View latest educational results 2026 of class 9th, 10th / Matric / SSC, Intermediate / HSSC / FA / FSc / Inter, 5th / Primary, 8th / Middle, DAE, DBA, D.COM, BA / BBA / BCom / BSc / B.Ed, MA / MSc / MBA / MIT / MCS, MBBA / M.Ed, LLB, Engineering, M.Phil, PhD from all BISE / boards and Universities by roll number & by name and check old result 2025 online.

Chapter 16 Alternating Current Physics 12th Class Punjab Short Questions

Question No. 1 - What is responsible factor for production of magnetic field in an atom?

Answer No. 1 - As Ampere suggested, a magnetic field is produced whenever an electrical charge in motion. The spinning and orbiting of the electrons of an atom produce a magnetic field as does electrical current flowing through a wire.

Question No. 2 - Define reactance of a capacitor.

Answer No. 2 - The opposition offered by a capacitor in the flow of A.C is called capacitive reactance. It varies inversely with the frequency of A.C.

Question No. 3 - What is meant by inductive and capacitive reactance?

Answer No. 3 - The measurement of opposition offered the inductor to the flow of alternating current is called inductive reactance. And the measurement of opposition offered by the capacitor to the flow of alternating current is called capacitive reactance.

Question No. 4 - What is choke?

Answer No. 4 - It is a coil of thick copper wire wound closely over soft iron laminated cores. It is used in AC circuits to limited current with extremely small wastage of energy as compare to a resistance.

Question No. 5 - What is the main reason for the world wide use of A.C.

Answer No. 5 - Because it can transmit to long distance easily and at a very low cost. Its power losses are very small and it may step up or step down by means of a transformer.

Question No. 6 - What is choke? Why it is used in AC circuit?

Answer No. 6 - A choke is a coil made of thick insulated copper wire wound closely in a large numbers of turns over a soft iron laminated core. It is used to control alternating current through a circuit without much loss of energy.

Question No. 7 - How many times per second will an incandescent lamp reach maximum brilliance when connected to a 50 Hz source? Explain.

Answer No. 7 - An incandescent lamp will reach maximum brilliance two time in cycle.One time for positive half cycle and one negative half cycle.

Question No. 8 - Write two properties of RLC series circuit.

Answer No. 8 - 1. The impedance of the circuit at resonance is minimum and
equal to R.
2. The power factor of RLC series circuit is 1.

Question No. 9 - Define impedance and resonant frequency.

Answer No. 9 - A measure of the opposition to the flow of charged is an AC circuit is called impedance. It is the combined effects of resistance and inductive and capacitive reactance is. Its unit is in ohms.
The frequency at which inductive and capacitive reactance become equal is called resonant frequency.

Question No. 10 - Define phase of alternating voltage.

Answer No. 10 - The angle θ=wt which specifies the instantaneous value of the alternating voltage or current is known as its phase.

Question No. 11 - Define Instantaneous Value and Peak value of current.

Answer No. 11 - The value of current or voltage at any any instant is called instantaneous value and the maximum value of current or voltage is called peak value.

Question No. 12 - Define alternating current.

Answer No. 12 - Alternating current is that which is produced by a voltage source whose polarity keeps on reserving with time.
I=IoSin2πft.

Question No. 13 - Write advantage and disadvantage of FM and AM.

Answer No. 13 - Advantage:
1. FM transmission frequencies are much higher and range
between 88 MHz to 108 MHz. AM transmission frequencies
range from 540 KHz to 1600 KHz.
2. FM radio waves are affected less by electrical
interference than AM radio waves.
Disadvantage:
1. FM have a short range than AM.
2. FM are less able to travel around obstacles such as
hills and large buildings.

Question No. 14 - Explain the principle of metal detector.

Answer No. 14 - Difference of frequencies of two LC oscillator circuit caused by placing the metallic object near one of them result to produce the beats.

Question No. 15 - Give any two properties of parallel resonant circuit.

Answer No. 15 - 1. At resonance frequency the circuit impedance is maximum.
2. At resonance the circuit current is minimum and is in
phase with the applied voltage.

Question No. 16 - Define reactance of an inductor and write its formula.

Answer No. 16 - The opposition offered by an inductor in the flow of AC is called inductive reactance which varies directly with frequency of A.C i.e xL= 2πfl.

Question No. 17 - What is the root mean square value of current?Explain.

Answer No. 17 - The square root of mean square values of current is called root mean square value of current. The average value of current over a cycle is zero but the power delivered during a cycle is not zero because power is I2R and the value are positive even for negative values of I.

Question No. 18 - Write down two advantage of use of three phase AC supply.

Answer No. 18 - 1. The main advantage of having three phase supply is that
the total load of the house or a factory is divided in
the three parts,so that none of the line is overloaded.
2. Three phase supply also provide 400 V Which can be used
to operate some special appliances which require 400 V
for their operation.

Question No. 19 - Define peak to peak value of A.C voltage.

Answer No. 19 - It is the sum of the positive and negative peak values. If Vo is the peak value of the voltage waveform then p-p value is 2Vo.

Question No. 20 - Why a transformer can not work on DC input supply? Explain.

Answer No. 20 - Since a transformer work on the principle of mutual induction and direct current can not induce emf as in mutual induction. So a transformer can not work on DC supply input supply.

Question No. 21 - What is modulation? Name its types.

Answer No. 21 - The process of combining the low frequency signal with a high frequency is called modulation. Its two types.
1. Amplitude Modulation
2. Frequency Modulation

Question No. 22 - Define choke and electromagnetic waves.

Answer No. 22 - A choke is a coil made of thick insulated copper wire wound closely in a large numbers of turns over a soft iron laminated core. It is used to control alternating current through a circuit without much loss of energy.

Question No. 23 - Define reactance. Describe the condition which will make the reactance small.

Answer No. 23 - The opposition offered by capacitor or conductor to the flow of alternating current is called reactance. For a capacitor reactance will be small when frequency is large and for an conductor reactance will be small when frequency is small.

Question No. 24 - What do you know mean by phase lag and phase lead?

Answer No. 24 - The angleθ which specifies the instantaneous value of the alternative voltage current, gives the phase lag or phase lead of one quantity over the other. The phase difference between two alternative quantity is observed at different points. The quantity which has greater phase at all points is said to be leading and the other is said to be lagging behind.

Question No. 25 - Differentiate between peak value and peak to peak value.

Answer No. 25 - Peak value: It is the highest value reached by the voltage or current in one cycle. It is donated by the V0.

Question No. 26 - Define impedance and write its SI unit.

Answer No. 26 - The combined effect of resistance and reactance is an AC circuit is known as impedance. It is donated by Z and its SI unit is ohm.

Question No. 27 - Define A.C current.

Answer No. 27 - A.C is that which is produced by a voltage source whose polarity keeps in reserving with time.

Question No. 28 - What is difference between A.C circuit and D.C circuit?

Answer No. 28 - In A.C circuit in addition to resistor. A Inductor and capacitor are used to control the current and voltage.

Question No. 29 - Write the conditions under which electromagnetic waves are produced from a source?

Answer No. 29 - Electromagnetic waves are produced according to the follow.
"A changing magnetic flux creates an electrical field and a changing electric flux creates magnetic field".

Previous Question

1-29

Next Question