Alternating Current

In a LCR circuit capacitance is changed from C to 2C. For the resonant frequency to remain unchanged, the inductance should be changed from L to

• 4L

• 2L

• L/2

• L/2

In an a.c. circuit the voltage applied is E = E₀ sinπt. The resulting current in the circuit is I = I₀ sin .The power consumption in the circuit is given by

• 

• P = zero

• 
• 

In an LCR series a.c. circuit, the voltage across each of the components, L, C and R is 50 V. The voltage across the LC combination will be

• 50 V

• 50√2 V

• 100 V

• 100 V

Two voltameters one of copper and another of silver, are joined in parallel. When a total charge q flows through the voltameters, equal amount of metals are deposited. If the electrochemical equivalents of copper and silver are z₁ and z₂ respectively the charge which flows through the silver voltameter is

Alternating current can not be measured by D.C. ammeter because

• A.C. cannot pass through D.C.

• A.C. changes direction

• average value of current for complete cycle is zero

• average value of current for complete cycle is zero

In a series resonant LCR circuit, the voltage across R is 100 volts and R = 1 kΩ with C = 2µF. The resonant frequency ω is 200 rad/s. At resonance the voltage across L is

• 4 × 10−3 V

• 2.5 × 10⁻² V

• 40 V

• 40 V

The phase difference between the alternating current and emf is π/2. Which of the following cannot be the constituent of the circuit?

• C alone

• R.L

• L.C

• L.C

A circuit has a resistance of 12 Ω and an impedance of 15 Ω. The power factor of the circuit will be

• 0.8

• 0.4

• 1.25

• 1.25

A current I flows along the length of an infinitely long, straight, thin walled pipe. Then 

• the magnetic field is zero only on the axis of the pipe

• the magnetic field is different at different points inside the pipe

• the magnetic field at any point inside the pipe is zero

• the magnetic field at any point inside the pipe is zero

In a series LCR circuit, R = 200 Ω and the voltage and the frequency of the main supply is 220 V and 50 Hz respectively. On taking out the capacitance from the circuit the current lags behind the voltage by 30º. On taking out the inductor from the circuit the current leads the voltage by 30º. The power dissipated in the LCR circuit is

• 305 W

• 210 W

• zero

• zero