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Combination circuit with Series & Parallel light bulbs

  • Engineering
  • Thread starter dss975599
  • Start date
  • #1
31
1

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


Homework Equations




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

Last edited by a moderator:

Answers and Replies

  • #3
427
119
Your sketch is wrong. See this one:
upload_2018-6-17_12-32-35.png
 

Attachments

  • #4
31
1
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
 
  • #5
427
119
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.
 

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