Topic practiceQ1Moderate
This question uses a figure from the original paper. The figure is being added; the answer and explanation are already verified.
The current through an element is shown in Fig. Q1. Determine the total charge that passed through the element from t = 0 s to t = 3 s.
View answer & solution
Correct answer: C. 22.5 C
Quick explanation
Current is the rate of flow of charge, so the required charge is the signed area under the current–time graph from 0 to 3 s. The interval contains a 10 A rectangle, a 10→5 A trapezoid and a 5 A rectangle; their areas give 22.5 C.
i(t) = dq/dt ⇒ dq = i(t)dt
q = ∫03 i(t)dt
q = 10(1) + [(10 + 5)/2](1) + 5(1)
q = 10 + 7.5 + 5 = 22.5 C
1 A·s = 1 C
q1 = 10 × 1 = 10 C
q2 = [(10 + 5)/2] × 1 = 7.5 C
q3 = 5 × 1 = 5 C
q = q1 + q2 + q3
q = 10 + 7.5 + 5 = 22.5 C