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## Homework Statement

You wish to use an LED (D

_{1}) which provides essentially zero resistance and is rated to accept either a maximum of 75 mW of power or 30 mA of current. In the following two circuits, what range values for resistor R

_{1}will be acceptable in each case if the voltage provided by V

_{1}is 12 V?

## Homework Equations

R = V / I

V = P / I

## The Attempt at a Solution

R

_{max}= V / I = 12 V / 30 mA = 400 Ω.

V

_{2}= P / I = 75 mW / 30 mA = 2.5 mV

So I need a resistor that will reduce the voltage from 12 V to 2.5 mV, requiring a voltage drop of 11.9975 V:

R

_{min}= V / I = 11.9975 V / 30 mA = 399.916667 Ω

Rounding to one or two significant figures (as mentioned in the instructions) would remove any sort of "range" from my answer. Furthermore, a 400V resistor would leave no energy for the LED. Is the problem in my answer or the large voltage supply?

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