Ohms Law - Online - PHET 1 PDF

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Ohms Law-Online-PHET 1...

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Worksheet of Ohm’s Law by using PHET Simulation ID: 20190407D

Student Name: Yanet Gloria Condori Inga

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Title of the Experiment: Ohm’s Law Objectives: 1) To study the relationship between the electric current passing through a resistance and the potential difference across it. 2) Use Ohms’ law to find the equivalent resistance of the different combinations of resistors. 3) To distinguish between the Ohmic resistor and the non‐Ohmic resistor.

Apparatus: DC ‐ Power supply, voltmeter, ammeter, resistors, and connecting wires. Theory and Background: The electric field inside a conductor equals zero when it is at electrostatic equilibrium, but when the charges move in a conductor they produce an electric current, which is defined by the current density (J). For an Ohmic material the ratio of the current density (J = I/A) and the electric field (E) is constant and equals the conductivity ( σ ). Hence Ohms’ law can be written as: J = σ E …………..………….. (1) Where J is the current density, given by: J = I / A I is the current, A is the cross sectional area of the conductor, E is the electric field and σ is the conductivity of the material, which is equal to inverse of the resistivity of the material (ρ), σ = (1/ρ) For a straight wire of cross sectional area (A = π R2; R is the radius of the wire) and length (L) and a potential difference (V) is maintained across it, E is given by the expression: E = V/ L Hence:

So that:

1

But

,

V  RI ……………….. (2)

Hence:

Resistors are one of the main components of any electric circuit, and some circuits need more than one resistor to produce a high (or low) equivalent resistance. Depending on the purpose for which the circuit is built, resistors can be connected in series or in parallel. For two resistors, R1 and R2, the series and parallel connections, and the equivalent resistance, are shown in Figures 1 (a) and 1 (b).

For resistors connected in series: Figure 1(a)

When the resistors are connected in parallel:

Figure 1(b)

Circuit Connection: The circuit that we will use is shown in Figure 2

Figure 2: Circuit Diagram

To do the experiment by using PHET interactive simulation follow the following steps: 1) Click on the following link from PHET Colorado Simulation https://phet.colorado.edu/en/simulation/circuit-construction-kit-dc

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2) 3) 4) 5)

Download Circuit Construction Kit: DC Click on Lab Choose Conventional Current Use the components in the left side to build the circuit shown below: Re (rheostat) Variable resistor

R1 = 5Ω

6) Click on the resistor (R1) and fix it at 5Ω. That is R1 = 5Ω. 7) Click on the Battery and fix it at 120V. 8) Click on the Voltmeter from the right side and drag it to measure (V1) the voltage across R1. 9) Click on the Ammeter from the right side and drag it and put it in series with R1 (before or after R1) to measure (I1). 10) Vary the rheostat ( ) to obtain 6 different readings of the electric current (I) and the corresponding values of the voltage (V). Then Record the values into table 1. 11) Replace R1 by R2=10Ω as shown below:

12) Again vary the rheostat ( ) to obtain 6 different readings of the electric current (I) and the corresponding values of the voltage (V). Then Record the values into table 1.

13) Connect R1=5Ω and R2=10Ω in series as shown below, and again vary the rheostat ( ) to obtain 6 different readings of the electric current (I) and the corresponding values of the voltage (V). Then Record the values into table 1.

R1 and R2 in Series Connection

14) Now connect R1=5Ω and R2=10Ω in parallel as shown below, and also vary the rheostat ( ) to obtain 6 different readings of the electric current (I) and the corresponding values of the voltage (V). Then Record the values into table 1.

R1 and R2in parallel connection

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Note that the Voltmeter is always connected in parallel with the element while the Ammeter in series Table (1)

R1 (5 )

Equivalent Resistance in series

R2 ( )

Equivalent Resistance in parallel

V(V) 57.14 35.29

I (A) 11.43 7.06

V(V) 77.42 54.55

I (A) 7.74 5.45

V(V) 87.80 66.67

I (A) 5.85 4.44

V(V) 45.28 26.09

I (A) 13.58 7.83

24 17.14 13.04 10.91

4.80 3.43 2.61 2.18

40 30 23.53 20

4 3 2.35 2

51.43 40 32.14 27.69

3.43 2.67 2.14 1.85

17.14 12 9.02 7.50

5.14 3.6 2.71 2.25

I (A) 14

12

y = 0.2x - 0.0001

10 8 6

4 2 0 0

10

20

30

5

40

50

60

6

1- Plot a graph V versus I for each case? 2- Does the best straight lines passes through the origin? Explain. En las gráficas se observa que si se reemplaza para intensidad igual a cero el voltaje me sale diferente de cero, esto debido a la Resistencia, y estos materiales que no cumplen con la ley de Ohm se les llama materiales no ohmicos. 3- Calculate the slope of each graph and determine the resistance (R) from the graph (slope) and experimentally? Record the results into table 2. Aproximadamente la Resistencia en cada gráfica son las siguientes: Gráfica 1: I/V = 1/R, 0.2 = 1/R, R = 5 Gráfica 2: I/V = 1/R, 0.1 = 1/R, R = 10 Gráfica 3: I/V = 1/R, 0.0666 = 1/R, R = 15.015 Gráfica 4: I/V = 1/R, 0.2999 = 1/R, R = 3.334

Table (2)

Slope

The experimental Resistance (Ω)

δ%

Graph 1

5

R1 experimentally = 5

0

Graph 2

10

R2 experimentally = 10

0

7

Graph 3

15.015

Req experimentally = 15

0.099

Graph 4

3.334

Req experimentally = 3.333

0.0299

4- What is the difference between Ohmic resistor and a Non-Ohmic resistor? Ohmic: aplica para corriente continua, la caída neta de voltaje debe ser igual a cero, en cualquier bucle.

Non-ohmic: no aplica para corriente continua, son aquellos cuya resistencia cambia, cuando la diferencia de potencial o corriente eléctrica 5- When the potential difference, V, across an ohmic resistor is increased what effect does this have on: a. The electric current (I): nuestra intensidad de corriente eléctrica es directamente proporcional con nuestra diferencia de potencial, así que si la diferencia de potencial aumenta, entonces también lo hace la intensidad de corriente.

b. The resistance (R): la Resistencia ohmica es inversamente proporcional a la intensidad de corriente, de esa manera es como esta va a interferir en nuestra diferencia de potencial. Conclusions: A partir de lo realizado en el informe se concluye que lo descrito en la La ley de Ohm se comprueba ya que este cumple con la tendencia de la línea recta y aquellos materiales no ohmicos tienen una tendencia a ser una función cuadrática. Esta también cumple con la ecuación de nuestra función lineal, ya que la pendiente nos resulta la inversa de la Resistencia, que reemplazando se obtienen los valores esperados.

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