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PRACTICE · MEMBERSIntermediate · Single correct

PRACTICE / LEDs, photodiodes and solar cells

Choose a current-limiting resistor

An LED is modeled as a constant 2.0 V forward drop. It is connected to a 9.0 V DC source and should carry 20 mA.

Find the required series resistance.

Organize the givens & assumptions
  • Vs = 9 V
  • VLED = 2 V
  • I = 0.020 A

DC steady state; ideal wires and a fixed 2.0 V forward LED drop at the target current.

  1. A0.35 Ω0.35\ \Omega
  2. B350 Ω350\ \Omega
  3. C450 Ω450\ \Omega
  4. D100 Ω100\ \Omega

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