Do you need help learning for your Class 12 Physics exam? Students may want to download NCERT MCQ Questions for Class 12 Physics Chapter 7 Alternating Current with Answers Pdf free download. This Alternating Current Class 12 MCQs Questions with Answers can help understand the concepts score better in your Class 12 Physics Exam, so make sure you practice these! Check out chapter-wise MCQ Questions for Class 12 Physics with Answers.
Alternating Current Class 12 MCQs Questions with Answers
Solve this Alternating Current Multiple Choice Questions of Class 12 Physics Chapter 7 MCQ, so as not to miss out on any concept from being clear about what they mean!
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
This NCERT MCQ Questions for Class 12 Physics Chapter 7 Alternating Current with Answers Pdf free download has been put together to help students understand the CBSE Class 12 Physics Alternating Current MCQs Multiple Choice Questions with Answers. Hope you found this helpful!