# Combination circuit with Series & Parallel light bulbs

• Engineering

## 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

#### Attachments

• 946.png
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Your sketch is wrong. See this one:

#### Attachments

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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.