LAD4

PHYSICS № 4 Laboratory

STUDY OF DIRECT CURRENT LAWS

Group: CSSE-143K

Made by: Sain Beknazar

Instructor: Zvyaginceva Olga Alekseevna

STUDY OF DIRECT CURRENT LAWS

AIM OF THE WORK:

Experimental investigation of the generalized Ohm's law for non-uniform part of the

circuit of the direct current.

TASKS:

To study of the Ohm’s law;

To determine the EMF and the total resistance of the circuit according to

experimental data.

EXPERIMENTS DESCRIPTION

Generalized Ohm’s law should be studied on the following experimental set.

The non uniform electrical circuit on the part 1-2, which consist of the current

source with internal resistance r and external constant resistance . To identify

the depend ence of the potential difference on the path 1-2 from the value

of electrical current (see figure 3).

Figure 3 - Experimental set for study the generalized Ohm’s law

Here the following: PV is voltmeter, included to the investigated part of the

circuit in parallel way of connection, R2 is external resistance with respect to the

path 1-2, where it is possible to measure the value of the electric current; PA-ammeter

for the electric current measurement on the part 1-2. R is potentiometer,

used to alter the voltage from the second current source ɛ₁, which emf is more than ɛ₂.

In the case when the key K is (disjoint) open-ended and the wiper D of the

rheostat is located on the upper point D2, the electric current will flow on the path D₂ɛ₁R₁M, and at the same time the direction of the current (from point 1 to the point 2) and its value determined by the action of the first current source. As it might be concluded from the scheme in this case the φ₂>φ₁ always.

From the Ohm’s law we may come to the conclusion that on the path 1-2 we

have:

At the constant values ɛ₁, R₁and r this dependence has linear character. The

functional graph presents the straight line, crossing the y axis

(φ₂-φ₁)in the point I=0, φ₂-φ₁=ɛ1 (figure 4). The incline angel to the axis of

abscissa (current axis) is the obtuse one, so the coefficient before I is negative and

depends on the value of external resistance R. As it comes from (14) the increment of the potential difference connected with the current increment in the following way:

,

Figure 4 – The functional graph

The second scheme, used in the task, corresponds to the closed position of the key K and to the displacement of the wiper D in to the intermediate position of the potentiometer. The current I on the path 1-2 at this case is defined only by the current source ɛ₁, but also by the value of ɛ₂ the contribution of which is ruled by the wiper position. That is why you may fix such a value of ɛ₂ the electric current when the difference of the potentials will be greater then current source ɛ₁, i.e. φ₂-φ₁<0. The dependence of the φ₂-φ₁=f(I)in this case enables it to cross

the current axis, falling to the region of the negative values.

Procedure:

1. Compile the scheme according to figure 3, turning in the investigation part of

the circuit 1-2 the course of current with unknown EMF and resistance R1.

2. Changing the resistance R2 from 0 to 6080 Ohm through every 10 Ohm get

the dependence of the potential difference from the current. The obtained

results put into the table 1.

3. Make the graph of the dependence φ₂-φ₁=f(I). Extrapolating the graph

till the crossing with the x axis, find the EMF of the course ɛ₁ . Along the slope

find the resistance R1 (15).

4. Change the resistance R1 on the other R1’. Key K is closed.

5. At the turned off the resistance (R2=0) make by the cursor of the potentiometer

the recommended value of the current, than make the maximum value of R2.

6. Get the dependence φ₂-φ₁=f(I), decreasing R2 through every 20 Ohm. At

the approximation of the indications of the voltmeter to zero, switch their poles

and continue the measurements till R2 becomes equal to zero. The obtained

results put into the table 1.

7. Make the graph of the dependence φ₂-φ₁=f(I)on the same graph where is

the dependence f₁(I) . Determine ɛ₁ and R1 as in item 3.

8. The results of the work should be presented as a table 1 and graph.

9. Make the analysis the of the obtained results, conclusion about the role of the

course ɛ₂ and the position of the wiper D of the potentiometer.

Table 1

	Ω, { Ohm}	I,{ mA}	U,{V}	<U>	ΔU	ΔU2
R1	10	34,998	0,363	0,97	0,607	0,368
	20	31,198	0,639		0,331	0,109
	30	28,009	0,849		0,121	0,014
	40	25,499	1,012		-0,042	0,001
	50	23,498	1,164		-0,194	0,037
	60	22,006	1,295		-0,325	0,105
	80	18,497	1,47		-0,5	0,25

	Ω, {Ohm}	I, {mA}	U {V}	<U>	ΔU	ΔU2
R1’	180	19,987	0,755	0,291	-0,464	0,215
	140	22,008	0,591		-0,3	0,009
	120	23,013	0,504		-0,213	0,045
	100	23,993	0,373		-0,082	0,006
	80	25,498	0,243		0,048	0,002
	60	26,994	0,109		0,182	0,034
	40	28,489	- 0,037		0,328	0,107
	20	30,009	-0,21		0,501	0,251

Table 2

12 EMF

№	R	I, mA	U, B	N	<N>	ΔN	ΔN2
1	100	41,996	4	167	156,43	-12,082	145,976
2	200	32,221	6,19	199,54		-43,113	1858,730
3	300	25,998	7,296	191		-33,566	1126,686
4	400	21,985	8,008	175,754		10,686	114,191
5	500	18,988	8,213	155,428		1,0125	1,0251
6	600	15,997	8,497	136,064		20,376	415,172
7	700	14,490	9,202	133,217		23,223	539,321
8	800	13,507	9,599	129,476		26,963	727,043
9	900	11,991	9,990	119,94		36,5	1332,257

Calculation of the relative error:

Sn = = =27,973

N=156,43 × ± 0,27

24 EMF

№	R	I, A	U, B	N	<N>		ΔN2
1	100	80,011	7,6	608,3	575,242	-33,141	1098,344
2	200	59,997	11,485	690,27		-115,0425	13234,778
3	300	48,009	13,993	671,46		-96,211	9258,0159
4	400	40,007	15,486	619,54		-44,3	1962,924
5	500	36,005	17,008	612,34		-37,11	1377,338
6	600	30,994	17,993	557,67		17,56	308,65
7	700	28,014	18,488	517,9		57,33	3287,77
8	800	24,995	18,998	474,6		100,463	10092,9105
9	900	21,993	19,316	424,79		150,448	22634,812

Calculation of the relative error.

Sn = = = = 2,81

N = 575,24 × ± 0,89

Conclusion