Let an electric current of 1.5 A flow through an incandescent lamp in a circuit. What is the amount of charge that flows through it in 10 ms?
- A.0.015 C
- B.0.15 C
- C.1.5 C
- D.15 C
Correct answer
Explanation
The correct answer is A, 0.015 C. Charge equals current multiplied by time, so Q = 1.5 A × 0.010 s = 0.015 C.
Electric current is the rate at which charge flows, I = Q/t, so the charge that passes in a given time is Q = I × t. One ampere means one coulomb of charge passing a point every second. The trap in this question is the unit of time: 10 ms means 10 milliseconds, and one millisecond is one-thousandth of a second, so 10 ms is 0.01 s. Multiplying 1.5 by 0.01 gives 0.015 coulomb. Converting every quantity to SI units first, amperes and seconds here, avoids most mistakes of this kind.
Option B is wrong because 0.15 C would need 0.1 s, that is 100 ms. Option C is wrong because 1.5 C is the charge in a full second. Option D is wrong because 15 C would need 10 whole seconds, which comes from reading ms as seconds.
Exam tip: Q = I × t; 1 ms = 0.001 s; 1 A = 1 C per second.
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