Alternating Current (22 Dec) - Live Session - NEET 2020 Contact Number: 9667591930 / 8527521718

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An A.C. circuit containing only capacitance, the

current :

1. lags the voltage by 90°

2. leads the voltage by 90°

3. remains in phase with voltage

4. leads the voltage in 180°

A choke coil has:

1. Low inductance and low resistance

2. High inductance and high resistance

3. Low inductance and high resistance

4. High inductance and low resistance

Turn ratio in a step-up transformer is 1: 2 if a

Lechlanche cell of 1.5 V is connected across the

input, then the voltage across the output will be:

1. 0.1 V

2. 1.5 V

3. 0.75 V

4. zero

In the circuit shown below what will be the

reading of the voltmeter and ammeter ?

(Total impedance of circuit Z = 100$\mathrm{\Omega}$)

1. 200 V, 1A

2. 800 V, 2A

3. 100 V, 2A

4. 220 V, 2.2 A

In a circuit the coil of a choke :

1. decreases the current

2. increases the current

3. has high resistance to D. C. circuit

4. no effect with the current

In a circuit, the current lags behind the voltage

by a phase difference of p /2, the circuit will

contain which of the following : [2001]

1. only R

2. only C

3. R and C

4. only L

The coefficient of mutual inductance, when

magnetic flux changes by 2 × 10^{–2} Wb and

current changes by 0.01 A is

1. 8 henry

2. 4 henry

3. 3 henry

4. 2 henry

In an ideal parallel LC circuit, the capacitor is

charged by connecting it to a D.C. source which

is then disconnected. The current in the circuit:

1. becomes zero instantaneously

2. grows monotonically

3. decays monotonically

4. oscillates instantaneously

A capacitor of capacitance 2µF is connected in

the tank circuit of an oscillator oscillating with a

frequency of 1 kHz. If the current flowing in the

circuit is 2 m A, the voltage across the capacitor

will be :

1. 0.16 V

2. 0.32 V

3. 79.5 V

4. 159 V

A 50 Hz a.c. source of 20 volt is connected across

R and C as shown in figure. The voltage across

R is 12 volt. The voltage across C is :

1. 8 V

2. 16 V

3. 10 V

4. not possible to determine unless values of

R and C are given

In an AC circuit the potential differences across

an inductance and resistance joined in series

are respectively 16 V and 20 V. The total potential

difference of the source is [2007]

1. 20.0 V

2. 25.6 V

3. 31.9 V

4. 53.5 V

With the decrease of current in the primary coil

from 2 amperes to zero value in 0.01s the emf

generated in the secondary coil is 1000 volts.

The mutual inductance of the two coils is

1. 1.25 H

2. 2.50 H

3. 5.00 H

4. 10.00 H

An AC source of angular frequency $\mathrm{\omega}$ is fed

across a resistor R and a capacitor C in series.

The current registered is I. If now the

frequency of source is changed to $\mathrm{\omega}$/3 (but

maintaining the same voltage), the current in

the circuit is found to be halved. Calculate

the ratio of reactance to resistance at the

original frequency $\mathrm{\omega}$

1. $\sqrt{\frac{3}{5}}$

2. $\sqrt{\frac{2}{5}}$

3. $\sqrt{\frac{1}{5}}$

4. $\sqrt{\frac{4}{5}}$

If an AC main supply is given to be 220 V. The

average emf during a positive half cycle will be

1. 198 V

2. 220 V

3. 240 V

4. 220 $\sqrt{2}$V

A coil has an inductance of 0.7 henry and is

joined in series with a resistance of 220 $\mathrm{\Omega}$. When

the alternating emf of 220 V at 50 Hz is applied to

it then the phase through which current lags

behind the applied emf and the wattless

component of current in the circuit will be

respectively

1. 30°, 1 A

2. 45°, 0.5 A

3. 60°, 1.5 A

4. none of these

An inductor and a resistor in series are

connected to an A.C. supply of variable

frequency. As the frequency of the source is

increased, the phase angle between current and

the potential difference across L will:

1. first increase and then decrease

2. first decrease and then increase

3. go on decreasing

4. go on increasing

In a AC circuit the voltage and current are

described

by V = 200sin$\left(319\mathrm{t}-\frac{\mathrm{\pi}}{6}\right)$ volts

and i = 50sin$\left(314\mathrm{t}+\frac{\mathrm{\pi}}{6}\right)$ mA

respectively. The average power dissipated in

the circuit is :

1. 2.5 watts

2. 5.0 watts

3. 10.0 watts

4. 50.0 watts

If we decrease the frequency of the applied A.C. with a purely capacitive load, do (1) the amplitude of V${}_{\mathrm{c}}$ and (2) amplitude of I${}_{\mathrm{c}}$increase, decrease of remain the same.

1. (1) increase (2) same

2. (1) same (2) increase

3. (1) same (2) decrease

4. (1) decrease (2) same

An inductor coil of inductance L is cut into two

equal parts and both the parts are connected in

parallel. The net inductance is : [2011]

1. L

2. L/2

3. L/4

4. 2 L.

The current in resistance R at resonance is

1. zero

2. minimum but finite

3. maximum but finite

4. infinite

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