DC Circuit - this is a lab report PDF

Preview

Summary

this is a lab report...

Description

DIPLOMA IN SCIENCE PHY150: ELECTRICITY & MAGNETISM

LABORATORY REPORT NO EXPERIMENT : 3 TITLE : DC CIRCUIT GROUP : AS1203H GROUP MEMBERS : STUDENT’S NAME

STUDENT ID

OBJECTIVES 1. To measure the current and voltage for a simple DC circuit. 2. To study series connection of resistors. 3. To study parallel connection of resistor

THEORY For a certain piece of material with fixed resistance. Ohm’s law state that the potential difference (voltage) between the two ends of the material is directly proportional to the current flows through the material: V = IR

(1)

for a simple DC circuit shown in Figure (1), the resistance R = V/I. Where V is the potential difference between two points (voltage applied) measured in volts (V), R is the resistance of the element measured in ohm ( 𝜴), and I is the current flows across the element measured in Ampere (A). Combination of resistors: 1. Parallel combination of resistors: When resistors connected side by side, the combination called parallel as shown in Figure (2). The current is divided between the two resistors according to the magnitude of each resistance where I₁ = 𝐼𝑡𝑜𝑡𝑎𝑙= I₁ + I₂

𝑉 𝑅₁

and I₂ =

𝑉 . 𝑅₂

the total current flowing through the circuit is given by:

(2)

And the voltage across the whole circuit will be the same. 𝑉𝑝𝑜𝑤𝑒𝑟 𝑠𝑢𝑝𝑝𝑙𝑦 = 𝑉1 = 𝑉2

(3)

The equivalent resistance is given by: 1 1 1 = + 𝑅𝑒𝑞 𝑅₁ 𝑅₂

(4)

2. Series combination of resistors: When resistors follow each other then the elements are connected in series, see Figure (3) Where the current flows across R₁ and R₂ is the same.

𝐼𝑡𝑜𝑡𝑎𝑙= 𝐼1 = 𝐼2

(5)

While the summation of the voltage across the two resistances is equal to the voltage across the power supply. 𝑉𝑝𝑜𝑤𝑒𝑟 𝑠𝑢𝑝𝑝𝑙𝑦 = 𝑉1 + 𝑉2

(6)

The equivalent resistance for the series combination is given by: 𝑅𝑒𝑞= 𝑅1 + 𝑅2

(7)

PROCEDURE PART I: MEASURING THE CURRENT AND THE VOLTAGE IN SIMPLE DC CIRCUIT. 1. The experiment was conducted through stimulation on the link: : https://phet.colorado.edu/sims/html/circuit-construction-kit-dc-virtuallab/latest/circuitconstruction-kit-dc-virtual-lab_en.html 2. The experiment started by clicking on the battery symbol in the bottom right of the screen, and show current (conventional) was clicked, then a simple DC circuit contains of battery, resistance, switch, and wires was constructed as shown in Figure (4). 3. The voltmeter from the right second box was selected and the two terminals with end points of the resistor were connected. What is the combination between resistance and voltmeter?

4. The ammeter was dragged and connected with the circuit in the series. 5. The reading of the voltmeter, v1 in was recorded in the data analysis, table 1. 6. The reading of the Ammeter I1 was recorded on table 1. 7. The values were clicked on and the resistance R was recorded in table 1. 8. The battery was clicked on and the voltage was changed to 20 V 9. Steps 6,7, and 8 were repeated then the results v2, I2, R were recorded in table 1. 10. The voltage then was changed to 30 V and steps 6,7, and 8 were repeated and recorded in table 1. 11. The circuit was screen shotted and pasted in the report.

PART II: SERIES CONNECTION OF RESISTORS 1. Another resistor was connected in the circuit in series as shown in Figure (5)

Figure (5) 2. Then, the power supply was set to 120 Volts. And the two resistance was set to 𝑅1 = 20𝜴, 𝑅2 = 30𝜴. 3. The voltmeter was connected across the resistance 𝑅1 to measure the voltage drop 𝑉 1 . 4. The voltmeter was connected across the resistance 𝑅2 to measure the voltage drop 𝑉 2 5. The voltmeter was connected across the power supply to measure the voltage 𝑉 𝑡𝑜𝑡𝑎𝑙. 6. 𝑉1 + 𝑉2 was calculated and it was compared to the total voltage across 𝑅1 and 𝑅2 (step 5). 7. The electric current, I was measured using the Ammeter before 𝑅1 between 𝑅1 and 𝑅2 , after 𝑅2 . 8. The product of I x 𝑅1 was compared to the value of 𝑉 1 . 9. The product of I x 𝑅2 was compared to the value of 𝑉 2 . 10. All the screenshots were inserted in the lab report.

PART III: PARALLEL CONNECTION OF RESISTORS PROCEDURE 1. The circuit has been connected as shown in figure (6).

Figure (6)

2. The voltage of the power supply (battery) was adjusted to 120 volts. 3. The voltage of V1 across R1 using the voltmeter has been measured.(the copy of the circuit was taken). 4. The voltage V2 across R2 using the voltmeter has been measured.(the copy of the circuit was taken). 5. V1 and V2 have been compared to the output from the power supply Vtot (battery). 6. The current I1, through R1 using the ammeter has been measured. (the copy of the circuit was taken). 7. The current I2, through R2 using the ammeter has been measured. (the copy of the circuit was taken). 8. The total current in the circuit I (total) has been measured. (the copy of the circuit was taken). 9. I1 + I2 has been calculated and compared to result in 8. 10. All the data has been recorded in the lab report.

DATA CALCULATIONS AND RESULTS: PART I: MEASURING THE CURRENT AND THE VOLTAGE IN SIMPLE DC CIRCUIT

1. Write your results from Part I in table 1. Table 1 Trial

V (v)

I (A)

R (𝛺 )

Rcal = V/I

1

9.0

0.90

10.0

10.0

2

20.0

2.00

10.0

10.0

3

30.0

3.00

10.0

10.0

2. Comment on your results. = Potential difference is directly proportional to the current. However, the resistance does remain the same.

3. Paste your graph here.

PART II: SERIES CONNECTION OF RESISTORS 1. Table 2 𝑉1

𝑉2

𝑉𝑡𝑜𝑡𝑎𝑙

𝑉1 + 𝑉2

48.0 V

72.0 V

120.0 V

120.0 V

2. Comment on the result: The voltage of 𝑉𝑡𝑜𝑡𝑎𝑙 is same as the voltage of 𝑉 1 + 𝑉2 3. I (before 𝑅1 ) = 2.40 A , I (between 𝑅1 & 𝑅2 ) = 2.40 A , I (after 𝑅2 ) = 2.40 A Comment on the current readings: The electric current is same even if the Ammeter is put before 𝑅1 , between 𝑅1 & 𝑅2 or after 𝑅2 . 4. I x 𝑅1 = 48.0 V 5. I x 𝑅2 = 72.0 V

𝑉 1 = 48.0 V 𝑉 2 = 48.0 V

Comment on the results: The value of I x 𝑅1 and 𝑉 1 is the same. The value of I x 𝑅2 also same with 𝑉 2

6. Screenshots of:

(Voltage, 𝑉1 reading at 𝑅1 )

(Voltage,𝑉2 reading at 𝑅2 )

(Voltage, 𝑉𝑡𝑜𝑡𝑎𝑙 reading at power supply)

(Electric current, I measured before 𝑅1 )

(Electric current, I measured between 𝑅1 and 𝑅2 )

(Electric current, I measured after 𝑅2 )

PART III: PARALLEL CONNECTION OF RESISTORS 1. Screenshots of:

(voltage reading across R1)

(ammeter reading across R1)

(voltage reading across R2)

(ammeter reading across R2)

(ammeter reading for total current I total)

2.Result table 3 : V1

V2

Vtotal

120v

120v

120v

3.Comment on the result obtained: based on the result that was obtained, the results for V1, V2, and Vtotal were the same. This is because the circuit is in parallel therefore, the voltage is the same. 4.Result table 4: I1

I2

Itotal

I1 + I2

6A

10A

10A

16A

5. Comment on the result obtained: based on the results that was obtained, the ammeter reading for I1 is 6A , the ammeter reading for I2 is 10A. The reading was different, because the circuit was in parallel. Therefore. The total reading ammeter for this circuit is 16A

DISCUSSION This experiment was conducted to study more about Ohm’s Law which states that the potential difference is directly proportional to the current flows through the material (V=IR). To experiment this,a website stimulator was used which is https://phet.colorado.edu/sims/html/circuitconstruction-kit-dc-virtual-lab/latest/circuit-construction-kit-dc-virtual-lab_en.html. In this stimulator, experimenters can test their own circuit either parallel or series circuit. For experiment part I, using the stimulator, a series circuit was formed that contained a resistor, battery, ammeter and voltmeter that were being attached together by wires. The battery is being manipulated by changing the voltage from 9V to 20V and then to 30V. Based on the results and graph above, when the potential difference increases, the current also increases. However, the resistance remained the same. This proves the formula I=V/R. Alternately, if the resistance in a circuit is increasing and the voltage does not change, the current will decrease. In experiment part II, the two resistors were connected in series. The voltmeter was connected across the resistor because voltmeter cannot be connected in series because it has high resistance and current would not flow through it. The result shown that voltage at 𝑅1 is lower than the voltage at 𝑅2 . This is because the resistance of 𝑅1 is lower than resistance at 𝑅2 . High resistance means high voltage needed to make sure the current can flow through the resistor and the circuit. Next, the result also shown that the current is same whether the ammeter was connected before 𝑅1 , between 𝑅1 and 𝑅2 or even after 𝑅2 . To make it clearer to understand, the current that flow in circuit before it passes through 𝑅2 and the current that have passed through the 𝑅1 is the same. The same current that has passes through 𝑅1 will pass through 𝑅2 too. This is because there is no other path to travel but to pass through next resistance. This is how current remains the same. From the results that were obtained from part 3 experiment, when resistors were connected in parallel, each experienced the same voltage. Hence the full voltage of the battery was applied to each resistors.Vtotal=v1=v2. While the current flows in parallel circuits, the current is not the same.Therefore, the total current that leaves the battery breaks into 2 branches Itotal= I 1 + I2 .When conducting the experiment the voltage of the battery was high up to 120v, therefore, the resistance of the wires was adjusted to 20 and 30r, if not the circuit will burn. Since this is an online experiment, there are not many errors in the experiment. But the most obvious one is human error which is a personal error which is made by the person herself. The first one is wrong connecting the circuit. For example, ammeter is used to measure the current. The ammeter must be connected in series with the circuit. If it connected wrongly, the current’s reading will be wrong and it can damage the ammeter. So, make sure the ammeter must always in series with the circuit. Secondly, mistakes in reading the values that always happen because not being careful enough in taking the measurements. Therefore, to get more accurate values, repeat it for 2 or 3 times or let 2 or 3 persons read the measurement together.

QUESTION 1. What do you expect if you connect the ammeter in parallel with the resistance? = With a very low resistance in the ammeter, all of the available current will flow through the ammeter .The ammeter will short circuit the element and a large current passing through the ammeter will burn out the coil of the ammeter. And if it is not damaged, it won't give a typical reading for the circuit being tested, because the circuit has been altered. 2. What do you expect if you connect the voltmeter in series with the resistance? = Voltmeters have huge resistance because they are used to measuring the voltage and the current should not flow through it. But when the voltmeter is connected in series, the current would not flow through the circuit because of high resistance. 3. Write the benefits of connecting rheostat in electric circuits. = Rheostat is an adjustable resistor used in applications that require the adjustment of current or the varying of resistance in an electric circuit. The rheostat can adjust generator characteristics, dim lights, and start or control the speed of motors.

CONCLUSION To conclude from this experiment, direct current is a type of current which flows in one direction. The flow of direct current in a circuit can only be accomplished when the circuit is closed, but the flow of current ceases when the circuit is open. To link the components, a simple current requires a power source that supplies a certain amount of voltage as well as a wire. To open or close the circuit, a switch is used. In a Dc circuit, the voltage supply produces a potential difference that induces the flow of current. The higher the voltage, the greater the current. This relationship is outlined by the Ohm’s law....