Units – Identify the correct SI unit of capacitance Statement: “The ohm is the unit of capacitance.” Mark the correct evaluation.
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AFalse
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BTrue
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CTrue only in cgs units
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DTrue when measuring reactive impedance
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ETrue for electrolytic capacitors
Answer
Correct Answer: False
Explanation
Introduction / Context:Unit clarity prevents misinterpretation of datasheets and calculations. Capacitance, resistance, and reactance have distinct SI units and symbols that must not be confused in design and testing.
Given Data / Assumptions:
- SI units are used: farad (F) for capacitance, ohm (Ω) for resistance, henry (H) for inductance.
- Capacitive reactance Xc = 1/(ωC) is measured in ohms but represents opposition to AC, not capacitance.
- No special unit systems assumed.
Concept / Approach:
Capacitance is defined as C = Q/V (coulombs per volt). The SI unit is the farad (F). Resistance is measured in ohms (Ω), and while capacitive reactance has units of ohms, that does not make “ohm” a unit of capacitance. Hence the statement is false.
Step-by-Step Solution:
Recall definitions: C = Q/V → unit F.Resistance R uses V = I * R → unit Ω.Capacitive reactance Xc = 1/(ωC) has unit Ω but is not a unit of C.Verification / Alternative check:
Check dimensional analysis: [F] = s^4 * A^2 / (m^2 * kg) in base units; [Ω] = kg * m^2 / (s^3 * A^2). They are not dimensionally equivalent.
Why Other Options Are Wrong:
No commonly used unit system assigns “ohm” to capacitance; electrolytic capacitors still use farads (often µF, mF). Reactance being in ohms does not redefine the unit of C.
Common Pitfalls:
Confusing reactance with capacitance; using Ω when a datasheet requires F, resulting in design errors.
Final Answer:
False.