In the electric field of a point charge \[q\], a certain charge is carried from point \[A\] to \[B\], \[C\], \[D\] and \[E\]. Then the work done [NCERT 1980]

Is zero along all the paths \[AB,\ AC,\ AD\] and \[AE\]

The adjoining figure shows two bulbs B1 and B2 resistor R and an inductor L. When the switch S is turned off [CPMT 1989]

B2 dies out promptly but B1 with some delay

Both B1 and B2 die out promptly

Both B1 and B2 die out with some delay

B1 dies out promptly but B2 with some delay

B2 dies out promptly but B1 with some delay

An L-R circuit has a cell of e.m.f. E, which is switched on at time t = 0. The current in the circuit after a long time will be [MP PET 2003]

\[\frac{E}{\sqrt{{{L}^{2}}+{{R}^{2}}}}\]

Two coils of self-inductance \[{{L}_{1}}\] and \[{{L}_{2}}\] are placed closer to each other so that total flux in one coil is completely linked with other. If \[M\] is mutual inductance between them, then [DCE 2002]

\[M={{({{L}_{1}}{{L}_{2}})}^{2}}\]

\[M=\sqrt{{{L}_{1}}{{L}_{2}}}\]

\[M={{({{L}_{1}}{{L}_{2}})}^{2}}\]

A solenoid of length l metre has self-inductance L henry. If number of turns are doubled, its self inductance [MP PMT 2001]

Becomes \[\frac{L}{\sqrt{2}}\] henry

Which of the following is wrong statement [AMU 1995]

Inserting an iron core in a coil increases its coefficient of self induction

An emf can be induced between the ends of a straight conductor by moving it through a uniform magnetic field

The self-induced emf produced by changing current in a coil always tends to decrease the current

Inserting an iron core in a coil increases its coefficient of self induction

According to Lenz's law, the direction of the induced current is such that it opposes the flux change that causes it

Mutual inductance of two coils can be increased by [MP PET 1994]

Winding the coils on wooden core

Decreasing the number of turns in the coils

Increasing the number of turns in the coils

Winding the coils on wooden core

There are three wire MO, NO and PQ, wires MO and NO are fixed and perpendicular to each other. Wire PQ moves with a constant velocity v as shown in the figure and resistance per unit length of each wire is\[\lambda \]and magnetic field exists perpendicular and inside the paper then. Which of the following is wrong?

current in loop is anticlockwise

magnitude of current in the loop is\[\frac{Bv}{\lambda (\sqrt{2}+1)}\]

current in the loop is independent of time.

magnitude of current decreases as time increases.

A conducting disc of conductivity a has a radius 'a' and thickness 'f. If the magnetic field B is applied in a direction perpendicular to the plane of the disc changes with time at the rate of \[\frac{dB}{dt}=\alpha \]. Calculate the power dissipated in the disc due to the induced current.

\[\frac{\pi t\sigma {{a}^{4}}}{4}{{\alpha }^{2}}\]

\[\frac{\pi t\sigma {{a}^{4}}}{8}{{\alpha }^{2}}\]

\[\frac{\pi t\sigma {{a}^{4}}}{4}{{\alpha }^{2}}\]

\[\frac{\pi t\sigma {{a}^{4}}}{2}{{\alpha }^{2}}\]

\[\frac{2\pi t\sigma {{a}^{4}}}{3}{{\alpha }^{2}}\]

A straight conducting metal wire is bent in the given shape and the loop is closed. Dimensions are as shown in the figure. Now the assembly is heated at a constant rate \[~dT/dt\text{ }=\text{ }l{}^\circ C/s\]. The assembly is kept in a uniform magnetic field B=1 T, perpendicular into the paper. Find the current in the loop at the moment, when the heating starts. Resistance of the loop is \[10\Omega \] at any temperature. Coefficient of linear expansion \[\alpha ={{10}^{-6}}/{}^{o}C\].

\[1.5\times {{10}^{-6}}\,A\]clockwise

\[1.5\times {{10}^{-6}}\,A\] anticlockwise

\[1.5\times {{10}^{-6}}\,A\]clockwise

\[0.75\times {{10}^{-6}}\,A\] anticlockwise

\[0.75\times {{10}^{-6}}\,A\]clockwise

A conducting wire of mass m slides down two smooth conducting bars, set at an angle 0 to the horizintal as shown in Fig. The separation between the bars is\[l\]. The system is located in the magnetic field B, perpendicular to the plane of the sliding wire and bars. The constant velocity of the wire is

\[\frac{mg\,R\,\sin \theta }{B{{l}^{2}}}\]

\[\frac{mg\,R\,\sin \theta }{{{B}^{2}}{{l}^{2}}}\]

\[\frac{mg\,R\,\sin \theta }{B{{l}^{2}}}\]

\[\frac{mg\,R\,\sin \theta }{{{B}^{2}}{{l}^{5}}}\]

\[\frac{mg\,R\,\sin \theta }{B{{l}^{4}}}\]

A wooden stick of length \[3\ell \]is rotated about an end with constant angular velocity \[\omega \] in a uniform magnetic field B perpendicular to the plane of motion. If the upper one third of its length is coated with copper, the potential difference across the whole length of the stick is

\[\frac{B\omega {{\ell }^{2}}}{2}\]

\[\frac{9B\omega {{\ell }^{2}}}{2}\]

\[\frac{4B\omega {{\ell }^{2}}}{2}\]

\[\frac{5B\omega {{\ell }^{2}}}{2}\]

\[\frac{B\omega {{\ell }^{2}}}{2}\]

Two identical cycle wheels (geometrically) have different number of spokes connected from center to rim. One is having 20 spokes and the other having only 10 (the rim and the spokes are resistance less). One resistance of value R is connected between center and rim. The current in R will be

double in the first wheel than in the second wheel

four times in the first wheel than in the second wheel

will be double in the second wheel than that of the first wheel

will be equal in both these wheels

A rectangular coil ABCD is rotated anticlockwise with a uniform angular velocity about the axis shown in diagram below. The axis of rotation of the coil as well as the magnetic field B are horizontal. The induced e.m.f. in the coil would be maximum when [Haryana CEE 1996; MP PMT 1992, 94, 99]

The plane of the coil makes an angle of 45° with the magnetic field

The plane of the coil is horizontal

The plane of the coil makes an angle of 45° with the magnetic field

The plane of the coil is at right angles to the magnetic field

The plane of the coil makes an angle of 30° with the magnetic field

In an AC circuit, the voltage applied is\[E={{E}_{0}}\sin \omega t\]. The resulting current in the circuit is\[I={{I}_{0}}\sin (\omega t-\pi /2)\]. The power consumption in the circuit is given by

\[P=\frac{{{E}_{0}}{{I}_{0}}}{2}\]

\[P=\sqrt{2}\]\[{{E}_{0}}{{I}_{0}}\]

\[P=\frac{{{E}_{0}}{{I}_{0}}}{\sqrt{2}}\]

Assertion : Self-inductance is called the inertia of electricity. Reason : Self-inductance is the phenomenon, according to which an opposing induced e.m.f. is produced in a coil as a result of change in current or magnetic flux linked in the coil.

If assertion is true but reason is false.

If both assertion and reason are true and the reason is the correct explanation of the assertion.

If both assertion and reason are true but reason is not the correct explanation of the assertion.

If assertion is true but reason is false.

If the assertion and reason both are false.

In the diagram shown if a bar magnet is moved along the common axis of two single turn coils A and B in the direction of arrow [Kerala (Engg.) 2001]

Current is induced only in A & not in B

Induced currents in A & B are in the same direction

Current is induced only in B and not in A

Induced currents in A & B are in opposite directions

12583 + Mcqs in Physics in Joint Entrance Exam - Main (JEE Main) Page 249 McqOptions

12401.	Two charges \[+3.2\times {{10}^{-19}}C\] and \[-3.2\times {{10}^{-9}}C\] kept 2.4 Å apart forms a dipole. If it is kept in uniform electric field of intensity \[4\times {{10}^{5}}volt/m\] then what will be its electrical energy in equilibrium [MP PMT 2003]
A.	\[+3\times {{10}^{-23}}J\]
B.	\[-3\times {{10}^{-23}}J\]
C.	\[-6\times {{10}^{-23}}J\]
D.	\[-2\times {{10}^{-23}}J\]
Answer» C. \[-6\times {{10}^{-23}}J\]

Discussion

12402.	A thin metal plate P is inserted half way between the plates of a parallel plate capacitor of capacitance C in such a way that it is parallel to the two plates. The capacitance now becomes [Orissa JEE 2002]
A.	C
B.	C/2
C.	4C
D.	None of these
Answer» B. C/2

Discussion

12403.	A particle \[A\] has charge \[+q\] and a particle \[B\] has charge \[+\,4q\] with each of them having the same mass \[m\]. When allowed to fall from rest through the same electric potential difference, the ratio of their speed \[\frac{{{v}_{A}}}{{{v}_{B}}}\] will become [BHU 1995; MNR 1991; UPSEAT 2000; Pb PET 2004]
A.	\[2:1\]
B.	\[1:2\]
C.	\[1:4\]
D.	\[4:1\]
Answer» C. \[1:4\]

Discussion

12404.	A parallel plate air capacitor has a capacitance of \[100\mu \mu F\]. The plates are at a distance \[d\]apart. If a slab of thickness \[t(t\le d)\]and dielectric constant 5 is introduced between the parallel plates, then the capacitance will be [MP PMT 2003]
A.	\[50\mu \mu F\]
B.	\[100\mu \mu F\]
C.	\[200\mu \mu F\]
D.	\[500\mu \mu F\]
Answer» D. \[500\mu \mu F\]

Discussion

12405.	Two capacitors each of capacity \[2\mu F\] are connected in parallel. This system is connected in series with a third capacitor of \[12\mu F\] capacity. The equivalent capacity of the system will be [MP PET 1990; MP PMT 1990]
A.	\[16\mu F\]
B.	\[13\mu F\]
C.	\[4\mu F\]
D.	\[3\mu F\]
Answer» E.

Discussion

12406.	In a parallel plate capacitor of capacitance C, a metal sheet is inserted between the plates, parallel to them. If the thickness of the sheet is half of the separation between the plates. The capacitance will be [KCET 2001]
A.	\[\frac{C}{2}\]
B.	\[\frac{3C}{4}\]
C.	\[4C\]
D.	\[2C\]
Answer» E.

Discussion

12407.	The unit of electric permittivity is [MP PET 2003]
A.	\[Volt/{{m}^{2}}\]
B.	Joule/coulomb
C.	Farad/m
D.	Henry/m
Answer» D. Henry/m

Discussion

12408.	In the electric field of a point charge \[q\], a certain charge is carried from point \[A\] to \[B\], \[C\], \[D\] and \[E\]. Then the work done [NCERT 1980]
A.	Is least along the path \[AB\]
B.	Is least along the path \[AD\]
C.	Is zero along all the paths \[AB,\ AC,\ AD\] and \[AE\]
D.	Is least along \[AE\]
Answer» D. Is least along \[AE\]

Discussion

12409.	The adjoining figure shows two bulbs B1 and B2 resistor R and an inductor L. When the switch S is turned off [CPMT 1989]
A.	Both B1 and B2 die out promptly
B.	Both B1 and B2 die out with some delay
C.	B1 dies out promptly but B2 with some delay
D.	B2 dies out promptly but B1 with some delay
Answer» D. B2 dies out promptly but B1 with some delay

Discussion

12410.	An L-R circuit has a cell of e.m.f. E, which is switched on at time t = 0. The current in the circuit after a long time will be [MP PET 2003]
A.	Zero
B.	\[\frac{E}{R}\]
C.	\[\frac{E}{L}\]
D.	\[\frac{E}{\sqrt{{{L}^{2}}+{{R}^{2}}}}\]
Answer» C. \[\frac{E}{L}\]

Discussion

12411.	Two coils of self-inductance \[{{L}_{1}}\] and \[{{L}_{2}}\] are placed closer to each other so that total flux in one coil is completely linked with other. If \[M\] is mutual inductance between them, then [DCE 2002]
A.	\[M={{L}_{1}}{{L}_{2}}\]
B.	\[M={{L}_{1}}/{{L}_{2}}\]
C.	\[M=\sqrt{{{L}_{1}}{{L}_{2}}}\]
D.	\[M={{({{L}_{1}}{{L}_{2}})}^{2}}\]
Answer» D. \[M={{({{L}_{1}}{{L}_{2}})}^{2}}\]

Discussion

12412.	A solenoid of length l metre has self-inductance L henry. If number of turns are doubled, its self inductance [MP PMT 2001]
A.	Remains same
B.	Becomes 2L henry
C.	Becomes 4L henry
D.	Becomes \[\frac{L}{\sqrt{2}}\] henry
Answer» D. Becomes \[\frac{L}{\sqrt{2}}\] henry

Discussion

12413.	Pure inductance of 3.0 H is connected as shown below. The equivalent inductance of the circuit is [MNR 1998; AIEEE 2002]
A.	1 H
B.	2 H
C.	3 H
D.	9 H
Answer» B. 2 H

Discussion

12414.	Which of the following is wrong statement [AMU 1995]
A.	An emf can be induced between the ends of a straight conductor by moving it through a uniform magnetic field
B.	The self-induced emf produced by changing current in a coil always tends to decrease the current
C.	Inserting an iron core in a coil increases its coefficient of self induction
D.	According to Lenz's law, the direction of the induced current is such that it opposes the flux change that causes it
Answer» C. Inserting an iron core in a coil increases its coefficient of self induction

Discussion

12415.	The energy stored in a 50 mH inductor carrying a current of 4 A will be [MP PET 1999]
A.	0.4 J
B.	4.0 J
C.	0.8 J
D.	0.04 J
Answer» B. 4.0 J

Discussion

12416.	The inductance of a coil is \[60\,\mu H\]. A current in this coil increases from 1.0 A to 1.5 A in 0.1 second. The magnitude of the induced e.m.f. is [MP PMT 1995]
A.	\[60\times {{10}^{-6}}\,V\]
B.	\[300\times {{10}^{-4}}\,V\]
C.	\[30\times {{10}^{-4}}\,V\]
D.	\[3\times {{10}^{-4}}\,V\]
Answer» E.

Discussion

12417.	The current flowing in a coil of self inductance 0.4 mH is increased by 250 mA in 0.1 sec. The e.m.f. induced will be [MP PMT 1994]
A.	+ 1 V
B.	? 1 V
C.	+ 1 mV
D.	? 1 mV
Answer» E.

Discussion

12418.	A 50 mH coil carries a current of 2 ampere. The energy stored in joules is [MP PET/PMT 1988; MP PET 2005]
A.	1
B.	0.1
C.	0.05
D.	0.5
Answer» C. 0.05

Discussion

12419.	Mutual inductance of two coils can be increased by [MP PET 1994]
A.	Decreasing the number of turns in the coils
B.	Increasing the number of turns in the coils
C.	Winding the coils on wooden core
D.	None of the above
Answer» C. Winding the coils on wooden core

Discussion

12420.	Two circuits have coefficient of mutual induction of 0.09 henry. Average e.m.f. induced in the secondary by a change of current from 0 to 20 ampere in 0.006 second in the primary will be [MP PET 1992]
A.	120 V
B.	80 V
C.	200 V
D.	300 V
Answer» E.

Discussion

12421.	If a current of 3.0 amperes flowing in the primary coil is reduced to zero in 0.001 second, then the induced e.m.f. in the secondary coil is 15000 volts. The mutual inductance between the two coils is [MP PMT 1989, 91]
A.	0.5 henry
B.	5 henry
C.	1.5 henry
D.	10 henry
Answer» C. 1.5 henry

Discussion

12422.	When the current in a coil changes from 8 ampere to 2 ampere in \[3\times {{10}^{-2}}\]second, the e.m.f. induced in the coil is \[2\ volt\]. The self-inductance of the coil (in millihenry) is [MNR 1991; UP SEAT 2000; Pb PET 2004]
A.	1
B.	5
C.	20
D.	10
Answer» E.

Discussion

12423.	A conducting ring of radius r with a conducting spoke OA is in pure rolling on a horizontal surface in a region having a uniform magnetic field B as shown, v being the velocity of the centre of the ring. Then the potential difference \[{{V}_{0}}-{{V}_{A}}\]is:
A.	\[\frac{Bvr}{2}\]
B.	\[\frac{3Bvr}{2}\]
C.	\[\frac{Bvr}{2}\]
D.	\[\frac{-3Bvr}{2}\]
Answer» D. \[\frac{-3Bvr}{2}\]

Discussion

12424.	There are three wire MO, NO and PQ, wires MO and NO are fixed and perpendicular to each other. Wire PQ moves with a constant velocity v as shown in the figure and resistance per unit length of each wire is\[\lambda \]and magnetic field exists perpendicular and inside the paper then. Which of the following is wrong?
A.	current in loop is anticlockwise
B.	magnitude of current in the loop is\[\frac{Bv}{\lambda (\sqrt{2}+1)}\]
C.	current in the loop is independent of time.
D.	magnitude of current decreases as time increases.
Answer» E.

Discussion

12425.	An electric potential difference will be induced between the ends of the conductor as shown in the diagram, when the conductor moves in the direction
A.	P
B.	Q
C.	L
D.	M
Answer» E.

Discussion

12426.	A horizontal straight wire 20m long extending from east to west falling with a speed of 5.0 m/s, at right angles to the horizontal component of the earth's magnetic field \[0.30\times {{10}^{-4}}\,Wb/{{m}^{2}}\]. The instantaneous value of the e.m.f. induced in the wire will be
A.	3 mV
B.	4.5 mV
C.	1.5mV
D.	6.0 mV
Answer» B. 4.5 mV

Discussion

12427.	A varying current in a coil changes from 10A to zero in 0.5 sec. If the average e.m.f induced in the coil is 220V, the self-inductance of the coil is
A.	5 H
B.	6 H
C.	11 H
D.	12 H
Answer» D. 12 H

Discussion

12428.	A conducting square frame of side' a' and a long staight wire carrying current I are located in the same plane as shown in the figure. The frame moves to the right with a constant velocity ?V?. The emf induced in the frame will be proportional to
A.	\[\frac{1}{{{(2x-a)}^{2}}}\]
B.	\[\frac{1}{{{(2x+a)}^{2}}}\]
C.	\[\frac{1}{(2x-a)(2x+a)}\]
D.	\[\frac{1}{{{x}^{2}}}\]
Answer» D. \[\frac{1}{{{x}^{2}}}\]

Discussion

12429.	A conducting disc of conductivity a has a radius 'a' and thickness 'f. If the magnetic field B is applied in a direction perpendicular to the plane of the disc changes with time at the rate of \[\frac{dB}{dt}=\alpha \]. Calculate the power dissipated in the disc due to the induced current.
A.	\[\frac{\pi t\sigma {{a}^{4}}}{8}{{\alpha }^{2}}\]
B.	\[\frac{\pi t\sigma {{a}^{4}}}{4}{{\alpha }^{2}}\]
C.	\[\frac{\pi t\sigma {{a}^{4}}}{2}{{\alpha }^{2}}\]
D.	\[\frac{2\pi t\sigma {{a}^{4}}}{3}{{\alpha }^{2}}\]
Answer» B. \[\frac{\pi t\sigma {{a}^{4}}}{4}{{\alpha }^{2}}\]

Discussion

12430.	A straight conducting metal wire is bent in the given shape and the loop is closed. Dimensions are as shown in the figure. Now the assembly is heated at a constant rate \[~dT/dt\text{ }=\text{ }l{}^\circ C/s\]. The assembly is kept in a uniform magnetic field B=1 T, perpendicular into the paper. Find the current in the loop at the moment, when the heating starts. Resistance of the loop is \[10\Omega \] at any temperature. Coefficient of linear expansion \[\alpha ={{10}^{-6}}/{}^{o}C\].
A.	\[1.5\times {{10}^{-6}}\,A\] anticlockwise
B.	\[1.5\times {{10}^{-6}}\,A\]clockwise
C.	\[0.75\times {{10}^{-6}}\,A\] anticlockwise
D.	\[0.75\times {{10}^{-6}}\,A\]clockwise
Answer» B. \[1.5\times {{10}^{-6}}\,A\]clockwise

Discussion

12431.	A conducting wire of mass m slides down two smooth conducting bars, set at an angle 0 to the horizintal as shown in Fig. The separation between the bars is\[l\]. The system is located in the magnetic field B, perpendicular to the plane of the sliding wire and bars. The constant velocity of the wire is
A.	\[\frac{mg\,R\,\sin \theta }{{{B}^{2}}{{l}^{2}}}\]
B.	\[\frac{mg\,R\,\sin \theta }{B{{l}^{2}}}\]
C.	\[\frac{mg\,R\,\sin \theta }{{{B}^{2}}{{l}^{5}}}\]
D.	\[\frac{mg\,R\,\sin \theta }{B{{l}^{4}}}\]
Answer» B. \[\frac{mg\,R\,\sin \theta }{B{{l}^{2}}}\]

Discussion

12432.	A wooden stick of length \[3\ell \]is rotated about an end with constant angular velocity \[\omega \] in a uniform magnetic field B perpendicular to the plane of motion. If the upper one third of its length is coated with copper, the potential difference across the whole length of the stick is
A.	\[\frac{9B\omega {{\ell }^{2}}}{2}\]
B.	\[\frac{4B\omega {{\ell }^{2}}}{2}\]
C.	\[\frac{5B\omega {{\ell }^{2}}}{2}\]
D.	\[\frac{B\omega {{\ell }^{2}}}{2}\]
Answer» D. \[\frac{B\omega {{\ell }^{2}}}{2}\]

Discussion

12433.	Two identical cycle wheels (geometrically) have different number of spokes connected from center to rim. One is having 20 spokes and the other having only 10 (the rim and the spokes are resistance less). One resistance of value R is connected between center and rim. The current in R will be
A.	double in the first wheel than in the second wheel
B.	four times in the first wheel than in the second wheel
C.	will be double in the second wheel than that of the first wheel
D.	will be equal in both these wheels
Answer» E.

Discussion

12434.	A vertical ring of radius r and resistance R falls vertically. It is in contact with two vertical rails which are joined at the top. The rails are without friction and resistance. There is a horizontal uniform magnetic field of magnitude B perpendicular to the plane of the ring and -the rails. When the speed of the ring is v, the current in the top horizontal of the rail section is
A.	0
B.	\[\frac{2Brv}{R}\]
C.	\[\frac{4Brv}{R}\]
D.	\[\frac{8Brv}{R}\]
Answer» E.

Discussion

12435.	The figure shows a conducting loop consisting of half circle of area \[A=0.06\,{{m}^{2}}\] and three straight segments. The half circle lies in a uniform changing magnetic field \[B=4{{r}^{2}}+2t+5\] (SI unit), where t is the time in second. An ideal battery E=2V is connected as shown and the total resistance of the wire is \[2\Omega \]. The net current in the loop is at t=5 second is:
A.	1A
B.	1.5A
C.	0.26A
D.	0.10A
Answer» D. 0.10A

Discussion

12436.	In the figure the flux through the loop perpendicular to the plane of the coil and directed into the paper is varying according to the relation \[\phi =6{{t}^{2}}+7t+1\] where \[\phi \] is in milli weber and t is in second. The magnitude of the emf induced in the loop at t=2 s and the direction of induce current through R are
A.	39 m V; right to left
B.	39 m V; left to right
C.	31 m V; right to left
D.	31 m V; left to right
Answer» E.

Discussion

12437.	A conducting square loop is placed in a magnetic field B with its plane perpendicular to the field. The sides of the loop start shrinking at a constant rate \[\alpha \]. The induced emf in the loop at an instant when its side is 'a' is
A.	\[2a\alpha B\]
B.	\[{{a}^{2}}\alpha B\]
C.	\[2{{a}^{2}}\alpha B\]
D.	\[a\alpha B\]
Answer» B. \[{{a}^{2}}\alpha B\]

Discussion

12438.	When a wire loop is rotated in a magnetic field, the direction of induced e.m.f. changes once in each [MP PMT 1991, 04]
A.	\[\frac{1}{4}\] revolution
B.	\[\frac{1}{2}\] revolution
C.	1 revolution
D.	2 revolution
Answer» C. 1 revolution

Discussion

12439.	A two metre wire is moving with a velocity of 1 m/sec perpendicular to a magnetic field of 0.5 weber/m2. The e.m.f. induced in it will be [MP PMT/PET 1998; Pb PET 2003]
A.	0.5 volt
B.	0.1 volt
C.	1 volt
D.	2 volt
Answer» D. 2 volt

Discussion

12440.	A rectangular coil ABCD is rotated anticlockwise with a uniform angular velocity about the axis shown in diagram below. The axis of rotation of the coil as well as the magnetic field B are horizontal. The induced e.m.f. in the coil would be maximum when [Haryana CEE 1996; MP PMT 1992, 94, 99]
A.	The plane of the coil is horizontal
B.	The plane of the coil makes an angle of 45° with the magnetic field
C.	The plane of the coil is at right angles to the magnetic field
D.	The plane of the coil makes an angle of 30° with the magnetic field
Answer» B. The plane of the coil makes an angle of 45° with the magnetic field

Discussion

12441.	A conductor of length \[l\] and mass m can slide without any friction along the two vertical conductors connected at the top through a capacitor (figure). A uniform magnetic field B is set \[\bot \]up 1 to the plane of paper. The acceleration of the conductor
A.	Is constant
B.	Increases
C.	Decreases
D.	Cannot say
Answer» B. Increases

Discussion

12442.	In an AC circuit, the voltage applied is\[E={{E}_{0}}\sin \omega t\]. The resulting current in the circuit is\[I={{I}_{0}}\sin (\omega t-\pi /2)\]. The power consumption in the circuit is given by
A.	\[P=0\]
B.	\[P=\frac{{{E}_{0}}{{I}_{0}}}{2}\]
C.	\[P=\sqrt{2}\]\[{{E}_{0}}{{I}_{0}}\]
D.	\[P=\frac{{{E}_{0}}{{I}_{0}}}{\sqrt{2}}\]
Answer» B. \[P=\frac{{{E}_{0}}{{I}_{0}}}{2}\]

Discussion

12443.	Assertion : Self-inductance is called the inertia of electricity. Reason : Self-inductance is the phenomenon, according to which an opposing induced e.m.f. is produced in a coil as a result of change in current or magnetic flux linked in the coil.
A.	If both assertion and reason are true and the reason is the correct explanation of the assertion.
B.	If both assertion and reason are true but reason is not the correct explanation of the assertion.
C.	If assertion is true but reason is false.
D.	If the assertion and reason both are false.
Answer» C. If assertion is true but reason is false.

Discussion

12444.	In the diagram shown if a bar magnet is moved along the common axis of two single turn coils A and B in the direction of arrow [Kerala (Engg.) 2001]
A.	Current is induced only in A & not in B
B.	Induced currents in A & B are in the same direction
C.	Current is induced only in B and not in A
D.	Induced currents in A & B are in opposite directions
Answer» E.

Discussion

12445.	A stretched rubber has [AIIMS 2000]
A.	Increased kinetic energy
B.	Increased potential energy
C.	Decreased kinetic energy
D.	Decreased potential energy
Answer» C. Decreased kinetic energy

Discussion

12446.	When a force is applied on a wire of uniform cross-sectional area \[3\times {{10}^{-6}}\,{{m}^{2}}\]and length 4m, the increase in length is 1 mm. Energy stored in it will be \[(Y=2\times {{10}^{11}}\,N/{{m}^{2}})\] [MP PET 1995; Pb. PET 2002]
A.	6250 J
B.	0.177 J
C.	0.075 J
D.	0.150 J
Answer» D. 0.150 J

Discussion

12447.	Two wires of same diameter of the same material having the length l and 2l. If the force F is applied on each, the ratio of the work done in the two wires will be [MP PET 1989]
A.	0.0430555555555556
B.	1 : 4
C.	2 : 1
D.	1 : 1
Answer» B. 1 : 4

Discussion

12448.	When shearing force is applied on a body, then the elastic potential energy is stored in it. On removing the force, this energy
A.	Converts into kinetic energy
B.	Converts into heat energy
C.	Remains as potential energy
D.	None of the above
Answer» C. Remains as potential energy

Discussion

12449.	A copper wire of length 4.0m and area of cross-section \[1.2\,c{{m}^{2}}\] is stretched with a force of \[4.8\times {{10}^{3}}\] N. If Young?s modulus for copper is \[1.2\times {{10}^{11}}\,N/{{m}^{2}},\] the increase in the length of the wire will be [MP PET 2001]
A.	1.33 mm
B.	1.33 cm
C.	2.66 mm
D.	2.66 cm
Answer» B. 1.33 cm

Discussion

12450.	The breaking stress of a wire depends upon [AIIMS 2002]
A.	Length of the wire
B.	Radius of the wire
C.	Material of the wire
D.	Shape of the cross section
Answer» D. Shape of the cross section

Discussion

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