Power Formula

Bookmark added to your notes.
View Notes

What Do You Mean by Power?

The amount of energy utilized to perform certain work in unit time is indicated as power.

Power formula is written as, P = \[\frac{E}{t}\] (power equation)

Also, we can rewrite the power formula as, P = \[\frac{W}{t}\] (power equation)

Here, W = work done

E = Total energy consumed to accomplish work

T = Total time

We can also write the power equation as P = \[\frac{W}{\Delta t}\] 

Here, ∆t = Change in time

What is the Electrical Power Formula?

We use power factor formula in electrical circuits. We can calculate the power with the help of the following formulas. 

1st Electrical power formula: P = V × I

2nd electrical power formula = P = I2R

If we combine both first and second electrical power formula, we get:

P = V2

The above formulas have:

V = Application of a voltage across two terminals

I = Electric current passing through the circuit

R = Resistance

We use a power factor formula to calculate the power in a circuit with active voltage and current within a certain time. We also use them to find the unknown parameters of resistance, voltage, and current. ‘Watt’ is the standard metric unit applied for power.

[Image will be Uploaded Soon]

How to Find the Electrical Energy Formula?

The electrical energy formula calculation is pretty easy. It is the total work done (energy) provided by the source of e.m.f. to maintain the current flow in a circuit within a definite time. 

Electric energy: E = P × t 

= V × I × t 

= I2 × R × t 

P = V2t / R

Dimensional Formula of the Power Formula

The dimensional formula of power is, 



  • M = Mass

  • T = Time

  • L = Length

Derivation of Dimensional Formula for Power

Power (P) = Work × time-1 = Joule × second-1 …. (1)

We know that

Work (J) = N × m 

= MLT-2 × [L]


The dimensional formula of work = MLT-2 …. (2)

If we replace equation (2) in equation (1) we get,

Power (P) = Work × time-1

Or, P = [MLT-2] × [T-1]

          = MLT-3.

This is why the dimensional formula of power is represented as MLT-3.

What is the Average Power Formula?

The perfect formula that can calculate the average power formula value is:

P\[_{ave}\] = \[\frac{1}{T_{2} - T_{1}}\] \[\int_{T_{1}}^{T{2}}\] V(t)I(t)dt

How Do You Determine the Power Calculation Formula?

To calculate the power calculation formula, we have to remember three equations. They are:

  1. P (watts) = V (volts) x I (amps)

  2. P (watts) = I2 (amps) x R (Ω)

  3. P (watts) = V2 (volts) ÷ R (Ω)

This is the power triangle. 

[Image will be Uploaded Soon]

Power Consumption Formula

Before the calculation of power consumption formula, you have to make sure what the watt of the device uses per day is. You can multiply the mentioned watt value by the number of hours of its usage. 

The result you obtain is watt-hours which is the power consumption of the day.

Power consumption formula = Device Wattage (watts) x Hours Used Per Day

Tabular Form of Electricity Formula

The tabular form of electricity formulas is given hereunder:




 Current [I]

 I = Q / t

Q = Charge

t = time taken

 Amperes (A)

 Voltage [V]

V = E / Q


V = W / Q

E = Energy

W = Work done

 Volts (V)

 Resistance [R]

 R = ρ*l / A

ρ = Resistivity,

l = length,

A = Area


 R = V / I

 Ohm (Ω)

 Power [P]

 P = VI

 Watts (W)

 Conductivity [σ]

 sigma = 1 / ρ

 Siemens per meter (S/m)


We all know about energy. Energy is the term that is used to explain the capacity to perform any kind of work. This content is sufficient enough to guide you regarding different formulae associated with power. 

FAQ (Frequently Asked Questions)

Q1. An Electric Lamp has Been on for the Last 4 Hours. The Amount of Current is 0.6 A. Find the Charge.

Ans: Charge Q = I × t

= 0.6 × [4 * 3600]

Q = 8640 C

Q2. Find the Current in a Circuit, if the Voltage is 210 V and the Resistance is 70 Ohms.

Ans: Current I = V / R

= 210 / 70 

I = 3A

Q3. What is the Power Used to Produce 400 J Energy within 20 Seconds?

Ans: Power = W / t = 400 J / 20 s = 20 Watts