Class 12 Physics | Electromagnetic Induction | Alternating current | 20 Assertion and Reason-Type questions | Solution with explanation

 

Class 12 Physics

• Electromagnetic Induction

• Alternating current

• 20 Assertion and Reason-Type

questions

• Solution with explanation

• Directions. In the following questions,statement
of assertion is followed by a statement of
reason. While answering a question, you are
required to choose the correct one out of the
given four responses and mark it as :-
• A, if both assertion and reason are true and
reason is the correct explanation of the
assertion.
• B, if both assertion and reason are true but
reason is not correct explanation of the
assertion.
• C, if assertion is true, but reason is false.
• D, if both assertion and reason are false.

1) Assertion : Faraday’s law are
consequence of conservation of
energy.
Reason :In a purely resistive ac
circuit, the current lags behind the
e.m.f. in phase.
1) A
2) B
3) C
4) D

2) Assertion :Eddy currents is
produced in any metallic conductor
when magnetic flux is changed
around it.
Reason :Electric potential
determines the flow of charge.
1. A
2. B
3. C
4. D

3) Assertion : A change in magnetic
flux will maintain an induced current in
the coil.
Reason :The presence of large
magnetic flux through a coil maintains
a current in the coil if the circuit is
continuous.
1)A           2) B
3) C          4) D

4) Assertion : When a bar magnet falls
freely along the axis of a solenoid held
vertically, its acceleration is less than the
acceleration due to gravity
Reason : The falling magnet induces
current in the solenoid and according to
lenz’s law, induced current opposes the
falling motion of the magnet.
1) A             2) B
3) C             4) D

5) Assertion : In the phenomenon of
mutual induction, self induction of
each of the coils persists.
Reason :Self induction arises when
strength of current in same coil
changes. In mutual induction, current
is changing in both the individual
coils.
1) A              2) B
3) C              4) D

6) Assertion : A metal piece and a non-
metal (stone) piece are dropped from
the same height near earth’s surface.
Both will reach the earth’s surface
simultaneously.
Reason :There is no effect of earth’s
magnetic field on freely falling body.
1) A             2) B
3) C             4) D

7) Assertion : Lenz’s law violates the
principle of conservation of energy.
Reason : Induced e.m.f., opposes
always the change in magnetic flux
responsible for its production.
1) A
2) B
3) C
4) D

8) Assertion: When a coil is moved out
of a magnetic field acting normally to its
plane, induced e.m.f is produced in it.
Reason : The induced e.m.f is
produced in the coil, when it is placed
inside the magnetic field .
1) A            2) B
3) C            4) D

9) Assertion : The possibility of an
electric bulb fusing is higher at the
time of switching ON and OFF.
Reason : Inductive effects produce a
surge at the time of switch OFF and
ON
1) A             2) B
3) C             4) D

10) Assertion :Inductance coil are
made of copper.
Reason :Induced current is more in
wire having less resistance.
1) A
2) B
3) C
4) D

11) Assertion : A capacitor blocks
d.c.
Reason : The capacitive reactance
is given by Xc = 1/ wc and for d.c, f=0
1) A
2) B
3) C
4) D

12) Assertion : At resonance, the
inductive reactance is equal and
opposite to the capacitive reactance.
Reason : In series LCR circuit, the
inductive reactance is equal and
opposite to the capacitive reactance.
1) A
2) B
3) C
4) D

13) Assertion :The alternating current
lags behind the e.m.f. by a phase angle
of π/2,when ac flows through an
inductor.
Reason :The inductive reactance
increases as the frequency of ac source
decreases.
1) A             2) B
3) C             4) D

14) Assertion : Transformers are
used only with an a.c source and not
with d.c source.
Reason : Only a.c can be stepped up
or stepped down by means of
transformers.
1) A
2) B
3) C
4) D

15) Assertion :If the frequency of
alternating current in an ac circuit
consisting of an inductance coil is
increased then current gets decreased.
Reason :The current is inversely
proportional to frequency of alternating
current.
1) A        2) B
3) C        4) D

16) Assertion :Average value of
ac over a complete cycle is
always zero.
Reason :Average value of ac is
always defined over half cycle.
1) A
2) B
3) C
4) D

17) Assertion : When ac circuit
contain resistor only, its power is
minimum.
Reason: Power of a circuit is
independent of phase angle.
1) A
2) B
3) C
4) D

18) Assertion: We use a thick wire in the
secondary of a step down transformer to
reduce the production heat.
Reason :When the plane of the armature
is parallel to the line of force of magnetic
field, the magnitude of induced e.m.f. is
maximum.
1) A          2) B
3) C          4) D

19) Assertion : A transformer can be
used to increase/decrease both voltage
and the current.
Reasons : In a transformer,
ep Ip = es Is and accordingly, if gain in
voltage, we lose in current and vice-
versa
1) A          2) B
3) C          4) D

20) Assertion : In series LCR -
circuit , the resonance occurs at
one frequency only.
Reason : At resonance, the
inductive reactance is equal and
opposite to the capacitive reactance.
1) A           2) B
3) C           4) D

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