# physics lab report group four project

Data Collection

Table (1): the voltage between the plates and current flowing through the circuit as the distance between the plates (placed in the 1:1 mountain soil to water suspension) was varied.

Trial

Voltage

(V)

(V)

(±0.2V)

Current

(I)

(mA)

(±0.01mA)

Distance between plates

(l)

(cm)

(±0.5cm)

Length of plates

(L)

(cm)

(±0.1cm)

Width of plates

(W)

(cm)

(±0.1cm)

5.0

0.04

7.0

5.5

3.5

2

5.0

0.07

4.0

5.5

3.5

3

4.2

0.15

.0

5.5

3.5

Table (2): the voltage between the plates and current flowing through the circuit as the distance between the plates (placed in the 1:1 garden soil to water suspension) was varied.

Trial

Voltage

(V)

(V)

(±0.2V)

Current

(I)

(mA)

(±0.01mA)

Distance between plates

(l)

(cm)

(±0.5cm)

Length of plates

(L)

(cm)

(±0.1cm)

Width of plates

(W)

(cm)

(±0.1cm)

5.0

0.05

6.5

4.0

3.5

2

4.4

0.11

2.5

4.0

3.5

3

3.8

0.17

.0

4.0

3.5

Data Processing and Presentation

. Conversion of measurements to SI units

Table (3): the voltage between the plates and current flowing through the circuit as the distance between the plates (placed in the mountain soil suspension) was varied.

Trial

Voltage

(V)

(V)

(±0.2V)

Current

(I)

(A)

(±0.00001A)

Distance between plates

(l)

(m)

(±0.005m)

Length of plates

(L)

(m)

(±0.001cm)

Width of plates

(W)

(m)

(±0.1m)

5.0

0.00004

0.070

0.055

0.035

2

5.0

0.00007

0.040

0.055

0.035

3

4.2

0.00015

0.010

0.055

0.035

Table (4): the voltage between the plates and current flowing through the circuit as the ...

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Trial

Voltage

(V)

(V)

(±0.2V)

Current

(I)

(A)

(±0.00001A)

Distance between plates

(l)

(m)

(±0.005m)

Length of plates

(L)

(m)

(±0.001cm)

Width of plates

(W)

(m)

(±0.1m)

5.0

0.00004

0.070

0.055

0.035

2

5.0

0.00007

0.040

0.055

0.035

3

4.2

0.00015

0.010

0.055

0.035

Table (4): the voltage between the plates and current flowing through the circuit as the distance between the plates (placed in the garden soil suspension) was varied.

Trial

Voltage

(V)

(V)

(±0.2V)

Current

(I)

(A)

(±0.00001A)

Distance between plates

(l)

(m)

(±0.005m)

Length of plates

(L)

(m)

(±0.001m)

Width of plates

(W)

(m)

(±0.001m)

5.0

0.00005

0.065

0.040

0.035

2

4.4

0.00011

0.025

0.040

0.035

3

3.8

0.00017

0.010

0.040

0.035

2. Cross sectional area of soil + water suspension through which current is flowing

a. Mountain soil

b. Garden Soil

3. Conductivity of the soil samples

For a substance at constant temperature:

Where R is the resistance of the substance, ? its resistivity, l its length, and A its cross-sectional area.

Assuming the substance is ohmic, its resistance R will be given by the equation , where V is the potential difference across the substance and I the current flowing through it.

By substituting for R in equation (1.1), we get that:

(1.2)

If both sides of equation (1.2) are multiplied by , then:

(1.3)

Since conductivity (?) is equal to the reciprocal of resistivity: i.e. , the conductivity of a substance is given by the following equation:

(1.4)

a. Mountain Soil

Trial one

Substitute 15.0 V for V, 0.00004 A for I, 0.070 m for l, and 0.0019 m2 for A:

Trial two

Substitute 15.0 V for V, 0.00007 A for I, 0.040 m for l, and 0.0019 m2 for A:

Trial three

Substitute 14.2 V for V, 0.00015 A for I, 0.010 m for l, and 0.0019 m2 for A:

b. Garden Soil

Trial one

Substitute 15.0 V for V, 0.00005 A for I, 0.065 m for l, and 0.0014 m2 for A:

Trial two

Substitute 14.4 V for V, 0.00011 A for I, 0.025 m for l, and 0.0014 m2 for A:

Trial three

Substitute 13.8 V for V, 0.00017 A for I, 0.010 m for l, and 0.0014 m2 for A:

Conclusion and Evaluation

In this practical, the electrical conductivity of two soil samples was determined. As we hypothesized, the electrical conductivity of the sample of garden soil was found to be greater than that of mountain soil: the average electrical conductivity of the garden soil suspension was found to be 12.6*10-5 AV-1m-1, whereas that of the mountain soil suspension was found to be 8.4*10-5 AV-1m-1.

Sources of Error

. The ammeter used is not 'perfect': it has some resistance. This will cause the experimental resistance of the resistors to be greater than the actual resistance because we assumed that all the resistance in the circuit was due to the soil suspension.

2. The wires have resistance. This will also cause the experimental resistance of the soil suspension to be greater than the actual resistance because we assumed that all the resistance in the circuit was due to the soil suspension.

3. The uncertainty of the ammeter may have caused errors in current measurements.

4. The uncertainty in the voltmeter may have caused errors in potential difference measurements.

5. The temperature of the suspension may have increased during the experiment. As a result, its resistance will also increase since the resistance directly proportional to the temperature of the substance.

6. Approximation when measuring the dimensions of the copper plates: there was an uncertainty of ±0.1cm in length and width measurements. This may have caused error in the final results of the experiment.

7. Approximation when measuring the distance between the copper plates: there was an uncertainty of ±0.5cm in distance measurements. This may have caused error in the final results of the experiment.

8. The

Improvements

. Using an ammeter with lower resistance to minimize the contribution of the ammeter to the total resistance in the circuit.

2. Using a more accurate voltmeter to minimize errors in potential difference measurements.

3. Using a more accurate ammeter to minimize errors in current measurements.

4. Using wires with lower resistance to reduce the contribution of the wires to the total resistance in the circuit.