Objectives:
After performing this activity, you should be able to:
1. connect loads in different ways and
2. explain the similarities and differences between the circuit connections.
Materials Needed:
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Procedure:
1. Construct a circuit using three connecting wires, two identical bulbs and two batteries such that when one bulb is unscrewed the other bulb goes out also.
Once you’re done with the task, disconnect the battery from the circuit.
2. Draw your setup. Label this Circuit A.
3. Trace the paths of current in Circuit A.
Q13. How many path/s of current are there in the circuit?
Q14. Why did the other bulb go out also when you unscrewed the other?
4. This time, construct a circuit using four connecting wires, two identical bulbs and two batteries such that when one bulb is unscrewed, the other bulb remains lighted. Once you’re done with the task, disconnect the battery from the circuit.
5. Draw your setup. Label this Circuit B.
6. Trace the path of current in Circuit B.
Q15. How many paths can the current take in Circuit B?
Q16. Explain why the other bulb remains lighted when you unscrewed one of them.
7. Put Circuits A and B side by side. Observe the brightness of the bulbs.
Q17. Which circuit has brighter bulbs, A or B?
Q18. Based on the brightness of the bulbs, compare the current in Circuit A and in Circuit B?
8. Measure the voltage across the two bulbs as well as the voltage across each bulb in Circuit A. Record your readings in Table 3. Do the same in Circuit B.
Table 3
Circuit Voltage drop (V) Voltage across the two bulbs (V)
Bulb 1 Bulb 2 A
B
In Circuit A, the bulbs are connected in series, while in Circuit B, the bulbs are connected in parallel. Series and parallel connections are the two ways of wiring loads. In a series connection, there is only one path for the current. In a parallel connection the current from the battery can branch out to the two bulbs. Hence the current can take the path through Bulb 1 and the path through Bulb 2.
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The current in Circuit A takes only one path, passing through the two bulbs.
When one bulb is unscrewed or removed, a gap is created. A gap or a break anywhere in the path stops the flow of charges and therefore no current passes through to the other bulb.
In Circuit B, the current can take two paths - one path for each bulb. When one bulb is unscrewed or removed, the other bulb is still part of a complete circuit and remains lighted.
Let us compare the other characteristics of Circuits A and B. Circuit A is similar to the circuit of three bulbs you made in Activity 2. The bulbs are connected in series. In this type of connection, the resistance increases with the number of bulbs added in the circuit. The total resistance in the circuit is the sum of the resistance offered by each bulb.
You observed in Activity 2 that as the total resistance increases, the current through the circuit decreases. You also measured the current and voltage at different parts of the circuit. Your measurements showed that the current is the same anywhere in a series circuit, and the sum of the voltages across each bulb equaled that of the voltage source.
On the other hand, Circuit B has 2 bulbs which are connected in parallel.
You observed that the voltage across each bulb is almost equal to the voltage of the two dry cells, indicating that the voltage anywhere in the circuit is the same.
However, when the brightness of the bulbs in Circuit B is compared to that of the bulbs in Circuit A, those of Circuit B were brighter than those of A. This means the current in B is greater than the current in A. Since the voltage in A and B are the same (2 dry cells), the greater current in B indicates that the total resistance of Circuit B is less than the total resistance of Circuit A. We can infer that when loads (bulbs) are connected in parallel, the total resistance of the circuit decreases; when the loads are connected in series, the total resistance increases. Table 4 compares the total current, total voltage and total resistance of series and parallel circuits.
Table 4
Series connection Parallel connection Total current Same as current in individual load Equal to the sum of current in
individual loads Total voltage Equal to the sum of the voltages
across each load
Same anywhere across two points in the circuit
Total resistance
Increases with increasing load Decreases with increasing load
Look at the connections of wirings in your house. Which are connected in series? Which are connected in parallel? What are the advantages and disadvantages of each type of connection?
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Safety in Using Electricity
Your parents have probably cautioned you about the use of electrical devices even before you reached school age. You were told not to touch electrical outlets or insert anything into it. You were told not to touch any electrical wires in the house.
Well they may not have explained it to you back then, but they have valid reasons.
Firemen advise homeowners to check the electrical connections in their homes especially the condition of the wires. They advise homeowners to replace exposed electrical wires. Why is there a need to cover exposed wires? You will find the answer in Activity 4.