Capacitance from charge and voltage: A capacitor has 25 V across its plates and stores a charge of 1500 µC. Compute the capacitance C (express your answer in appropriate SI units).
Electronics
Capacitors
Difficulty: Easy
Choose an option
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A60 pF
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B60 µF
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C16.67 mF
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D37.5 mF
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E6.0 µF
Answer
Correct Answer: 60 µF
Explanation
Introduction:Capacitance relates stored charge to voltage. For a lumped capacitor, the basic definition C = Q / V directly gives the required value when charge and voltage are known. Unit handling is crucial to avoid order-of-magnitude mistakes.
Given Data / Assumptions:
- Voltage V = 25 V
- Charge Q = 1500 µC
- Ideal capacitor with linear behavior
Concept / Approach:
Use the definition C = Q / V. Convert microcoulombs to coulombs: 1 µC = 1e-6 C. After calculation, express the result in a convenient unit (µF).
Step-by-Step Solution:
Convert Q: Q = 1500 µC = 1500 * 1e-6 C = 0.0015 CApply C = Q / VC = 0.0015 / 25 = 0.00006 FConvert to µF: 0.00006 F = 60 µFVerification / Alternative check:
Back-calculate charge with C = 60 µF at 25 V: Q = C * V = 60e-6 * 25 = 0.0015 C = 1500 µC, confirming correctness.
Why Other Options Are Wrong:
- 60 pF: Off by 10^6 due to unit confusion.
- 16.67 mF and 37.5 mF: Overestimates; would imply unrealistically large energy for given Q and V.
- 6.0 µF: Off by a factor of 10.
Common Pitfalls:
- Forgetting to convert µC to C before dividing.
- Confusing µF with mF and pF.
Final Answer:
60 µF