Class 12 CBSE Physics Alternating Current Board Questions
Here we provide Class 12 Physics important notes,board questions and predicted questions with Answers for chapter Alternating Current. These important notes,board questions and predicted questions are based on CBSE board curriculum and correspond to the most recent Class 12 Physics syllabus. By practising these Class 12 materials, students will be able to quickly review all of the ideas covered in the chapter and prepare for the Class 12 Board examinations as well as other entrance exams such as NEET and JEE.
class 12 CBSE Physics Alternating Current BoardQuestions
Alternating Current BoardQuestions
2017
Q1
Device ‘X’ is connected to an ac source V = Vo sin ωt. The variation of voltage, current and power
in one cycle is shown in the following graph :
(a) Identify the device X’.
(b) Which of the curves A, B and C represent the voltage, current and the power consumed in the circuit ? Justify your answer.
(c) How does its impedance vary with frequency of the ac source ? Show graphically.
(d) Obtain an expression for the current in the circuit and its phase relation with ac voltage.
Solutions
(a) Identify the device X’.
(b) Which of the curves A, B and C represent the voltage, current and the power consumed in the circuit ? Justify your answer.
(c) How does its impedance vary with frequency of the ac source ? Show graphically.
(d) Obtain an expression for the current in the circuit and its phase relation with ac voltage.
Solutions
2018
Q1
The teachers of Geeta’s school took the students on a study trip to a power generating station,
located nearly 200 km away from the city. The teacher explained that electrical energy is
transmitted over such a long distance to their city, in the form of alternating current (ac) raised
to a high voltage. At the receiving end in the city, the voltage is reduced to operate the devices.
As a result, the power loss is reduced. Geeta listened to the teacher and asked questions about how
the ac is converted to a higher or lower voltage.
(a) Name the device used to change the alternating voltage to a higher or lower value. State one cause for power dissipation in this device.
(b) Explain with an example, how power loss is reduced if the energy is transmitted over long distances as an alternating current rather than a direct current.
(c) Write two values each shown by the teachers and Geeta.
Solutions
(a) Name the device used to change the alternating voltage to a higher or lower value. State one cause for power dissipation in this device.
(b) Explain with an example, how power loss is reduced if the energy is transmitted over long distances as an alternating current rather than a direct current.
(c) Write two values each shown by the teachers and Geeta.
Solutions
Q2
A device X is connected across an ac source of voltage V = Vo sin ωt. The current through X is given
as I= Io sin(ωt + π/2) :
(a) Identify the device X and write the expression for its reactance.
(b) Draw graphs showing variation of voltage and current with time over one cycle of ac, for X.
(c) How does the reactance of the device X vary with frequency of the ac ?
(d) Show this variation graphically. Draw the phasor diagram for the device X.
Solutions
(a) Identify the device X and write the expression for its reactance.
(b) Draw graphs showing variation of voltage and current with time over one cycle of ac, for X.
(c) How does the reactance of the device X vary with frequency of the ac ?
(d) Show this variation graphically. Draw the phasor diagram for the device X.
Solutions
2019
Q1
(a) In a series LCR circuit connected across an ac source of variable frequency, obtain the
expression for its impedance and draw a plot showing its variation with frequency of the ac source.
(b) What is the phase difference between the voltages across inductor and the capacitor at resonance in the LCR circuit ?
(c) When an inductor is connected to a 200 V dc voltage, a current of 1A flows through it. When the same inductor is connected to a 200 V, 50 Hz ac source, only 0.5 A current flows. Explain, why ? Also, calculate the self inductance of the inductor
Solutions
(i) Impedance is obstruction offered by an ac circuit in the flow of an ac current. It is a
combination
of resistance and reactance of the ac circuit. Its unit is ohm(Ω)
and it is given by
(b) What is the phase difference between the voltages across inductor and the capacitor at resonance in the LCR circuit ?
(c) When an inductor is connected to a 200 V dc voltage, a current of 1A flows through it. When the same inductor is connected to a 200 V, 50 Hz ac source, only 0.5 A current flows. Explain, why ? Also, calculate the self inductance of the inductor
Solutions
(i) Impedance is obstruction offered by an ac circuit in the flow of an ac current. It is a
combination
of resistance and reactance of the ac circuit. Its unit is ohm(Ω)
and it is given by
The required graph between the impedance Z and frequency f is as shown in the fig.
2020
Q1
Laminated iron sheets are used to minimize……………. currents in the core of a transformer
Solutions
Solutions
Eddy Current
Q2
A resistance R and a capacitor C are connected in series to a source V = Vo sin ωt. Find :
(a) The peak value of the voltage across the
(i) resistance and (ii) capacitor.
(b) The phase difference between the applied voltage and current. Which of them is ahead ?
Solutions
(a) The peak value of the voltage across the
(i) resistance and (ii) capacitor.
(b) The phase difference between the applied voltage and current. Which of them is ahead ?
Solutions
Q3
An a-particle is accelerated through a potential difference of 10 kV and moves along x-axis. It
enters in a region of uniform magnetic field B = 2 x 10-3 T acting along y-axis. Find the
radius of
its path. (Take path mass of α-particle = 6.4 x 10-2 kg )
With the help of a labelled diagram, explain the working of a step-up transformer. Give reasons to
explain the following :
(i) The core of the transformer is laminated.
(ii) Thick copper wire is used in windings.
Solutions
(i) The core of the transformer is laminated.
(ii) Thick copper wire is used in windings.
Solutions
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