MCQ Questions for Class 12 Physics Chapter 7 Alternating Current with Answers

Students are advised to practice the NCERT MCQ Questions for Class 12 Physics Chapter 7 Alternating Current with Answers Pdf free download is available here. MCQ Questions for Class 12 Physics with Answers are prepared as per the Latest Exam Pattern. Students can solve these Alternating Current Class 12 MCQs Questions with Answers and assess their preparation level.

Alternating Current Class 12 MCQs Questions with Answers

Solving the Alternating Current Multiple Choice Questions of Class 12 Physics Chapter 7 MCQ can be of extreme help as you will be aware of all the concepts. These MCQ Questions on Alternating Current Class 12 with answers pave for a quick revision of the Chapter thereby helping you to enhance subject knowledge. Have a glance at the MCQ of Chapter 7 Physics Class 12 and cross-check your answers during preparation.

I. Choose the correct answer

Question 1.
If the rms current in a 50 Hz ac circuit is 5 A, the value of the current 1/300 second after its value becomes zero is
(a) 5√2A
(b) 5√3 /2 A
(c) 5/6 A
(d) 5/√2 A

Answer

Answer: (b) 5√3 /2 A


Question 2.
To reduce the resonant frequency in an LCR series circuit with a generator
(a) the generator frequency should be reduced.
(b) another capacitor should be added in parallel to the first.
(c) the iron core of the inductor should be removed.
(d) dielectric in the capacitor should be removed.

Answer

Answer: (b) another capacitor should be added in parallel to the first.


Question 3.
The output of a step-down transformer is measured to be 24 V when connected to a 12 watt light bulb. The value of the peak current is
(a) 1/√2A
(b) √2A
(c) 2A
(d) 2√V2A

Answer

Answer: (a) 1/√2A


Question 4.
In an alternating current circuit consisting of elements in series, the current increases on increasing the frequency of supply. Which of the following elements are likely to constitute the circuit?
(a) Only resistor.
(b) Resistor and an inductor.
(c) Capacitor and an inductor.
(d) Only a capacitor.

Answer

Answer: (d) Only a capacitor.


Question 5.
As the frequency of an ac circuit increases, the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit?
(a) Inductor and capacitor.
(b) Resistor and inductor.
(c) Resistor and capacitor.
(d) None.

Answer

Answer: (a) Inductor and capacitor.


Question 6.
When an AC voltage of 220 V is applied to the capacitor C
(a) the maximum voltage between plates is 220 V.
(b) the current is in phase with the applied voltage.
(c) the charge on the plates is out of phase with the applied voltage.
(d) power delivered to the capacitor is zero.

Answer

Answer: (d) power delivered to the capacitor is zero.


Question 7.
Electrical energy is transmitted over large distances at high alternating voltages. Which of the following statements is incorrect?
(a) For a given power level, there is a lower current.
(b) Lower current implies less power loss.
(c) Transmission lines can be made thinner.
(d) It is easy to reduce the voltage at the receiving end using step-down transformers.

Answer

Answer: (c) Transmission lines can be made thinner.


Question 8.
In an ac circuit, V and i are given by V = 100 sin (100 t) volt and i = 100 sin (100 + \(\frac { π }{3}\)) mA. The power dissipated in circuit is
(a) 104 W
(b) 10 W
(c) 2.5 W
(d) 5 W

Answer

Answer: (c) 2.5 W


Question 9.
A small signal voltage V(t) = V0 sinω t is applied across an ideal capacitor C
(a) Current l (t) lags voltage V(t) by 90°.
(b) Over a full cycle the capacitor C does not consume any energy from the voltage source.
(c) Current l(t) is in phase with voltage V(t).
(d) Current l(t) leads voltage V(t) by 180°.

Answer

Answer: (b) Over a full cycle the capacitor C does not consume any energy from the voltage source.


Question 10.
The potential differences across the resistor, capacitor and inductor are 80 V, 40 V and 100 V, respectively in an LCR circuit. The power factor of this circuit is:
(a) 0.8
(b) 1.0
(c) 0.4
(d) 0.5

Answer

Answer: (a) 0.8


II. Fill in the Blanks

Question 1.
A steady (dc) current which when passed through a circuit for half the time period of ac will send the same amount of charge as is sent by ac through the same circuit for the same time is called ……………….

Answer

Answer: Average or mean value of ac


Question 2.
A steady current (dc) which when passed through a resistor in a given time produces the same heat as is produced by the ac. when passed through the same resistor for the same time is called ……………….

Answer

Answer: Root mean square value of ac


Question 3.
When ac flows through a pure resistor, emf and current are in ……………..

Answer

Answer: Phase


Question 4.
When ac flows through a pure inductor, emf …………….. current by an angle π/2.

Answer

Answer: Leads


Question 5.
When ac flows through a pure capacitor, emf ……………… current by an angle π/2.

Answer

Answer: Lags


Question 6.
…………….. is the ratio of the rms value to the mean or average value of ac.

Answer

Answer: Form factor


Question 7.
AC flows only on the surface of a wire. This effect is called ……………….. “effect”.

Answer

Answer: Skin


Question 8.
In ac-circuit, the average power consumed by a pure capacitor during one cycle in pure capacitance is ………………..

Answer

Answer: Zero


Question 9.
In ac-circuit, the average power consumed by a pure inductor during one cycle in pure capacitance is ………………..

Answer

Answer: Zero


Question 10.
If the power loss in a circuit is zero, the current is called ………………

Answer

Answer: Wattless current


Question 11.
A choke is preferred over resistance in an ac-circuit to decrease ac-current because it consumes practically ……………… power.

Answer

Answer: Zero


Question 12.
At resonance the current in a circuit is ……………..

Answer

Answer: Maximum


Question 13.
At resonance an LCR circuit behaves as a pure ……………….. circuit.

Answer

Answer: Resistive


Question 14.
The ratio \(\frac { ω_0 }{Δω}\) is called ……………….

Answer

Answer: Quality


Question 15.
Average power is equal to the product of virtual power and ………………

Answer

Answer: Power factor


Question 16.
……………….. is a device to convert a low voltage at high current, to a high voltage at low current and vice versa.

Answer

Answer: Transformer


Question 17.
AC dynamo is based on the principle of …………….. induction.

Answer

Answer: Electromagnetic


Question 18.
An ac dynamo has ………………. rings.

Answer

Answer: Slip


Question 19.
Maximum emf Induced in an ac dynamo is ……………………

Answer

Answer: nBAω


Question 20.
The core of a transformer is laminated to reduce …………………

Answer

Answer: Eddy currents


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