Electronics > Beginners

Elektor, Quiz problem

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MikeK:
In the Electronics for Starters (4) column in the April 2012 issue there is a quiz.  But I think there is a mistake for question 1.  I can't get even close to the desired current of 350mA with any of the resistor values.  Are the answers missing a decimal place?

IanB:
Can you post a summary of the question?

MikeK:
I apologize if this is a copyright violation...

mikeselectricstuff:
Yes - they missed a DP - should be 0.47 ohms for 350mA

IanB:
Yes, the question has an error in it.

If each LED drops 3.4 V that would make 10.2 V. If you then pass 350 mA through a 22 ohm resistor you would add on 7.7 V giving a total of 17.9 V. That is higher than the battery voltage.

I guess the resistor choices should be 2.2 ohms, 4.7 ohms or 10.0 ohms. (Or not. Maybe Mike knows best...)

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