Some Important Formulas of Electrical Engineering

Electric Power Formulas:

P = V I         (1a)

P = R I²         (1b)

P = V²/ R         (1c)

where

P = power (watts, W)

V = voltage+ (volts, V)

I = current (amperes, A)

R = resistance (ohms, Ω)

Electric Current Formulas:

I = V / R         (2a)

I = P / V         (2b)

I = (P / R)^1/2   (2c)

Electric Resistance Formulas:

R = V / I         (3a)

R = V²/ P        (3b)

R = P / I²         (3c)

Electrical Potential Formulas - Ohms Law:

Ohms law can be expressed as:

V = R I         (4a)

V = P / I         (4b)

V = (P R)^1/2         (4c)

Example - Ohm's law:

A 12 volt battery supplies power to a resistance of 18 ohms.

I = (12 V) / (18 Ω)

    = 0.67 (A)

Electrical Motor Formulas:

Electrical Motor Efficiency

μ = 746 P_hp / P_{input_w}         (5a)

where

μ = efficiency

P_hp = output horsepower (hp)

P_{input_w} = input electrical power (watts)

or alternatively

μ = 746 P_hp / (1.732 V I PF)         (5b)

Electrical Motor - Power

P_3-phase = (V I PF 1.732) / 1,000         (6)

where

P_3-phase = electrical power 3-phase motor (kW)

PF = power factor electrical motor

Electrical Motor - Amps

I_3-phase = (746 P_hp) / (1.732 V μ PF)         (7)

where

I_3-phase = electrical current 3-phase motor (amps)

PF = power factor electrical motor

Opp amp

Introduction   :
The op amp is one of the basic building blocks of linear design. In its classic form it consists of two input terminals, one of which inverts the phase of the signal, the other preserves the phase, and an output terminal. The standard symbol for the op amp is given in Figure. This ignores the power supply terminals, which are obviously required for operation.  
Figure :  Standard op amp symbol
The name “op amp” is the standard abbreviation for operational amplifier. This name comes from the early days of amplifier design, when the op amp was used in analog computers. (Yes, the first computers were analog in nature, rather than digital). When the basic amplifier was used with a few external components, various mathematical “operations” could be performed. One of the primary uses of analog computers was during WWII, when they were used for plotting ordinance trajectories.