WAEC 2018 Physics · Question 47

Which of the following statements about parallel plate capacitors is/are correct? I. Capacitance of the…

Question

Which of the following statements about parallel plate capacitors is/are correct? I. Capacitance of the capacitor is inversely proportional to the distance between the plates II. Capacitors can filter a.c signals from d.c III. Capacitors can store charges

A.I only
B.I and II only
C.II and III only
D.I, II and III

Answer: D. I, II and III

Explanation written with AI and checked against the answer key

Step 1: Analyze the question We must decide which of the three statements about parallel plate capacitors are true. Step 2: Check each statement Statement I: Capacitance is inversely proportional to the distance between the plates. For a parallel plate capacitor: C = ε₀εᵣA / d Capacitance C is directly proportional to the plate area A and inversely proportional to the separation d. So Statement I is correct. Statement II: Capacitors can filter a.c. signals from d.c. A capacitor blocks steady d.c. (once it is charged, no current flows) but allows a.c. to pass, because it is continually charged and discharged as the voltage alternates. This is why capacitors are used for coupling and for separating a.c. from d.c. in circuits. The wording "filter a.c. from d.c." refers to this separating action, so Statement II is correct. Statement III: Capacitors can store charges. This is the basic function of a capacitor, using Q = CV. Statement III is correct. Step 3: Conclusion All three statements are correct, so the answer is D (I, II and III). Tip: Remember C = ε A / d. Bigger area means more capacitance, and bigger gap means less capacitance. Also remember the phrase "a capacitor blocks d.c., passes a.c." because it appears often in WASSCE and JAMB questions.

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