alleryStart learning →An indicator light on a DVD player has a resistance of 140 ohms and passes 25.0 mA. What voltage supplies it?
A5.60 V
B0.35 V
C56.0 V
D3.50 V
Answer & Solution
Correct answer: D. 3.50 V
1. The voltage across a resistance is V = IR.
2. Convert the current to amperes: 25.0 mA = 0.0250 A.
3. Multiply: V = 0.0250 A x 140 ohms.
4. This gives V = 3.50 V.
5. 3.50 V is a sensible indicator-lamp voltage, while 56.0 V comes from leaving the current in milliamperes but shifting the decimal point only one place.
_Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section 20.2 Ohm's Law: Resistance and Simple Circuits_
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