Electric Power Formula

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Electricity is needed by the community for various purposes. This was an invention that changed world civilization. When using electricity, there is a term power, especially if you check the meter from PLN (in Indoensia).

The numbers listed can be data for the application of the electric power formula. If you know the formula, you will understand how to use electricity and electronic devices which is correct and safe.

Definition of Electric Power


Understanding Power is the rate of transfer rate of electrical energy present at electronic circuit As a result of changes in effort and electric charge every unit of time. Examples of tools that can deliver electrical power are electric generators (for large scale) and electric batteries (for small scale).

In addition to the two electronic devices above, electrical power is also commonly used in the business sector and households that usually utilize electricity supply from the Indonesia government electric power network (PLN).

Electrical power usage is measured by PLN using electricity meters, which maintain the total electrical energy distributed to consumers. Here are the basic concepts regarding electrical power.

Basic Concept of Electric Power:

  • Energy per unit time

Electric power is also known as power where it is energy used to run electrical components so that they function according to their purpose in a certain time.

Power can also be interpreted as an effort to move or do something per unit of time. In physics, power has no direction so calculations do not need to think about pluses and minuses.

  • Use of current and voltage

As reported by the site wikipedia.org, there is another concept of electrical power is the capacity or power needed to run a electrical circuit. Power like this comes from potential differences, electric charge, and units of time. This potential causes a difference in voltage and electric charge that moves is called current.

Electric Power Unit


The unit of electrical power is watts (W), where  1 Watt = 1 Joule / second. According to the International Unit, electric power is denoted by the symbol letter P which in the calculation has units of kg·m²/s³.

To be clearer in understanding electrical power units according to SI (International Standards), here we describe a table containing symbols and units of electrical power equipped with other electrical units.

Quantity Symbol Unit
Electric Power P watt (W) = J/s kg·m²/s³
Frequency f hertz (Hz) 1/s
Electric Charge Q coulomb(C) = A·s A·s
Electric Current I ampere (A) = Q/s A
Resistance R ohm (Ω) = V/A kg·m²A²·s³
Voltage V volt (V)= W/A kg·m²/A·s³
force F newton (N) kg·m/s²
Pressure P pascal (Pa) = N/m² kg/m·s²
energy E work joule (J) = N·m kg·m²/s²
capacitance C farad (F) = C/V = A·s/V = s/Ω A²·s4/kg·m²
inductance L henry (H) = Wb/A = V·s/A kg·m²/A²·s²
conductance G siemens(S) = A/V A²·s³/kg·m²
magnetic flux Φ weber (Wb) = V·s kg·m²/A·s²
flux density B tesla (T) = Wb/m² = V·s/m² kg/A·s²

Table Via : www.sengpielaudio.com

Difference between Watt (W) and Horsepower (HP):

In addition to having an international unit of Watt (W), in certain cases electric power also has another unit, namely Horsepower (HP). To make it easier to understand, here we attach the difference in wattage (W) units with Horsepower (HP) on electric power:

  • Watt Unit

The unit of electrical power that is known to many people is the watt with the symbol W. For power 1000 watts becomes kilowatts and so on following the standard system. Watt came from the inventor of the steam engine from England. Actually, the wattage is derived from joules per second based on the power formula.

  • Horsepower Unit

Another unit is horsepower which is often used in motorcycles, cars, ships, airplanes, and engines. The calculation of one horsepower is equal to 746 watts. Such a conversion system is useful so that engine performance and performance are easier to measure. The term horsepower means horsepower comes from the use of the animal to pull the carriage.

Electric Power Formula


According to international units, the formula for calculating electric power  is P = V x I, where P is Electric Power (W), V is Electric Voltage (V), and I is Electric Current (A).

If we refer to Ohm’s Law, we see that V = I.R, thus there is another form of electrical power formula for a resistor. Power has units of Watts, then it is important for you to know thatWatts = Joules per second. (1 W = 1 J/s). This is where derivatives appear Electric Power Formula that is:

P = I2R P = V2


P is the electrical power (W)

V refers to the voltage difference (V= J/C)

I is the electric current (A = C/s)

R refers to resistance (Ω = V/A)

To make it easier to calculate the electric power formula above, here we also describe a table containing multiples of Watt units that you can see:

Current Name Abbreviation
10-15 watts femtowatts Fw
10-12 watts picowatts Pw
10-9 watts nanowatts nW
10-6 watts microwatts μW
10-3 watts milliwatts Mw
Watts Watts W
103 watts kilowatts Kw
106 watts Megawatts MW

The electric power formula is derived from the concept and definition of power that has been known. Check out the following list to find out more details.

  • Power Formula as energy use

P = E/T or P = VQ/ T

In general, power can be calculated by means of the amount of work or energy per unit time. This concept applies to any type and variant of power, including electricity. The symbol of power is P, which is a representation of the word power.

  • Voltage and current

P = V.i

Calculating the next electrical power based on the second concept, namely power is the use of voltage and current so you only need to multiply the two variables so that P = Vi.

  • Electrical resistance

I = V/R then P = VI

The formula in number 2 can be derived by voltage or current substitution based on the resistance formula. For example, you want to know the power in  a particular resistor where the current value is known.

Change V to Ri so that the power formula is the squared resistance times the current. Similarly, you can substitute I for V/R and substitute it for the power formula.

Example of Calculating Electric Power Problem

To make it easier to understand the electric power formula above, here we review examples of calculating electrical power problems complete with answers and discussions for your practice.

  1. A 9V battery is connected to a resistor that has a resistance value of 10. What is the current and power across the resistor?


I = V/R = 9/100 = 0.9 A

P = VI = 9 × 0.9 = 8.1 J/s or 8.1 W

So the electrical power that crosses the resistor above is 8.1 Watts

  1. A resistor has a potential difference value of 24.0 V and emits thermal energy. The rate of heat energy produced by the resistor is 16.0 W. What is the resistance value?

Discussion :


So the resistance value on the resistor above is 36.0 Ω

  1. If the cost of electricity in your home area is 12 rupiah per kWh, what is the total cost of using a 60-W LED lamp for 1000 hours if the bulb costs 25 rupiah?


To find the cost of using a lamp, we first find the energy used in kilowatts / hour and then multiply it by the cost per kilowatt / hour.

E = Pt = (60 W)(1000 hours) = 60,000 W hours

In kilowatt-hours, these are

E = 60.0 kW hours.

The total cost of electricity consumption is:

Cost = (60.0 kW hours) x (0.12/kW hours) = 7.20 rupiah

The total cost will be Rp. 7.20 for 1000 hours (about one and a half years with 5 hours of use per day).

  1. If the current and voltage in the electrical circuit are given 2.5A and 10V respectively. What is the electrical power?

I = 2.5A and V = 10V
The electric power formula is :
P = VIP = 10 × 2.5 = 25 watts

  1. Calculate the electric power in an electrical circuit that has a resistance value of 3Ω and a Current of 4A!

I = 4A and R = 3Ω
The electric power formula is :
P = I2R

P = 42×3P = 16×3 = 48 watts

Also Read: Get to know Thermal Overload Relay, Symbols, Functions, How It Works

Order of Electric Power in Indonesia

The order of electrical power or distribution voltage systems in Indonesia varies greatly, generally those used in Indonesia have a capacity of 3 KV, 6 KV, 7 KV, 9 KV, 11.5 KV, 20 KV and 24 KV.

For the standards used, PLN itself generally uses 6 KV, 12 KV, 20 KV, and 24 KV only. Others are distributed for the needs of specific industrial industries.

Now for those of you who need information about the order of PLN customer meters ranging from household needs (250 VA, 1 Phasa), to office industry needs (630 KVA, 3 Phasa), please see the table below:

No. Installed Power (Volt Ampere) MCB/MCCB Limiter (Amperes)
1 250 1 X 1.2
2 450 1 X 2
3 900 1 X 4
4 1,300 1 X 6
5 2,200 1 X 10
6 3,500 1 X 16
7 4,400 1 X 20
8 5,500 1 X 25
9 7,700 1 X 35
10 11,000 1 X 50
11 13,900 1 X 63
12 17,000 1 X 80
13 22,000 1 X 100
14 3,900 3 X 6
15 6,600 3 X 10
16 10,600 3 X 16
17 13,200 3 X 20
18 16,500 3 X 25
19 23,000 3 X 35
20 33,000 3 X 50
21 41,500 3 X 63
22 53,000 3 X 80
23 66,000 3 X 100
24 82,500 3 X 125
25 105,000 3 X 160
26 131,000 3 X 200
27 147,000 3 X 225
28 164,000 3 X 250
29 197,000 3 X 300
30 233,000 3 X 335
31 279,000 3 X 425
32 329,000 3 X 500
33 414,000 3 X 630
34 526,000 3 X 800
35 630,000 3 X 1000

Then regarding the electrical power distributed to middle and large class consumers, PLN follows the transformer capacity and also the load on consumer substations (GI). Among the transformers / transformers used are as follows:

No. Types of transformers Capacity
1 3 Phase Transformer 25 kVA 20kV/ 400V
2 3 Phase Transformer 50 kVA 20kV/ 400V
3 3 Phase Transformer 100 kVA 20kV/ 400V
4 3 Phase Transformer 160 kVA 20kV/ 400V
5 3 Phase Transformer 200 kVA 20kV/ 400V
6 3 Phase Transformer 400 kVA 20kV/ 400V
7 3 Phase Transformer 500 kVA 20kV/ 400V
8 3 Phase Transformer 630 kVA 20kV/ 400V
9 3 Phase Transformer 1000 kVA 20kV/ 400V
10 3 Phase Transformer 1250 kVA; 20kV/400V
11 3 Phase Transformer 1500 kVA; 20kV/400V
12 3 Phase Transformer 1750 kVA; 20kV/400V
13 3 Phase Transformer 2000 kVA; 20kV/400V
14 3 Phase Transformer 2500 kVA; 20kV/400V
15 3 Phase Transformer 3150 kVA; 20kV/400V

Source : https://electric-mechanic.blogspot.com/

Examples of Electric Power Application



  • PLN Electricity (Indonesia)

PLN electric power has certain limits, for example 450W to 4400W electricity. On the meter, you will see a number that shows the maximum voltage such as 220V then the limit of the current.

PLN electricity can be increased so that the power is greater, for example from 450 to 900 or 1300. To do this, you need to pay the cost of adding electricity

  • Electronic devices

Electrical and electronic devices also have information about power. For example, 220V/2A means that the maximum voltage limit is 220V and the current value is 2A. To find out the power, you multiply the two values so that it becomes 440 watts. That is, the tool is able to accommodate a maximum voltage of 220V and uses a current of 2A.

  • Automotive and machinery industry

Electric power is also found in vehicles and engines. As long as it still uses electricity, the term power or power is still needed. Of course, the system and its application follow their respective fields.

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