Elektromagnit induksiya qonuni

**Elektromagnit induksiya qonuni** yoki **Faradayning induksiya qonuni**

Modomiki zarralarning kinetik energiyasi oʻzgarishi ularning tezligi bilan bogʻlangan ekan, biz darhol harakat tezligi va elektromagnit maydon kuchlanganliklari orasidagi bogʻlanishni ifodalovchi quyidagi formulaga murojaat qilamiz:
: 
\textrm{rot}\textbf{H}=4\pi\frac{\rho\textbf{u}}{c}+\frac{1}{c}\dfrac{\partial \textbf{E}}{\partial t}


Mazkur tenglamadan tok zichligini aniqlaymiz:
: 	\rho\textbf{u}\frac{c}{4\pi}\textrm{rot}\textbf{H}-\frac{1}{4\pi}\dfrac{\partial\textbf{E}}{\partial t};(1)

Bu tenglamaning ikki tomonini \textbf{E} vektorga skalyar koʻpaytirib chiqamiz:
: 	(\rho\textbf{uE})=\frac{c}{4\pi}\left(\textbf{E}\textrm{rot}\textbf{H}\right)-\frac{1}{4\pi}\left(\textbf{E}\dfrac{\partial \textbf{E}}{\partial t}\right) ;(2)

Har qanday \textbf{a} vektor uchun quyidagini yozish mumkin:
: \dfrac{\partial a^{2}}{\partial t}=\dfrac{\partial}{\partial t}(\textbf{aa})=\left(\textbf{a}\dfrac{\partial a}{\partial t}\right)+\left(\dfrac{\partial a}{\partial t}\textbf{a}\right)=2\left(\textbf{a}\dfrac{\partial a}{\partial t}\right)

demak,
: 
	\left(\textbf{E}\dfrac{\partial \textbf{E}}{\partial t}\right)=\frac{1}{2}\dfrac{\partial \textbf{E}^{2}}{\partial t},
:  \left(\textbf{H}\dfrac{\partial\textbf{H}}{\partial t}\right)=\frac{1}{2}\dfrac{\partial\textbf{H}^{2}}{\partial t}
	

Maydon nazariyasidan maʼlumki, vektor koʻpaytmaning divergensiyasi uchun \textrm{div} [\textbf{EH}]=(\textbf{H}\ \textrm{rot}\ \textbf{E})-(\textbf{E} \textrm{rot} \textbf{H}), demak, (\textbf{E} \textrm{rot} \textbf{H})=(\textbf{H}\ \textrm{rot} \textbf{E})-\textrm{div}\ [\textbf{EH}], demak, (\textbf{E}\  \textrm{rot}\textbf{H})=(\textbf{H}\  \textrm{rot}\textbf{E})-\textrm{div}[\textbf{EH}]. Endi (2)-tenglamani quyidagicha yozib olaylik:
: 	(\rho\textbf{uE})=\frac{c}{4\pi}(\textbf{H}\ \textrm{rot}\textbf{E})-\frac{c}{4\pi}\textrm{div}[\textbf{EH}]-\frac{1}{8\pi}\dfrac{\partial}{\partial t}E^{2}+\frac{1}{4\pi}\left(\textbf{H}\dfrac{\partial\textbf{H}}{\partial t}\right)
	-\frac{1}{8\pi}\dfrac{\partial}{\partial t}H^{2}
	

	yoki
: 
	(\rho\textbf{uE})=\frac{1}{4\pi}
	\left(\textbf{H},c\ \textrm{rot}\textbf{E}+
	                   \dfrac{\partial\textbf{H}}
	                   {\partial t}\right)
	                   -\dfrac{\partial}{\partial t}\left[
	                   \frac{1}{8\pi}E^{2}+
	                   \frac{1}{8\pi}H^{2}	                   
	                   \right]
	                   -\textrm{div} \frac{c}{4\pi}\left[\textbf{EH}\right]


Mazkur ifodani zaryadlar va elektromagnit maydonlar joylashgan ixtiyoriy hajm boʻyicha integrallab chiqamiz:

\int (\rho\textbf{uE})dV=
\frac{1}{4\pi}\int
\left(
\textbf{H}, c\ \textrm{rot}\textbf{E}+
\dfrac{\partial \textbf{H}}{\partial t}
\right)
+\oint\left(
\frac{c}{4\pi}
[\textbf{EH}],d\sigma
\right)
+\int(\rho\textbf{uE})dV=\frac{1}{4\pi}\int\left(
\textbf{H},c\ \textrm{rot}\textbf{E}+\dfrac{\partial \textbf{H}}{\partial t}
\right) dV


Integrallash hajmining oʻzgarmasligi tufayli va Gauss-Ostrogradskiy formulasi asosida yuqoridagi ifoda shunday yoziladi:
: 
	\frac{d}{dt}\int\left(\frac{E^{2}}{8\pi}+\frac{H^{2}}{8\pi}\right)dV+
	\oint\left(\frac{c}{4\pi}\ [\textbf{E,H}],d\sigma\right)
	+\int(\rho \textbf{uE})dV=\frac{1}{4\pi}
	\int\left(\textbf{H}, c\ \textrm{rot}\ \textbf{E}+\dfrac{\partial \textbf{H}}{\partial t}\right)dV ;(3)


Shu topilgan natija gʻoyat katta ahamiyatga ega. Agar soʻnggi tenglikning chap tomonidagi birinchi had hajmdagi elektromagnit maydon energiyasining vaqt birligidagi oʻzgarishi, ikkinchi had hajm chegaralangan yopiq sirtdan vaqt birligida oʻtayotgan elektromagnit energiya oqimi, uchinchi had elektromagnit maydon taʼsiri natijasida hajmdagi zarralar kinetik energiyasining vaqt birligidagi oʻzgarishi deb qabul qilinsa, (1) va (3) ga asosan energiya saqlanish qonuni quyidagi shaklni oladi:
: 
\dfrac{d}{dt}\int\left(\frac{E^{2}}{8\pi}+\frac{H^{2}}{8\pi}\right)dV + \oint\left(\frac{c}{4\pi}[\textbf{E H}], d\sigma \right)+
\int(\rho \textbf{u E}) dV = 0 ;(4)

Bu muhim formula elektrodinamikada energiya saqlanish qonunini ifodalaydi.

Energiya saqlanish qonunining (4) ifodasiga muvofiq, (3) dan koʻramizki,
: 
\int\left(\textbf{H}, c\ \textrm{rot} \textbf{E} + \dfrac{\partial H}{\partial t} \right)dV = 0

Integrallash hajmi ixtiyoriy qilib olingan edi, demak,
: \left(\textbf{H}, c\ \textrm{rot} \textbf{E} + \dfrac{\partial H}{\partial t} \right) = 0

Bu natija har qanday **E** va **H** vektorlar uchun toʻgʻridir, demak
: 
c\ \textrm{rot}\textbf{E} + \frac{\partial H}{\partial t} = 0
yoki
: \textrm{rot} \textbf{E} = -\frac{1}{c}\frac{\partial H}{\partial t}


Bu ifoda elektrodinamikaning asosiy differensial tenglamalaridan biridir. Mazkur differensial tenglama magnit maydon oʻzgarishi natijasida uyurmaviy elektr maydon paydo boʻlishi qonunini ifodalaydi. Bu qonun *elektromagnit induksiya qonuni* deb ham ataladi.

## Yana qarang
* Elektromagnit maydon energiyasi
* Magnit maydonining manbasizligi
* Elektromagnit impuls oqimining zichlik tenzori

## Adabiyotlar
* *R.X.Mallin*, Klassik elektrodinamika, Oʻqituvchi, T., 1974
## Havolalar
* A simple interactive Java tutorial on electromagnetic induction
* R. Vega ''Induction: Faraday’s law and Lenz’s law'' — Highly animated lecture
* Notes from Physics and Astronomy HyperPhysics at Georgia State University
* Faraday’s Law for EMC Engineers
* Maxwell, James Clerk (1881), ''A treatise on electricity and magnetism, Vol. II'', Chapter III, § 530, p. 178. Oxford, UK: Clarendon Press. ISBN 0-486-60637-6.
* Tankersley and Mosca: ''Introducing Faraday’s law''.