12th Class Physics Chapter 5 Short Questions with Answers Solved

Question: 1

Define reactance of a capacitor.

Answer: 1

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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: 2

What is choke?

Answer: 2

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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: 3

What is the root mean square value of current?Explain.

Answer: 3

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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: 4

Define phase of alternating voltage.

Answer: 4

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The angleθ=wt which specifies the instantaneous value of the alternating voltage or current is known as its phase.

Question: 5

Define reactance of an inductor and write its formula.

Answer: 5

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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 x_L= 2 $πfl.$

Question: 6

Write the conditions under which electromagnetic waves are produced from a source?

Answer: 6

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Electromagnetic waves are produced according to the follow.

"A changing magnetic flux creates an electrical field and a changing electric flux creates magnetic field".

Question: 7

What is the main reason for the world wide use of A.C/

Answer: 7

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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: 8

Write down two advantage of use of three phase AC supply.

Answer: 8

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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.
Three phase supply also provide 400 V Which can be used to operate some special appliances which require 400 V for their operation.

Question: 9

Write advantage and disadvantage of FM and AM.

Answer: 9

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Advantage:

FM transmission frequencies are much higher and range between 88 MHz to 108 MHz.AM transmission frequencies range from 540 KHz to 1600 KHz.
FM radio waves are affected less by electrical interference than AM radio waves.

Disadvantage:

FM have a short range than AM.
FM are less able to travel around obstacles such as hills and large buildings.

Question: 10

Explain the principle of metal detector.

Answer: 10

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Difference of frequencies of two LC oscillator circuit caused by placing the metallic object near one of them result to produce the beats.

Question: 11

Define reactance,Describe the condition which will make the reactance small.

Answer: 11

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The opposition offered by capacitor or inductor to the flow of alternating current is called reactance.For a capacitor reactance will be small when frequency is large and for an inductor reactance will be small when frequency is small.

Question: 12

Write two properties of RLC series circuit.

Answer: 12

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The impedance of the circuit at resonance is minimum and equal to R.
The power factor of RLC series circuit is 1.

Question: 13

What is responsible factor for production of magnetic field in an atom?

Answer: 13

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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: 14

Define peak to peak value of A.C voltage.

Answer: 14

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It is the sum of the positive and negative peak values,If V_ois the peak value of the voltage waveform then p-p value is 2V_o.

Question: 15

What is meant by inductive and capacitive reactance?

Answer: 15

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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: 16

What is choke?Why it is used in AC circuit?

Answer: 16

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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: 17

What is modulation?Name its types,

Answer: 17

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The process of combining the low frequency signal with a high frequency is called modulation.It is of two types.

Amplitude modulation
Frequency modulation.

Question: 18

Give any two properties of parallel resonant circuit.

Answer: 18

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At resonance frequency the circuit impedance is maximum.
At resonance the circuit current is minimum and is in phase with the applied voltage.

Question: 19

Define Instantaneous Value and Peak value of current.

Answer: 19

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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: 20

Define impedance and resonant frequency.

Answer: 20

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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 ohm''s.

The frequency at which inductive and capacitive reactance become equal is called resonant frequency.

Question: 21

Define alternating current.

Answer: 21

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Alternating current is that which is produced by a voltage source whose polarity keeps on reserving with time.

I=I_oSin2 $πft.$

Question: 22

What is difference between A.C circuit and D.C circuit?

Answer: 22

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In A.C circuit.in addition to resistor A,inductor and capacitor are used to control the current and voltage.

Question: 23

Define impedance and write its SI unit.

Answer: 23

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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: 24

What do you know mean by phase lag and phase lead?

Answer: 24

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The angleθ which specifiesthe instantaneous value of the alternative voltage current,gives the phase lag or phase lead of one quantity over the other.The phase differencebetween 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 laggingbehind.

Question: 25

How many times per second will an incandescent lamp reach maximum brilliance when connected to a 50 Hz source?Explain.

Answer: 25

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An incandescent lamp will reach maximum brilliance two time in cycle.One time for positive half cycle and one negative half cycle.

Question: 26

Define A.C current.

Answer: 26

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A.C is that which is produced by a voltage source whose polarity keeps in reserving with time.

Question: 27

Why a transformer can not work on DC input supply? Explain

Answer: 27

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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: 28

Define choke and electromagnetic waves.

Answer: 28

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