In 1841, British physicistjouleIt is found that the current can generate heat when passing through the conductor. This heat is called Joule heat, and its unit isjoule（J）。
aboutImpure resistance circuitAs far as it is concerned, the general form of Joule's law is most frequently used, and the above cannot be usedPure resistanceTwo formulas in.
In addition to the general formula of Joule's law, we can also express it according to the formula I=q/t [qCharge quantity, inCoulomb(C) ] Deform the formula (applicable to all circuits):
staySeries circuitIn, because the current passing through the conductor is equal, the energizing time is also equal. According to Joule's law, the heat generated by the current passing through the conductor is proportional to the resistance of the conductor.
stayParallel circuitSince the voltages at both ends of the conductor are equal, the energizing time is also equal. According to Joule's law, the heat generated by the current passing through the conductor is inversely proportional to the resistance of the conductor.
Definition 2
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This definition is the differential definition of joule heat.In the conductive medium, the power provided by the electric field to the unit volume is consumed on the resistance of the conductive medium as joule heat in the form of heat.
Calculation formula:
P is the thermal power, dp is the power element, dV is the volume element of the conductive medium, dW is the thermal power element, dt is the time element, dF is the vector element of the electric field force, dl is the length element of the distance that the charge passes in the direction of the electric field force, dq is the charge element,
Is the charge density, E is the electric field intensity vector, v is the charge moving speed, and J is the current volume density vector.
nature
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In 1841, British physicistjoulefindCurrent carrying conductorThe heat produced in Q (called joule heat) and the square of the current IconductorThe resistance R of is proportional to the power on time t. This rule is calledJoule's law。
useInternational System of Units, whose expression is Q=I ^ 2xRt orThermal powerP=I ^ 2xR, where the units of Q, I, R, t and P are joule, ampere, ohm, second and watt in turn.
Joule's law is to design electric lighting, electric heating equipment and calculate various electrical equipmenttemperature riseImportant formula of.
In addition, Joule's law can also be transformed into Q=IRQ (the latter Q isCharge quantity, UnitCoulomb（c））。
Joule thermal solution
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1、 If the induced current is constant, it is generally solved by Joule's law
In the electromagnetic induction phenomenon, if the induced electromotive force and induced current are generated by the magnetic field change or the conductor cutting movement, and the numerical value is stable, the Joule heat of the induced current can be directly solved by the Joule law.[1]
2、 If the induced current changes aperiodically, calculate the Joule heat according to the law of conservation of energy
Joule heat
In the electromagnetic induction phenomenon, if the induced electromotive force andinduced currentIt is generated by the motion of the magnetic induction line cut by the conductor bar, but the value is non periodic, so the Joule heat of the induced current can be solved by the law of energy conversion and conservation or kinetic energy theorem.
3、 If the induced current changes periodically.Calculate joule heat from Q=I Rt (where I is the effective value of current)
In the electromagnetic induction phenomenon, ifInduced electromotive forceThe joule heat of induced current can be solved by Q=I Rt (where I is the effective value of current) if and induced current is generated by the change of magnetic field or the motion of conductor cutting magnetic induction line, and the value is periodic.
Important points
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In the problem of electromagnetic induction, most of them convert other forms of energy into electrical energy of the circuit by overcoming the work of ampere force, which is consumed by resistance and converted into joule heat energy.[2]
Joule's law is an experimental law, which has a wide range of applications.encounterCurrent heating effectFor example, toCalculated currentHeat is released when passing through a circuit;Compare a section of circuit orconductorJoule's law can be used for the amount of heat released, that is, when considering the requirements for the circuit from the perspective of current thermal effect.
fromJoule's lawThe formula shows that the heat generated by the current passing through the conductor is proportional to the square of the current intensity, the resistance of the conductor, and the power on time.
If all the work done by the current is used to generate heat.That is, according toOhm's law, with Q=I ^ 2xRt
It should be noted that Joule's law and not Joule's law are derived from Ohm's law and can only be used in the current fieldWorktakeelectric energyOnly when all of them are converted into heat energy.For electric furnaceElectric ironThese two formulas are equivalent to Joule's law for electrical appliances such as electric lamps.When analyzing and solving the heat release problem caused by the current passing through the electrical appliance, it should be, so as to reduce errors.
When using Joule's law formula for calculationphysical quantityTo correspond to the sameconductorOr the same section of circuit has the same corresponding relationship with Ohm's law.When several physical quantities appear in the question, they should be addedCorner code, to show the difference.
