Alternating Current
- A coil of inductive reactance 31 Ω has a resistance of 8 Ω. It is placed in series with a condenser of capacitative reactance 25Ω. The combination is connected to an a.c. source of 110 volt. The power factor of the circuit is
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Power factor,
φ = R √[ωL -(1/ωC)²] + R² = 8 = 8 √(31 - 25)² + 8² √6² + 8² = 8 = 0.8 10
Correct Option: B
Power factor,
φ = R √[ωL -(1/ωC)²] + R² = 8 = 8 √(31 - 25)² + 8² √6² + 8² = 8 = 0.8 10
- A transformer having efficiency of 90% is working on 200V and 3kW power supply. If the current in the secondary coil is 6A, the voltage across the secondary coil and the current in the primary coil respectively are :
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Efficiency η = VsIs ⇒ 0.9 = Vs(6) VpIp 3 × 103
⇒ Vs = 450 V
As VpIp = 3000 soIp = 3000 = 3000 A = 15 A Vp 200
Correct Option: B
Efficiency η = VsIs ⇒ 0.9 = Vs(6) VpIp 3 × 103
⇒ Vs = 450 V
As VpIp = 3000 soIp = 3000 = 3000 A = 15 A Vp 200
- The time constant of C–R circuit is
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The time constant for resonance circuit, = CR Growth of charge in a circuit containing capacitance and resistance is given by the formula,
q = q0(1 - e-t/CR)
CR is known as time constant in this formula.Correct Option: C
The time constant for resonance circuit, = CR Growth of charge in a circuit containing capacitance and resistance is given by the formula,
q = q0(1 - e-t/CR)
CR is known as time constant in this formula.
- An LCR series circuit is connected to a source of alternating current. At resonance, the applied voltage and the current flowing through the circuit will have a phase difference of
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At resonance, ωL = 1 ωC
The circuit behaves as if it contains R only. So, phase difference = 0
At resonance, impedance is minimum Zmin = R and current is maximum, given byImax = E = E Zmin R
It is interesting to note that before resonance the current leads the applied emf, at resonance it is in phase, and after resonance it lags behind the emf. LCR series circuit is also called as acceptor circuit and parallel LCR circuit is called rejector circuit.
Correct Option: D
At resonance, ωL = 1 ωC
The circuit behaves as if it contains R only. So, phase difference = 0
At resonance, impedance is minimum Zmin = R and current is maximum, given byImax = E = E Zmin R
It is interesting to note that before resonance the current leads the applied emf, at resonance it is in phase, and after resonance it lags behind the emf. LCR series circuit is also called as acceptor circuit and parallel LCR circuit is called rejector circuit.
- In an experiment, 200 V A.C. is applied at the ends of an LCR circuit. The circuit consists of an inductive reactance (XL ) = 50 Ω, capacitive reactance (XC ) = 50 Ω and ohmic resistance (R) = 10 Ω. The impedance of the circuit is
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Given : Supply voltage (Vac) = 200 V
Inductive reactance (XL) = 50 Ω
Capacitive reactance (XC) = 50 Ω
Ohmic resistance (R) = 10 Ω.
We know that impedance of the LCR circuit (Z) =
√{(XL - XC)² + R² }
√{(50 - 50)² + (10)² } = 10 ΩCorrect Option: A
Given : Supply voltage (Vac) = 200 V
Inductive reactance (XL) = 50 Ω
Capacitive reactance (XC) = 50 Ω
Ohmic resistance (R) = 10 Ω.
We know that impedance of the LCR circuit (Z) =
√{(XL - XC)² + R² }
√{(50 - 50)² + (10)² } = 10 Ω
