for 24 hours, the energy consumed is 8,640,000 Joule (100W x 86.400 seconds), so 10 6 J is used instead of kilojul (kJ = 10 3 J ) or megajul (prefixes such as MJ = ), and in this simple example the energy consumed will be 8.64MJ (mega-joule).

However, it is much easier to express electrical energy in Kilowatt-hours than to use joule, kilojul or megajul.

If the consumed (or generated) electrical power is measured in watts or kilowatts (thousand watts) and time is measured in hours, not seconds, the unit of electrical energy will be kilowatt-hour (kWh).Then our 100 watt bulb above will consume 2,400 watt hours or 2.4kWhr.

1 kWh is the amount of electricity used by a device worth 1000 watts in an hour and is often referred to as the "Electrical Unit".This is what we buy from our electricity suppliers when we receive our invoices as consumers, measured by the electricity meter.

Kilowatt-hour is the standard unit of energy used by the electricity meter in our homes to calculate the amount of electrical energy we use and therefore how much we pay.So if you turn on a heating element worth 1000 watts and leave it on for 1 hour, you will consume 1 kWh of electricity.If you turn on two power tools with 1000 watts each for half an hour, the total consumption will be exactly the same amount of electricity – 1kWh.

So consuming 1000 watts per hour uses the same amount of power as 2000 watts (twice) for half an hour (half the time).Then a 100 watt bulb must remain on for a total of 10 hours (10 x 100 = 1000 = 1 kWh) to use 1 kWh or one unit of electrical energy.

Now that we know what the relationship between voltage, current and resistance in a circuit is, in the next tutorial on DC Circuits we will look at the Standard Electrical Units used in electrical and electronic engineering to allow us to calculate and see these values. each value can be represented by multiples or lower floors of the standard unit.