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{\displaystyle j=|{\vec {j}}|={\frac {I}{S}},}

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{\displaystyle I=|\int \limits _{S}({\vec {j}},{\vec {dS}})|=|\int \limits _{S}j_{n}dS|},

{\displaystyle j_{n}} () {\displaystyle dS}; {\displaystyle {\vec {dS}}} , , , .

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, ( ) {\displaystyle {\vec {v}}} {\displaystyle q}( ; ), {\displaystyle n},

{\displaystyle {\vec {j}}=nq{\vec {v}}}

{\displaystyle {\vec {j}}=\rho {\vec {v}},} {\displaystyle \rho } {\displaystyle {\vec {j}}} {\displaystyle {\vec {v}}}, , , q .

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{\displaystyle {\vec {j}}=\sum _{i}n_{i}q_{i}{\vec {v}}_{i},} ; {\displaystyle n_{i}\,\!} , {\displaystyle q_{i}\,\!} , {\displaystyle {\vec {v}}_{i}} .

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{\displaystyle {\vec {j}}=\sum _{i}q_{i}{\vec {v}}_{i}} , , i , , , , .

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( ) . :

{\displaystyle {\vec {J}}=\sigma \,{\vec {E}},}

{\displaystyle \sigma } ,

{\displaystyle {\vec {J}}} ,

{\displaystyle {\vec {E}}} .

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{\displaystyle J_{i}=\sum \limits _{k=1}^{3}\sigma _{ik}\,E_{k},} .

( , ) . . , {\displaystyle \sigma _{ik}} , , {\displaystyle \sigma _{ik}} : {\displaystyle \sigma _{11}}, {\displaystyle \sigma _{22}} {\displaystyle \sigma _{33}}. , {\displaystyle \sigma _{ii}} {\displaystyle \sigma _{i}},

{\displaystyle J_{i}=\sigma _{i}E_{i}.} {\displaystyle \sigma _{i}} . [3].

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, , ( , ), [4] , E. , E, , , , , , . J E {\displaystyle \sigma =dJ/dE} ( : {\displaystyle \sigma _{ik}=dJ_{i}/dE_{k}}).

G L S , , :

{\displaystyle G=\sigma {\frac {S}{L}}.}

(/) −1−1. (−1).

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( R r) , , ;

{\displaystyle R={\frac {U}{I}},}

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ρt=ρ0(1+αt), ρt=ρ0(1+αt),

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{\displaystyle U={\mathcal {E}}={\text{const}}}. {\displaystyle R}:

{\displaystyle I={\frac {U}{R}}.}

. ( ) , {\displaystyle R\rightarrow 0} , .

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, {\displaystyle r}. , . {\displaystyle {\mathcal {E}}} {\displaystyle r}.

3 ( ) ( ).

{\displaystyle {\mathcal {E}}=U_{r}+U_{R},}

{\displaystyle U_{r}=I\cdot r,} ;

{\displaystyle U_{R}=I\cdot R,} .

{\displaystyle R=0} . {\displaystyle I_{\text{s.c.}}} . {\displaystyle U_{\text{xx}}} , :

{\displaystyle r={\frac {U_{\text{xx}}}{I_{\text{s.c.}}}}.}

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I = E / (R + R), (4)

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I = E / (R + R). (5)

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I = I - I. (6)

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