Published by:
CGP EDU Academic Team
Published on: September 12, 2026
A
, F capacitor, a 0.10 H inductor and a
resistor are connected in series with an a.c. source of emf
.
Find (i) the frequency of the emf,
(ii) the reactance of the circuit,
(iii) the impedance of the circuit,
(iv) the current in the circuit and
(v) the phase angle. Also find the effective voltages across the capacitor, inductor and resistor.
Text Solution
Verified by ExpertsThe correct answer is:
A
Step 1: Find the Frequency of the EMF
Given the equation of emf is E = 310 sin(314t), the angular frequency \( \omega \) can be found where \( \omega = 314 \) rad/s.\
The frequency (f) can be calculated using the relation: \( f = \frac{\omega}{2\pi} = \frac{314}{2\pi} \approx 50 \) Hz.
Step 2: Calculate the Reactance of the Circuit
For the given components:
- Inductive reactance, \( X_L = \omega L = 314 \times 0.1 = 31.4 \; \Omega \)
- Capacitive reactance, \( X_C = \frac{1}{\omega C} = \frac{1}{314 \times 25 \times 10^{-6}} \approx 12.74 \; \Omega \)
Step 3: Calculate the Impedance of the Circuit
The total impedance (Z) in an RLC series circuit is given by:
\( Z = \sqrt{R^2 + (X_L - X_C)^2} \)
Substituting the values:
\( Z = \sqrt{(25)^2 + (31.4 - 12.74)^2} \approx \sqrt{625 + 339.76} \approx \sqrt{964.76} \approx 31.06 \; \Omega \)
Step 4: Calculate the Current in the Circuit
Using Ohm's law: \( I = \frac{E_{rms}}{Z} \), where: \( E_{rms} = \frac{E_{max}}{\sqrt{2}} = \frac{310}{\sqrt{2}} \approx 219.19 V \)
Thus: \( I = \frac{219.19}{31.06} \approx 7.05 A \)
Step 5: Calculate the Phase Angle
The phase angle (φ) can be calculated using:
\( \tan(\phi) = \frac{X_L - X_C}{R} \)
Substituting the known values:
\( \tan(\phi) = \frac{31.4 - 12.74}{25} = \frac{18.66}{25} \approx 0.7464 \rightarrow \phi = \tan^{-1}(0.7464) \approx 36.5° \)
Voltage calculations:
- Voltage across the resistor: \( V_R = I \cdot R = 7.05 \cdot 25 = 176.25 V \)
- Voltage across the inductor: \( V_L = I \cdot X_L = 7.05 \cdot 31.4 \approx 221.07 V \)
- Voltage across the capacitor: \( V_C = I \cdot X_C = 7.05 \cdot 12.74 \approx 89.78 V \)
Thus, overall results are:
- Frequency: 50 Hz,
- Reactance: Inductive \( X_L = 31.4 \; \Omega, X_C = 12.74 \; \Omega \),
- Impedance: \( Z \approx 31.06 \; \Omega \),
- Current: \( I \approx 7.05 A \),
- Phase Angle: \( \phi \approx 36.5° \),
- Voltages: \( V_R \approx 176.25 \, V, V_L \approx 221.07 \, V, V_C \approx 89.78 \, V \).
Given the equation of emf is E = 310 sin(314t), the angular frequency \( \omega \) can be found where \( \omega = 314 \) rad/s.\
The frequency (f) can be calculated using the relation: \( f = \frac{\omega}{2\pi} = \frac{314}{2\pi} \approx 50 \) Hz.
Step 2: Calculate the Reactance of the Circuit
For the given components:
- Inductive reactance, \( X_L = \omega L = 314 \times 0.1 = 31.4 \; \Omega \)
- Capacitive reactance, \( X_C = \frac{1}{\omega C} = \frac{1}{314 \times 25 \times 10^{-6}} \approx 12.74 \; \Omega \)
Step 3: Calculate the Impedance of the Circuit
The total impedance (Z) in an RLC series circuit is given by:
\( Z = \sqrt{R^2 + (X_L - X_C)^2} \)
Substituting the values:
\( Z = \sqrt{(25)^2 + (31.4 - 12.74)^2} \approx \sqrt{625 + 339.76} \approx \sqrt{964.76} \approx 31.06 \; \Omega \)
Step 4: Calculate the Current in the Circuit
Using Ohm's law: \( I = \frac{E_{rms}}{Z} \), where: \( E_{rms} = \frac{E_{max}}{\sqrt{2}} = \frac{310}{\sqrt{2}} \approx 219.19 V \)
Thus: \( I = \frac{219.19}{31.06} \approx 7.05 A \)
Step 5: Calculate the Phase Angle
The phase angle (φ) can be calculated using:
\( \tan(\phi) = \frac{X_L - X_C}{R} \)
Substituting the known values:
\( \tan(\phi) = \frac{31.4 - 12.74}{25} = \frac{18.66}{25} \approx 0.7464 \rightarrow \phi = \tan^{-1}(0.7464) \approx 36.5° \)
Voltage calculations:
- Voltage across the resistor: \( V_R = I \cdot R = 7.05 \cdot 25 = 176.25 V \)
- Voltage across the inductor: \( V_L = I \cdot X_L = 7.05 \cdot 31.4 \approx 221.07 V \)
- Voltage across the capacitor: \( V_C = I \cdot X_C = 7.05 \cdot 12.74 \approx 89.78 V \)
Thus, overall results are:
- Frequency: 50 Hz,
- Reactance: Inductive \( X_L = 31.4 \; \Omega, X_C = 12.74 \; \Omega \),
- Impedance: \( Z \approx 31.06 \; \Omega \),
- Current: \( I \approx 7.05 A \),
- Phase Angle: \( \phi \approx 36.5° \),
- Voltages: \( V_R \approx 176.25 \, V, V_L \approx 221.07 \, V, V_C \approx 89.78 \, V \).
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