# Lab5 - Laboratory work 5 STUDY OF DIRECT CURRENT LAWS...

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Laboratory work №5 STUDY OF DIRECT CURRENT LAWS Objective: The acquisition of the experimental skill of dealing with direct currents in electrical circuits Tasks: Study of the Ohm’s law Study of the functional dependence of the net power of the direct electrical current from the active resistance in the circuits. 1.Experimental technique Task №1. Study of the Ohm’s law In the closed electrical circuit, beside the positive charge carriers which are are moving along the electric force field (along to the direction of electrical potential decrease),there are some number of positive charge carriers which are moving in the opposite direction(opposite direction to ) that is in the direction of the potential increase. Such kind of motion is possible only due to the influence of some forces, which are called , electromotive forces. The work done by these electromotive forces is called (emf) The part of circuit ,where the electromotive forces are acting, is known as notuniform part of the electrical circuit. Work A 12 ,done by the electrostatic(coulomb) and extraneous forces on the path1-2 spent to transfer the charge q, is equal to the following: (1) The magnitude, numerically equal to the work of the electrostatic and extraneous forces spent on the charge transfer of one unit of the positive charge, is called voltage drop or simply voltage U 12 on the path 1-2 of the circuit. According to (1) (2) From (2) we conclude that ,voltage is equal to the difference of the electrical potential only on the path, where the extraneous forces are not existing, and therefore: (3) The voltage U 12 might be expressed as a product of the electrical current and resistance (R+r) of the circuit, that is:

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(4) Where r-internal resistance of the current source. If we shall equalize equations (4) and (3) and solve them defining the current, we shall obtain the generalized Ohm’s law for non uniform part of the circuit: (5) Task №2 Study of the net power( useful output) dependence from resistance.
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