Combination circuit with Series & Parallel light bulbs

• Engineering
• dss975599
In summary, the problem involves one 18 watt lamp and two 60-watt light bulbs connected in parallel and in series with a 120V circuit. The solution provided is I1 = 0.15A and I2 = 0.5A, with R1= 800 ohm and R2 = 240 ohm. However, this solution is incorrect as it does not take into account the actual current in the circuit. The correct approach is to use the rated current to calculate the resistance and then use Ohm's law to find the actual current.

Homework Statement

One 18 watt lamp and two 60-watt light bulb are plugged into a 120V circuit. For either DC or AC, the two bulbs are connected each other in parallel and in series with the lamp in the same circuit. Calculate;
i. the current flow through each light
ii. the total resistance of the circuit,

The soultion provided is I1 = P /V = 18 /120 = 0.15A ,
I2 = P / V = 60/120 = 0.5A

The Attempt at a Solution

I have tried to sketch the diagram as attached .

R1= 120/ 0.15 = 800 ohm , R2 = 120/0.5 = 240 ohm
I doubt the ans is correct . When i check thru the working again , i found that the V total = 0.15(800) + 0.5(240) = 240V ...

So , i think it's wrong ...

Correct me if i am wrong

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Your sketch is wrong. See this one:

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dss975599 and Tom.G
Your sketch is wrong. See this one:
View attachment 227053
R1= 120/ 0.15 = 800 ohm , R2 = 120/0.5 = 240 ohm
I doubt the ans is correct . When i check thru the working again , i found that the V total = 0.15(800) + 0.5(240) = 240V ...

So , i think it's wrong ...

Correct me if i am wrong

You confuse the rated current with the actual current. 0.15 A and 0.5 A are RATED bulb currents. The rated current helps you to calculate the resistance. The rated resistance REMAINS the same in any circuit but the actual current is different and it depends on the total circuit resistance.

1. How do series and parallel light bulbs affect each other in a combination circuit?

In a combination circuit with series and parallel light bulbs, the light bulbs affect each other in terms of the overall brightness of the circuit. In a series circuit, the brightness of each bulb decreases as more bulbs are added because the total resistance increases. In a parallel circuit, the brightness of each bulb remains the same regardless of how many bulbs are added because the voltage across each bulb remains constant.

2. What is the difference between a series and parallel circuit?

In a series circuit, all components are connected in a single loop, meaning the current flows through each component in succession. In a parallel circuit, the components are connected in branches, meaning the current splits and flows through each component simultaneously.

3. How does the total resistance in a combination circuit with series and parallel light bulbs change?

The total resistance in a combination circuit with series and parallel light bulbs changes depending on the arrangement of the bulbs. In a series circuit, the total resistance increases as more bulbs are added because each bulb adds to the overall resistance. In a parallel circuit, the total resistance decreases as more bulbs are added because the total resistance is divided between the branches.

4. Can a combination circuit with series and parallel light bulbs have different voltages?

Yes, a combination circuit with series and parallel light bulbs can have different voltages. In a series circuit, the total voltage is divided between the bulbs, so each bulb will have a lower voltage than the total. In a parallel circuit, each bulb will have the same voltage as the source.

5. How does the brightness of each light bulb change when more bulbs are added in a combination circuit with series and parallel light bulbs?

In a series circuit, the brightness of each light bulb decreases as more bulbs are added because the total voltage is divided among the bulbs, resulting in a lower voltage for each bulb. In a parallel circuit, the brightness of each bulb remains the same regardless of how many bulbs are added because the voltage across each bulb remains constant.