Determine the resistance of Rl

  • Thread starter TyErd
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  • #1
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Homework Statement


All LEDs in the following circuit are identical. Each LED has a switch on voltage of 2V and draws a current of 20mA for optimal light production.

Determine the resistance of Rl that gives optimum operation for all LEDs.


Homework Equations


Ohms Law V=IR


The Attempt at a Solution


becuase the LEDs are connected in parallel I calculated the voltage for Rl to be 9-2 =7V then divided that by 20mA which gave me 350ohms, which is incorrect.
 

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Answers and Replies

  • #2
rl.bhat
Homework Helper
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Each LED draws 20 mA current. There are three LEDs. So the total current drawn from the battery is........?
 
  • #3
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OMG im an idiot, I didn't read the question properly, I thought the 20mA was divided amongst the 3 LEDs. Haha, anyway Thankyou!
 

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