Parallel Circuit
- Connect the bulbs together with the wire as shown in the diagram below
- Using the multimeter measure the resistance of each bulb.
- Connect the bulbs to the power supply as shown in the diagram below and switch the power on.
- Measure the voltage of the bulbs by using the multimeter and connecting the red cable to red and black cable to black
Series-Parallel Circuit
-
Connect 2 bulbs together as show in the diagram below.
- Measure the voltage and resistance of each bulb.
- Measure the current in the circuit
Results
Series Resistance
Measurement Using Multimeter
Calculating the Current of Bulb 1 and bulb 2
Using Ohm’s Law, given V = I x R,
I =
Equivalent Resistance of Parallel Circuit using two Bulbs:
Req =
Req =
Req = 1.32 Ω
Series –Parallel Resistance
Measurement Using Multimeter
Using Ohm’s Law to Calculate current
Total Current Flowing in Circuit = 1.48 + 1.52 + 2.18
= 5.18amps
Current in Circuit = 0.370amps
Equivalent Resistance of Series-Parallel Circuit using three Bulbs:
Req = (R1 + R2)+(
Req = (3.90+3.80)+ (
Req = 0.558 Ω
∴ Total Current Flowing in Series-Parallel Circuit
∴ I =
∴ I = 0.556amps
Discussion
Different circuits were used to explore how current flows. In the first test, the series circuit was used. It was found from using the multimeter that bulb 1 has a resistance of 3.90 Ω, whereas bulb 2 has a resistance of 3.80 Ω. This measurement is considered acceptable since both of the bulbs have the same properties and is identical to each other; they are to have similar resistance.
However, the voltage of the bulbs was also measured when a power supply was given. 4 x AA batteries were used as the power supply. When the voltage of the power supply was measured, the multimeter reads 6.12V. This is slightly higher than the voltage expected, since the AA batteries were 6.00V, however there were possible errors involved, such as the difficulty of determining the correct figure displayed on the multimeter since there were continuous fluctuations. This lessens the chance of recording an accurate value.
When the voltage of the bulbs was record, the voltage of bulb 1 reads 3.00V and voltage of bulb 2 reads 2.95V. This is technically half the voltage of the power supply, hence the total voltages of the 2 bulbs is 5.95V, which is approximately 6.00V, the same as the actual volts of the 4 x AA batteries.
It is believed that the reason why bulb 1 and 2 has voltages that are half of the actually 4 x AA batteries voltage is due to the fact they are in a series circuit. In a series circuit each of the resistors (bulb) shares voltage, hence as there are 2 resistors, half of the voltage goes towards one resistors and the other half goes towards the other. This theory is also stated in the kirchhoff’s voltage law, where he stated that ‘the sum of all the voltage drops around a single closed path in a circuit is equal to the total source voltage in that closed path’ (Young 2011).
Nevertheless, the amps were calculated for each bulbs given bulb one 0.769amps and bulb two 0.776amps. Since the bulbs are identical to each other, the amps they produced were similar to one another. The current in the series circuit was also measured using the multimeter, which gave a reading of 0.159amps. There is a significant difference between the measured current and the calculated current of the 2 bulbs. By theory the calculated value and measured value should be similar as the current in the series is the same for all elements in the series. It is believed there could be some errors involved when measuring the resistance of the bulbs.
In parallel circuit, the multimeter was used to determine the reading of the resistance of bulb 1 and bulb 2. It was found that bulb one is 2.70 Ω and bulb 2 is 2.60 Ω. Again they both have similar resistance, but due to their identical bulb properties. The total resistance of the bulb was also calculated to be 1.32 Ω. Since the circuit is a parallel, each of the bulbs receives a voltage of 5.62V and 5.59V. This is close to the actual voltage of the power supply. Since the voltages in parallel are not shared, each bulb is expected to receive a voltage close to 6.00V. There were some errors involved when recording the voltage and one error was the dropping of voltage from the battery. Batteries often lose their charge over time when being used, hence this causes the multimeter readings to fluctuate and the reading of the voltage for each bulbs to be lower than expected.
The last circuit that was conducted was a mix between series and parallel circuit. It was determined that the bulb connected by the series circuits shined less brighter than the bulb connected by the parallel circuit. Hence, the bulb in the parallel circuit produces a higher voltage, closer to the batteries’ voltage of 6.00V.
The amperes calculated for the bulb in the parallel circuit at 2.18amps is also higher than the bulb in the series circuit at 1.48amps and 1.52amps. The total equivalent resistance was also calculated to be 0.558 Ω. This gives rise to the total current flowing in the series-parallel resistance of 0.556amps. This ampere is close to the value of the total current flowing in the circuit of 0.370amps. Theoretically they are to be more similar however it is believed there could be some errors involved with the measurement.
This practical had many errors involved such as the fluctuation of the multimeter. A possible improvement to the practical is to reduce the fluctuation on the reading of the multimeter. Since the charge of the batteries drops over time, this causes the multimeter to fluctuate. It is more preferably to use a battery back such as a transformer, as this would lessens the chance of charges dropping, hence less fluctuation of the multimeter reading.
Conclusion
From following the method, it was found that when a series-circuit is used the bulbs share the voltage from the power supply, however when a parallel circuit was used, the bulb receives nearly full voltage from the power supply. It was also observed that the bulb shines brighter in the parallel circuits, which also gives indication that more voltage is flowing to the bulb. Nevertheless there were errors involved during the practical, which caused some calculated, and measurement values to have a less level of accuracy. An improvement was suggested which would increase the possibility of observing a more accurate data.
Reference
Young, HD 2011, College Physics, 9th edn, Addison-Wesley, Boston, US
Millikan, RA 2000, Elements of Electricity, American Technical Publisher, Orland Park, US
