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The current in a circuit containing a ca...

The current in a circuit containing a capacitance `C` and a resistance `R` in series leads over the applied voltage of frequency `omega/(2pi)` by.

A

`tan^(-1)(1)/(omegaCR)`

B

`tan^(-1)(omegaCR)`

C

`tan^(-1)(omega1)/R`

D

`cos^(-1) (omegaCR)`

Text Solution

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The correct Answer is:
To solve the problem of determining how much the current in a circuit containing a capacitance \( C \) and a resistance \( R \) in series leads over the applied voltage of frequency \( \frac{\omega}{2\pi} \), we can follow these steps: ### Step-by-Step Solution: 1. **Understand the Circuit Configuration**: - The circuit consists of a resistor \( R \) and a capacitor \( C \) connected in series with an alternating current (AC) source. 2. **Identify the Voltage and Current Equations**: - The voltage across the circuit can be represented as: \[ V(t) = V_0 \sin(\omega t) \] - The current in the circuit can be expressed as: \[ I(t) = I_0 \sin(\omega t + \phi) \] - Here, \( \phi \) is the phase angle by which the current leads or lags the voltage. 3. **Determine the Phase Relationship**: - In an RC circuit, the current leads the voltage. The relationship between the voltages across the resistor \( V_R \) and the capacitor \( V_C \) can be analyzed using phasor diagrams. 4. **Use Phasor Diagram**: - The phasor for the current \( I \) is taken as the reference phasor. The voltage across the resistor \( V_R \) is in phase with the current, while the voltage across the capacitor \( V_C \) lags the current by \( 90^\circ \). 5. **Apply the Relationships**: - The relationship between the voltages can be expressed as: \[ \tan(\theta) = \frac{V_C}{V_R} \] - From the definitions, we know: \[ V_R = I \cdot R \quad \text{and} \quad V_C = I \cdot X_C \] - Here, \( X_C = \frac{1}{\omega C} \) is the capacitive reactance. 6. **Substituting Values**: - Substitute \( V_R \) and \( V_C \) into the tangent equation: \[ \tan(\theta) = \frac{I \cdot X_C}{I \cdot R} = \frac{X_C}{R} \] - This simplifies to: \[ \tan(\theta) = \frac{1}{\omega C R} \] 7. **Find the Phase Angle**: - Therefore, the phase angle \( \theta \) can be expressed as: \[ \theta = \tan^{-1}\left(\frac{1}{\omega C R}\right) \] ### Final Answer: The current in the circuit leads over the applied voltage by: \[ \theta = \tan^{-1}\left(\frac{1}{\omega C R}\right) \]
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