# Class 12th Physics – 6 Alternating Current MCQs

#### A capacitor connected to an alternating voltage source resists any change in voltage.

A capacitor connected to an alternating voltage source resists any change in voltage.

#### When an inductor is connected to an alternating voltage source, the time lag between voltage and current is ____.

When an inductor is connected to an alternating voltage source, current lags behind voltage by one-fourth the time period.

#### The frequency of an alternating voltage is 60 Hz. Its angular frequency is ___ rad/s.

Angular frequency, ω = 2πν where ν is the frequency.

Hence, the angular frequency of the given alternating voltage is ω = 2 × 3.14 × 60

= 376.99 rad/s ≈ 377 rad/s

#### Capacitive reactance is the opposition of a capacitor to a change of electric voltage, due to its capacitance.

Capacitive reactance is the opposition of a capacitor to a change of electric voltage, due to its capacitance.

#### Inductive reactance is the opposition of a circuit element to a change of electric current or voltage, due to that element's inductance.

Inductive reactance is the opposition of a circuit element to a change of electric current or voltage, due to that element's inductance.

#### The Phasors for voltage and current of an AC circuit consisting of only a resistor ____.

The Phasors for voltage and current of an AC circuit consisting of only a resistor always rotate in the same direction as they are in phase.

#### Alternating voltages and currents are generally expressed in ___.

Alternating voltages and currents are generally expressed in sine functions.

#### Capacitive reactance of a capacitor connected to an alternating source of electricity is ____.

Capacitive reactance of a capacitor connected to an alternating source of electricity is given by 1/ωC.

#### In a circuit where AC voltage is applied to a resistor ____.

In a circuit where AC voltage is applied to a resistor, AC current is in phase with AC voltage.

#### The current driven by an AC voltage is called AC current.

The current driven by an AC voltage is called AC current.

#### When a capacitor is connected to an alternating voltage source, the average power dissipated in the circuit in a cycle is zero.

When a capacitor is connected to an alternating voltage source, the average power dissipated in the circuit in a cycle is zero. This is because the average of the sine function in a cycle is zero.

#### Inductive reactance in an alternating current circuit is directly proportional to ____.

Inductive reactance in an alternating current circuit is directly proportional to both inductance and frequency of the current.

#### A Phasor is a representation of a sine wave whose amplitude, phase and frequency are time invariant.

A Phasor is a representation of a sine wave whose amplitude, phase and frequency are time invariant.

#### AC is preferred to DC mainly because: (i) AC voltages can be easily and efficiently converted from lower to higher voltages (i) AC voltages can be easily and efficiently converted from higher to lower voltages

AC is preferred to DC mainly because AC voltages can be easily and efficiently converted from lower to higher voltages and vice versa.

#### In the case of a circuit with a pure resistor connected to an AC voltage, the ratio of instantaneous voltage to the instantaneous current is constant

In the case of a circuit with a pure resistor connected to an AC voltage, the ratio of instantaneous voltage to the instantaneous current is constant.

#### Capacitive reactance in an alternating current circuit is:

Capacitive reactance in an alternating current circuit is inversely proportional to the capacitance of the capacitor.

#### The average power supplied to an inductor over one complete cycle in an AC circuit consisting of an inductor is zero.

The average power supplied to an inductor over one complete cycle in an AC circuit consisting of an inductor is zero because the average of the sine function over a complete cycle is zero.

#### When a capacitor is connected to an alternating voltage source, the time lag between voltage and current is ____.

When a capacitor is connected to an alternating voltage source, voltage lags behind current by one-fourth the time period.

#### (i) The average power in a cycle due to an AC voltage source is zero. (ii) The average current in a cycle due to an AC voltage source is zero.

The average current in a cycle due to an AC voltage source is zero. However, the average power cannot be zero as the power is proportional to the square of current.

#### The device that is used to convert AC high voltages to AC high voltages and vice versa is a transformer.

The device that is used to convert AC high voltages to AC high voltages and vice versa is a transformer.

#### (i) The average current in a cycle due to an AC voltage source is zero. (ii) The AC current takes both positive and negative values.

The average current in a cycle due to an AC voltage source is zero. This is because; the AC current takes both positive and negative values.

#### Inductive reactance of a coil connected to an alternating source of electricity is ____.

Inductive reactance of a coil connected to an alternating source of electricity is the product of angular frequency of the AC voltage and the self inductance of the coil, given by XL = ωL.

#### The device that stores charge is ____.

A capacitor is a device that can store the charges.

#### The SI unit of inductive reactance is ____.

The SI unit of inductive reactance is ohm.

#### If only a resistor is connected in an AC circuit ____.

If only a resistor is connected in an AC circuit, current is in phase with voltage.

#### An inductor or a solenoid is an electrical component that can store energy in the magnetic field created by a varying current flowing through it.

An inductor or a solenoid is an electrical component that can store energy in the magnetic field created by a varying current flowing through it.

#### The expression for instantaneous alternating voltage for a circuit is given by V = 100 sin 770 t. Its angular frequency is ____ rad/s.

Given the instantaneous alternating voltage in the circuit is expressed as V = 50 sin 770 t

The standard expression for the voltage is V = Vo sinωt, where "ω" is the angular frequency

Comparing the two expressions we have ω = 770 rad/s

#### When an inductor is connected to an alternating voltage source, the phase lag between voltage and current is:

-When an inductor is connected to an alternating voltage source, current lags behind voltage by 90°.

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