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Published on: 02/11/2025
Download CBSE Class 12th Standard CBSE Physics question papers, sample papers, important questions, and previous year solved papers in PDF format. Get free study materials, NCERT solutions, and exam preparation resources for Class 12th Standard CBSE Physics
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1.
In a series LCR circuit, \({ V }_{ L }={ V }_{ C }\neq { V }_{ R }.\) What is the value of power factor?
2.
What is the minimum value of power factor? When does it occur?
3.
What is the average power consumed in a circuit consisting of resistanceless inductance?
4.
In a pure LC circuit, what is the energy stored when peak current is \({ I }_{ 0 }\) ?
5.
What is meant by wattless current?
6.
Where is the power dissipation in an alternating current circuit? In resistance? In inductance? In capacitance?
7.
Why are parallel resonance circuits called rejector circuits/filter circuits/antiresonance circuits?
8.
An electrical element X when connected to an alternating voltage source has current through it leading the voltage by \(\pi /2\) radian. Identify X and write an expression for its reactance.
9.
How is capacitative reactance affected when frequency of a.c. supply is tripled?
10.
How does inductive reactance vary when frequency of a.c. source in the circuit is halved?
11.
Why is choke coil needed in the use of fluorescent tubes with ac mains?
12.
Why cannot a transformer be used to step up d.c. voltage?
13.
The inductance of a coil is 0.25H. Calculate its inductive reactance in a.c. of frequency 50 Hz.
14.
Why is induced emf called back e.m.f. ?
15.
The self induced emf in a coil when current charges on it is given by.
16.
What are the dimensions of inductance?
17.
Why does a metallic piece become very hot when it is surrounded by a coil carrying high frequency alternating current?
18.
What is the basic cause of induced e.m.f.?
19.
A vertical metallic pole falls down through the plane of magnetic meridian. Will any e.m.f. be induced between its ends ?
20.
A transformer is an electric device that is used for.......................... . It..........................work on....................... .
21.
In d.c. motor, we use........................to determine the direction of.......................... .
22.
In a.c. generator, we use..........................to determine the direction of............................. .
23.
When a coil carrying current is.........................., it experiences.................which.....................the coil. This is the principle of...................... .
24.
A d.c. generator, ............................arrangement of a.c. generator is replaced by......................... .
25.
A d.c. motor converts..............................into............................ .
26.
In hydroelectric power station, ....................of falling water is converted into................. .
27.
An a.c. generator is based on the phenomenon of................................. .
28.
An a.c. generator is a machine that produces.............................from........................ .
29.
A series resonance circuit is called an.........................and a...........................is called................... .
30.
Ohmic resistance R can reduce.....................but inductor L can reduce.....................only.
31.
A condenser.....................a.c. to pass through but......................d.c.
32.
The dimensions of inductive.........................and..........................are the same as those of..................... .
33.
In an a.c. circuit containing L only, alternating current...................alternating voltage by a phase angle of......................... .
34.
In an a.c. circuit containing R only......................and.......................are in.........................phase.
35.
220 V a.c. means...........................And and a.c. of 1 means...................... .
36.
The r.m.s. value or...................value or.................value od a.c. is..................thye peak value of a.c.
37.
Ordinary d.c. ammeter and d.c. voltage, when used in .......................record.......................reading.
38.
The....................of alternating current varies.......................with time and its.........................is reversed........................ .
39.
Coefficient of mutual inductance of two coils is numerically .................... linked with one coil when .............. flows through ............. .
40.
Self inductance of a solenoid varies..............as the..............of total number of turns in the solenoid.
41.
Self induction of a coil is said to be............when a current change.................through the coil induces..................in the coil.
42.
If \(\omega \) is angular frequency of a.c, then the reactance offered by inductance L and capacitance C are XL =....................and XC =.................... .
43.
Eddy currents are the currents..................when................changes.
44.
Lenz's law is..............with the law...................... .
45.
According to.............law, the polarity of.............is such that it..............responsible for.............. .
46.
An e.m.f. is induced in a coil when...................linked with the coil...............with................. .
47.
One weber is the amount of........over an area of............held normal to a uniform................. .
48.
A coil having n turns and resistance R is connected with a galvanometer of resistance 4R. This combination is moved in time t seconds from a magnetic flux \({ \phi }_{ 1 }\) Weber to \({ \phi }_{ 2 }\) Weber. The induced current in the circuit is :
\(\frac { { \phi }_{ 2 }-{ \phi }_{ 1 } }{ 5Rnt } \)
\(\frac { -n\left( { \phi }_{ 2 }-{ \phi }_{ 1 } \right) }{ 5Rt } \)
\(\frac { -\left( { \phi }_{ 2 }-{ \phi }_{ 1 } \right) }{ Rnt } \)
\(\frac { -n\left( { \phi }_{ 2 }-{ \phi }_{ 1 } \right) }{ Rt } \)
49.
A conducting circuit loop is placed in a uniform magnetic field of induction B tesla with its plane normal to the field. Now, the radius of the loop starts sharinking at the rate dr/dt. The induced emf at the instant when the radius is R is:
\(\pi rB\left( \frac { dr }{ dt } \right) \)
\(2\pi rB\left( \frac { dr }{ dt } \right) \)
\(\pi r^{ 2 }\left( \frac { dr }{ dt } \right) \)
\(\left( \frac { \pi r^{ 2 } }{ 2 } \right) ^{ 2 }\left( \frac { dr }{ dt } \right) \)
50.
To reduce the reasonant frequency in an LCR series circuit with a generator
the generator frequency should be reduced
another capacitor should be added in parallel to the first
the iron core of the inductor should be removed
dielectric in the capacitor should be removed
51.
An alternating current generator has an internal resistance Rg and an internal reactance Xg. It is used to supply power to a passive load consisting of a resistance Rg and a reactance XL. For maximum power to be delivered from the generator to the load, the value of XL is equal to
zero
Xg
-Xg
Rg
52.
A circular coil expands radially in a region of magnetic field and no electromotive force is produced in the coil. This can be because
the magentic field is constant
the magnetic field is in the same plane as the circular coil and it may or may not vary
the magnetic field has a perpendicular componet whose magnitude is decreasing suitably
there is a constant magnetic field in the perpendicular direction.
53.
A metal plate is getting heated. It can be because
a direct current is passing through the plate
it is placed in a time varying magnetic field
it is placed in a space varying magnetic field, but does not vary with time
a current is passing through the plate
54.
A transformer is an electric device used for
producing direct current
producing alternating current
changing d.c. into a.c.
changing a.c. voltages
55.
The efficiency of d.c.motor id given by \(\eta \) =
\(\frac { back \ e.m.f. }{ applied \ e.m.f. } \)
\(\frac { applied \ e.m.f }{ back \ e.m.f. } \)
\(back \ e.m.f.\ \times \ applied \ e.m.f.\)
none of the above
1.
\(V_L=V_C ; X_L=X_C ; Z=R ; \cos \phi=\frac{R}{Z}=1\)
2.
Zero, in a pure inductor and in a pure capacitor.
3.
Zero, because through resistance less inductance,
\(\phi=90^{\circ} \text { and } p=E_v I_v \cos 90^{\circ}=0\)
4.
Total energy stored in inductor = \(\frac{1}{2} L I_0^2\)
5.
Wattless current is that which involves no consumption of power per cycle for its maintenance in the circuit.
6.
Power is dissipated in an a.c. circuit in resistance only.
7.
This is because parallel resonance circuits reject the current corresponding to parallel resonance frequencies. These circuits are used in the transmitting circuits.
8.
As current through element X leads the alternating voltage applied by \(\pi /2\) radian, therefore X is a pure capacitance. Its reactance is \(X_C=\frac{1}{\omega C}=\frac{1}{2 \pi v C} .\)
9.
\(X_C=\frac{1}{\omega C}=\frac{1}{2 \pi \omega v C}\) therefore, when v is tripled
10.
\(X_L=\omega L=2 \pi v L,\)
11.
A choke coil reduces the voltage across the fluorescent tube without wastage of power.
12.
This is because d.c. voltage cannot produce a changing magnetic flux required in the working of a transformer.
13.
\(X_L=\omega L=2 \pi \nu L=2 \pi \times 50 \times 0.25\)
\(=25 \pi \mathrm{ohm}\)
14.
Induced emf is called back emf as it opposes the growth as well as decay of current in the circuit.
15.
\(e=-L \frac{d l}{d t}\)
Where symbols have usual meaning.
16.
\(e=L \frac{d l}{d t}, L=\frac{e \cdot d t}{d I}=\frac{W}{q} \cdot \frac{d t}{d I}\)
\(L=\frac{\left(M L^2 T^{-2}\right) T}{(A T) A}=\left[M L^2 T^{-2} A^{-2}\right]\)
17.
High frequency alternating current passed through the coil surrounding the metal piece produces eddy currents in the metal piece. The eddy currents produce joule heating in the metal piece on account of its resistance.
18.
Change in magnetic flux linked with the circuit.
19.
No, because the pole intercepts neither H nor V.
20.
( )
changing a.c. voltages; does not; d.c.
21.
( )
Flemingls left hand rule; force on the wire carrying current
22.
( )
Fleming's right hand rule; induced current
23.
( )
held in a magnetic field; torque; rotates; d.c. motor
24.
( )
direct current energy; mechanical energy of rotation
25.
( )
direct current energy; mechanical energy
26.
( )
kinetic energy; electrical energy
27.
( )
electromagnetic induction
28.
( )
alternating current energy; mechanical energy
29.
( )
acceptor circuit; parallel resonance circuit; rejector / filter circuit.
30.
( )
both a.c. and d.c. ; a.c.
31.
( )
allows; blocks
32.
( )
reactance; capacitative reactance; resistance
33.
( )
lags behind; \({ 90 }^{ \circ }\)
34.
( )
alternating current; alternating voltage; same
35.
( )
Ev = 220V; Iv = 1A
36.
( )
virtual; effective; 0.707 times
37.
( )
a.c. circuits; zero
38.
( )
magnitude; continuously; direction; periodically
39.
( )
equal to amount of magnetic flux; unit current; the other coil
40.
( )
directly; square
41.
( )
one henry; at the rate of 1 ampere/sec; an emf of 1 volt.
42.
( )
XL= \(\omega \)L; XC = \(\frac { 1 }{ \omega C } \)
43.
( )
induced in the body of a conductor; amount of magnetic flux linked with the conductor.
44.
( )
in accordance; of conservation of energy.
45.
( )
Lenz's; emf induced; opposes the change in magnetic flux; its production.
46.
( )
amount of magnetic flux; changes; time.
47.
( )
magnetic flux; 1m2; magnetic field of 1 Wb/m2
48.
(b)
\(\frac { -n\left( { \phi }_{ 2 }-{ \phi }_{ 1 } \right) }{ 5Rt } \)
49.
(b)
\(2\pi rB\left( \frac { dr }{ dt } \right) \)
50.
(b)
another capacitor should be added in parallel to the first
51.
(c)
-Xg
52.
(b)
the magnetic field is in the same plane as the circular coil and it may or may not vary
53.
(a)
a direct current is passing through the plate
54.
(d)
changing a.c. voltages
55.
(a)
\(\frac { back \ e.m.f. }{ applied \ e.m.f. } \)
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