Common units and formulas for electric power people and conversion

Electric work: the work done by a certain circuit through a certain circuit for a period of time.

W stands for work, and the unit of work is: Joule (J)

W=P*t

P---power (unit: watt w)

t---time (unit: second s)

W=U*I*t

U---voltage (unit: volt V)

I---current (unit: An A)

t---time (unit: second s)

W=I ² *R*t

I---current (unit: An A)

R---resistance (unit: ohms)

t---time (unit: second s)

W=U ² /R*t

U---voltage (unit: volt V)

R---resistance (unit: ohms)

t---time (unit: second s)

Power: refers to the work done by the object in unit time

P represents power, and the power unit is: watt (W)

P=W/t

W---electric work (unit: joule j or kWh kWh)

t---time (unit: second s)

P=U*I

U---voltage (unit: volt V)

I---current (unit: An A)

P=U ² /R (only for purely resistive circuits)

U---voltage (unit: volt V)

R---resistance (unit: ohms)

P=I ² *R (only for purely resistive circuits)

I---current (unit: An A)

R---resistance (unit: ohms)

Charge: The amount of electricity charged by an object or a particle that makes up an object. It is the algebraic sum of the elemental charge in an object or system.

Q represents charge, and the unit of charge is: Coulomb (C)
Current: refers to the directional movement of charge

I represents current, the unit of current is: Ampere (A)

Current density: the amount of electricity passing through a unit area per unit time. The direction vector is the normal vector of the corresponding section of the unit area, which is determined by the direction of the positive charge passing through the section.

J represents the current density, and the unit of the current is: ampere/square meter A/m2

Voltage: potential potential difference.

U represents voltage, and the voltage unit is: Volt (V)

U=I*R

I---current (unit: An A)

R---resistance (unit: ohms)

U=P/I

P---power (unit: watt w)

I---current (unit: An A)

U=I*ρ*L/S

I---current (unit: An A)

ρ---resistivity (unit: ohm·mΩ·m)

L---object length (unit: m)

S---section area of ​​the object (unit: square meter m2)

Capacitance: refers to the amount of charge stored at a given potential difference

F represents the capacitance, the unit of capacitance is: Farah (F)

Capacitance: Determines the ratio of the capacitance between the two electrodes of a capacitor and the vacuum capacitance of the same board when only the insulating oil is filled.

Resistance: to indicate the size of the conductor blocking current

R represents the resistance, and the unit of the resistance is: ohm (Ω)

R=U/I

U---voltage (unit: volt V)

I---current (unit: An A)

R=ρ*L/S

ρ---resistivity (unit: ohm·mΩ·m)

L---object length (unit: m)

S---section area of ​​the object (unit: square meter m2)

Conductance: indicates the strength of a certain type of conductor transmission current

G represents the conductance of the object. The unit of conductance is: Siemens (S) or ohm (Ω)

G=1/R

R---resistance (unit: ohms)

G=I/U

I---current (unit: An A)

U---voltage (unit: volt V)

Resistivity: The resistance of a wire made at a normal temperature (at 20 ° C) with a length of 1 m and a cross-sectional area of ​​1 mm 2 made of a certain material

ρ represents the resistivity, and the unit of resistivity is: ohm·meter (Ω·m)

ρ=1/κ

κ---resistivity (unit: Siemens / m S / m)

ρ=R*S/L

S---cross-sectional area (unit: square meter m2)

R---resistance (unit: ohms)

L---the length of the wire (unit: m)

ρ=E/J

E---Electrical field strength (unit: cow / bank N / C)

J---current density (unit: ampere/square meter A/m2)

ρ=ρ ₀ *(1+a*t)

Resistivity at ρ ₀ ---0 ° C (unit: ohm·m Ω·m)

t---Celsius temperature (unit: Celsius)

a---resistivity temperature coefficient

Conductivity: refers to the product of this amount and the electric field strength in the medium equal to the conduction current density. Conductivity is the reciprocal of resistivity.

κ (Greek letter is not the letter K) indicates conductivity, and the unit of conductivity is: Siemens / meter (S / m)

κ=1/ρ

ρ---resistivity (unit: ohm·mΩ·m)

Inductance: When the current through the closed loop changes, an electromotive force will appear to resist the change of current.

L represents the inductance, the unit of inductance is: Henry (H)

Reactance: The blocking effect of capacitors and inductors on the AC in the circuit is called reactance.

X represents the reactance, and the unit of reactance is: ohm (Ω)

X=X _L X _C

X _L --- the inductive reactance of the circuit

X _C --- Circuit capacitive reactance

Inductive reactance: Generally, because of the changing electromagnetic field generated by an inductive circuit (such as a coil) in the circuit, a corresponding electric power that hinders the flow of current is generated. The greater the current change, that is, the larger the circuit frequency, the greater the inductive reactance; the inductive reactance causes a phase difference between the current and the voltage.

X _L =ωL

ω---angular frequency (unit: radians / rad / s per second)

L---inductance (unit: Henry H)

X _L =2*Ï€*f*L

f---frequency (unit: Hertz Hz)

L---inductance (unit: Henry H)

Capacitive reactance: The higher the frequency of the alternating current, the smaller the capacitive reactance, that is, the smaller the blocking effect of the capacitor. The capacitive reactance also causes a phase difference between the current and the voltage across the capacitor.

X _C =1/(ω*C)

ω---angular frequency (unit: radians / rad / s per second)

C---capacitor (unit: Farah F)

X _C =1/(2*Ï€*f*C)

f---frequency (unit: Hertz Hz)

C---capacitor (unit: Farah F)

Angular frequency---In the simple harmonic motion, the frequency is 2Ï€ times the angular frequency.

ω represents the angular frequency, and the angular frequency unit is: radians/second (rad/s)

ω=2*π*f