Question 5.13: Figure 5-22b is a continuity tester. After you turn off all ...
Figure 5-22b is a continuity tester. After you turn off all the power in a circuit under test, you can use this circuit to check for the continuity of cables, connectors, and switches. How much LED current is there if the series resistance is 470 Ω?

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When the input terminals are shorted (continuity), the internal 9-V battery produces an LED current of:
I_S=\frac{9 \ V − 2 \ V}{470 \ Ω} =14.9 \ mA
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