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ElectricalBasic Electrical
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If voltage drop across capcitor is 100V and current is 5A, what is value of capacitive reactance?

A

10╬й10\Omega10╬й

B

20╬й20\Omega20╬й

C

30╬й30\Omega30╬й

D

40╬й40\Omega40╬й

Correct Answer

тЪЩя╕П TE тАв Technical Concept & PrincipleElectricalBasic Electrical
Option B

20╬й20\Omega20╬й

Quick Summary:

Capacitive reactance (XCX_CXCтАЛ) is the opposition offered by a capacitor to the flow of alternating current. It is determined by the ratio of the RMS voltage drop across the capacitor (VCV_CVCтАЛ) to the RMS current flowing through it (ICI_CICтАЛ), expressed as XC=VCICX_C = \frac{V_C}{I_C}XCтАЛ=ICтАЛVCтАЛтАЛ.

тЪЩя╕ПTETechnical SolutionConcept & Principle
ЁЯТб Explanation

Capacitive reactance (XCX_CXCтАЛ) is the opposition offered by a capacitor to the flow of alternating current. It is determined by the ratio of the RMS voltage drop across the capacitor (VCV_CVCтАЛ) to the RMS current flowing through it (ICI_CICтАЛ), expressed as XC=VCICX_C = \frac{V_C}{I_C}XCтАЛ=ICтАЛVCтАЛтАЛ.

ЁЯФв Key Formulas

XC=VIX_C = \frac{V}{I}XCтАЛ=IVтАЛ тАФ Formula to calculate capacitive reactance when voltage and current are known.

XC=12╧АfCX_C = \frac{1}{2\pi f C}XCтАЛ=2╧АfC1тАЛ тАФ Fundamental formula relating reactance to frequency and capacitance.

тЪЩя╕П Working Principle

In an AC circuit, a capacitor stores and releases charge continuously as the voltage changes. This charging and discharging process results in a current that leads the voltage by 90 degrees. The opposition to this current flow, known as capacitive reactance, is inversely proportional to both the frequency of the supply and the capacitance of the component.

ЁЯУМ Key Points
  • тЦ╕

    Capacitive reactance is measured in Ohms (╬й).

  • тЦ╕

    It causes a phase shift where current leads voltage by 90┬░90┬░90┬░.

  • тЦ╕

    Reactance decreases as frequency increases.

  • тЦ╕

    For the given values, XC=100V5A=20╬йX_C = \frac{100V}{5A} = 20\OmegaXCтАЛ=5A100VтАЛ=20╬й.

тЬЕ Advantages
  • тЦ╕

    Used in AC filters to block DC.

  • тЦ╕

    Essential for phase shifting in motors.

тЭМ Disadvantages / Limitations
  • тЦ╕

    Reactance is frequency dependent, making it unstable in wide-band circuits.

  • тЦ╕

    Pure capacitors do not dissipate real power.

ЁЯЫая╕П Applications / Uses
  • тЦ╕

    Coupling capacitors in amplifiers.

  • тЦ╕

    Power factor correction units.

ЁЯУД Additional Information
  • тЦ╕

    The calculation is XC=1005=20╬йX_C = \frac{100}{5} = 20\OmegaXCтАЛ=5100тАЛ=20╬й.

  • тЦ╕

    Options A, C, and D are incorrect calculations based on the provided parameters.

ЁЯУК Diagram / Illustration
Capacitive ReactanceVoltage (V)Current (I)
тЬЕ

B is correct тАФ Using Ohm's law for AC circuits, XC=VI=1005=20╬йX_C = \frac{V}{I} = \frac{100}{5} = 20\OmegaXCтАЛ=IVтАЛ=5100тАЛ=20╬й.

Core Concepts Used
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Capacitive Reactance Ohm's Law for AC Phase Relationship
ЁЯТб EXAM TIP

Always remember that in an AC circuit with a capacitor, current leads the voltage. The reactance value XCX_CXCтАЛ must always be treated as a negative imaginary component in complex impedance calculations (тИТjXC-jX_CтИТjXCтАЛ).

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