question_answer 1)
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)
\[2a\alpha B\] done
clear
B)
\[{{a}^{2}}\alpha B\] done
clear
C)
\[2{{a}^{2}}\alpha B\] done
clear
D)
\[a\alpha B\] done
clear
View Solution play_arrow
question_answer 2)
A rectangular loop is present in the magnetic field region of an infinite long wire. Now the loop is being rotated as shown in the figure. Then the induced current in side AD will be
A)
along DA done
clear
B)
along AD done
clear
C)
zero done
clear
D)
None of these done
clear
View Solution play_arrow
question_answer 3)
A rod PQ of length L moves with a uniform velocity v parallel to a long straight wire carrying a current i, the end P remaining at a distance r from the wire. The emf induced across the rod is
A)
\[\frac{{{\mu }_{0}}i{{v}^{2}}}{2\pi }ln\,\left( \frac{r+L}{R} \right)\] done
clear
B)
\[\vec{B}\] done
clear
C)
\[\frac{{{\mu }_{0}}iv}{2\pi }ln\,\left( \frac{r+L}{R} \right)\] done
clear
D)
\[\frac{{{\mu }_{0}}iv}{2\pi }ln\,\left( \frac{{{r}^{2}}+{{L}^{2}}}{{{L}^{2}}} \right)\] done
clear
View Solution play_arrow
question_answer 4)
A coil having n turns and resistance \[R\Omega \]. Is connected with a galvanometer of resistance\[4R\,\Omega \]. This combination is moved in time t second from a magnetic flux \[{{\phi }_{1}}\]weber to\[{{\phi }_{2}}\] weber. The induced current in the circuit is
A)
\[-\frac{{{\phi }_{2}}-{{\phi }_{1}}}{5\,Rnt}\] done
clear
B)
\[-\frac{n({{\phi }_{2}}-{{\phi }_{1}})}{5\,Rt}\] done
clear
C)
\[-\frac{({{\phi }_{2}}-{{\phi }_{1}})}{\,Rnt}\] done
clear
D)
\[-\frac{n({{\phi }_{2}}-{{\phi }_{1}})}{\,Rt}\] done
clear
View Solution play_arrow
question_answer 5)
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)
\[\frac{\pi t\sigma {{a}^{4}}}{8}{{\alpha }^{2}}\] done
clear
B)
\[\frac{\pi t\sigma {{a}^{4}}}{4}{{\alpha }^{2}}\] done
clear
C)
\[\frac{\pi t\sigma {{a}^{4}}}{2}{{\alpha }^{2}}\] done
clear
D)
\[\frac{2\pi t\sigma {{a}^{4}}}{3}{{\alpha }^{2}}\] done
clear
View Solution play_arrow
question_answer 6)
Shown in the figure is a circular loop of radius r and resistance R. A variable magnetic field of induction \[B={{B}_{0}}{{e}^{-t}}\]is established inside the coil. If the key (K) is closed, the electrical power developed right after closing the switch is equal to.
A)
\[\frac{B_{0}^{2}\pi {{r}^{2}}}{R}\] done
clear
B)
\[\frac{{{B}_{0}}10{{r}^{3}}}{R}\] done
clear
C)
\[\frac{B_{0}^{2}{{\pi }^{2}}{{r}^{4}}R}{5}\] done
clear
D)
\[\frac{B_{0}^{2}{{\pi }^{2}}{{r}^{4}}}{R}\] done
clear
View Solution play_arrow
question_answer 7)
A conductor AB of length\[l\]moves in x - y plane with velocity \[\vec{v}={{v}_{0}}(\hat{i}-\hat{j})\]. A magnetic field \[\overset{\to }{\mathop{B}}\,={{B}_{0}}(\hat{i}+\hat{j})\] exists in the region. The iduced Emf is
A)
zero done
clear
B)
\[{{B}_{0}}l{{v}_{0}}\] done
clear
C)
\[{{B}_{0}}l{{v}_{0}}\] done
clear
D)
\[\sqrt{2}{{B}_{0}}1{{v}_{0}}\] done
clear
View Solution play_arrow
question_answer 8)
A current carrying infinitely long wire is kept along the diameter of a circular wire loop, without touching it, the correct statement(s) is(are) I. The emf induced in the loop is zero if the current is constant. II. The emf induced in the loop is finite if the current is constant. III. The emf induced in the loop is zero if the current decreases at a steady rate.
A)
I only done
clear
B)
II only done
clear
C)
I and II done
clear
D)
I, II and III done
clear
View Solution play_arrow
question_answer 9)
Two different wire loops are concentric and lie in the same plane. The current in the outer loop (I) is clockwise and increases with time. The induced current in the inner loop
A)
is clockwise done
clear
B)
is zero done
clear
C)
is counter clockwise done
clear
D)
has a direction that depends on the ratio of the loop radii. done
clear
View Solution play_arrow
question_answer 10)
Fig shown below represents an area \[A=0.5\,{{m}^{2}}\] situated in a uniform magnetic field \[B=2.0\,weber/{{m}^{2}}\] and making an angle of \[60{}^\circ \] with respect to magnetic field.
The value of the magnetic flux through the area would be equal to
A)
2.0 weber done
clear
B)
\[\sqrt{3}\text{ }weber~~~\] done
clear
C)
\[\sqrt{3}\text{/2 }weber\] done
clear
D)
0.5 weber done
clear
View Solution play_arrow
question_answer 11)
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 done
clear
B)
39 m V; left to right done
clear
C)
31 m V; right to left done
clear
D)
31 m V; left to right done
clear
View Solution play_arrow
question_answer 12)
Magnetic flux linked with a stationary loop of resistance R varies with respect to time during the time period T as follows: \[\phi =at(T-t)\] The amount of heat generated in the loop during that time (inductance of the coil is negligible) is
A)
\[\frac{aT}{3R}\] done
clear
B)
\[\frac{{{a}^{2}}{{T}^{2}}}{3R}\] done
clear
C)
\[\frac{{{a}^{2}}{{T}^{2}}}{R}\] done
clear
D)
\[\frac{{{a}^{2}}{{T}^{3}}}{3R}\] done
clear
View Solution play_arrow
question_answer 13)
A conducting circular loop is placed in a uniform magnetic field of 0.04 T with its plane perpendicular to the magnetic field. The radius of the loop starts shrinking at 2 mm/s. The induced emf in the loop when the radius is 2 cm is
A)
\[4.8\pi \mu \,V\] done
clear
B)
\[0.8\pi \mu \,V\] done
clear
C)
\[1.6\pi \mu \,V\] done
clear
D)
\[3.2\pi \mu \,V\] done
clear
View Solution play_arrow
question_answer 14)
In a uniform and constant magnetic field of induction B, two long conducting wires ab and cd are kept parallel to each other at distance \[\ell \] with their plane perpendicular to B. The ends a and c are connected together by an ideal inductor of inductance L. A conducting slider wire PQ is imparted a speed \[{{v}_{0}}\] at time t=0. The situation is shown in the figure. At time\[t=\frac{\pi \sqrt{ML}}{4\,B\ell }\], the value of current \[I\] through the wire PQ is (ignore any resistance, electrical as well as mechanical)
A)
\[\sqrt{\frac{mv_{0}^{2}}{L}}\] done
clear
B)
\[\sqrt{\frac{mv_{0}^{2}}{2L}}\] done
clear
C)
\[\sqrt{\frac{mv_{0}^{2}}{4L}}\] done
clear
D)
zero done
clear
View Solution play_arrow
question_answer 15)
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 done
clear
B)
1.5A done
clear
C)
0.26A done
clear
D)
0.10A done
clear
View Solution play_arrow
question_answer 16)
A square loop with 2.0 m sides is perpendicular to a uniform magnetic field, with half the area of the loop in the field is shown in figure. The loop contains a 20.0 V battery with negligible internal resistance. If the magnitude of the field varies with time according to B = 0.042-0.871, with B in tesia and t in second. The net emf of the circuit is:
A)
\[20.0\,V\] done
clear
B)
\[18.26\,V\] done
clear
C)
\[21.74\,V\] done
clear
D)
None of these done
clear
View Solution play_arrow
question_answer 17)
A coil of circular cross-section having 1000 turns and\[4\,c{{m}^{2}}\] face area is placed with its axis parallel to a magnetic field which decreases by\[{{10}^{-2}}\,Wb\,\,{{m}^{-2}}\] in 0.01 s. The e.m.f. induced in the coil is:
A)
400mV done
clear
B)
200mV done
clear
C)
4mV done
clear
D)
0.4mV done
clear
View Solution play_arrow
question_answer 18)
The radius of the circular conducting loop shown in fig. is R. Magnetic field is decreasing at a constant rate a. Resistance per unit length of the loop is \[\rho \].
Then, the current in wire AB is (AB is one of the diameters)
A)
\[\frac{R\alpha }{2\rho }\]from A to B done
clear
B)
\[\frac{R\alpha }{2\rho }\] from B to A done
clear
C)
\[\frac{R\alpha }{2\rho }\] from A to B done
clear
D)
0 done
clear
View Solution play_arrow
question_answer 19)
An equilateral triangular loop ABC made of uniform thin wires is being pulled out of a region with a uniform speed v, where a uniform magnetic field \[\vec{B}\] perpendicular to the plane of the loop exists. At time t=0, the point A is at the edge of the magnetic field. The induced current (I) vs time (t) graph will be as
A)
B)
C)
D)
View Solution play_arrow
question_answer 20)
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 done
clear
B)
\[\frac{2Brv}{R}\] done
clear
C)
\[\frac{4Brv}{R}\] done
clear
D)
\[\frac{8Brv}{R}\] done
clear
View Solution play_arrow
question_answer 21)
A flexible wire loop in the shape of a circle has radius that grown linearly with time. There is a magnetic field perpendicular to the plane of the loop that has a magnitude inversely proportional to the distance from the center of the loop, \[B(r)\propto \frac{1}{r}\].How does the emf E vary with time?
A)
\[E\propto {{t}^{2}}\] done
clear
B)
\[E\propto t\] done
clear
C)
\[E\propto \sqrt{t}\] done
clear
D)
E is constant done
clear
View Solution play_arrow
question_answer 22)
Charge Q is uniformly distributed on a thin insulating ring of mass m which is initially at rest. To what angular velocity will the ring be accelerated when a magnetic field B, perpendicular to the plane of the ring, is switched on?
A)
\[\frac{QB}{2m}\] done
clear
B)
\[\frac{3QB}{2m}\] done
clear
C)
\[\frac{QB}{m}\] done
clear
D)
\[\frac{QB}{4m}\] done
clear
View Solution play_arrow
question_answer 23)
A rectangular coil has a long straight wire passing through its centroid perpendicular to its plane as shown. If current through the wire varies as \[i={{i}_{0}}\sin \omega t\], induced current in the coil will be (Given R = Resistance of the coil)
A)
\[\frac{{{i}_{0}}\sin \omega t}{R}\] done
clear
B)
\[\frac{\pi a\sin \omega t}{bR}\] done
clear
C)
zero done
clear
D)
\[\frac{\pi a\cos \omega t}{bR}\] done
clear
View Solution play_arrow
question_answer 24)
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 done
clear
B)
four times in the first wheel than in the second wheel done
clear
C)
will be double in the second wheel than that of the first wheel done
clear
D)
will be equal in both these wheels done
clear
View Solution play_arrow
question_answer 25)
The magnetic field in a region is given by \[B={{B}_{0}}\left( 1+\frac{x}{a} \right)\hat{k}\]. A square loop of edge-length d is placed with its edges along the x and y-axes. The loop is moved with a constant velocity\[v={{v}_{0}}\hat{i}.\]The emf induced in the loop is:
A)
zero done
clear
B)
\[{{v}_{0}}{{B}_{0}}d\] done
clear
C)
\[\frac{{{v}_{0}}{{B}_{0}}{{d}^{3}}}{{{a}^{2}}}\] done
clear
D)
\[\frac{{{v}_{0}}{{B}_{0}}{{d}^{2}}}{a}\] done
clear
View Solution play_arrow
question_answer 26)
A sliding wire of length 0.25 m and having a resistance of \[0.5\Omega \] moves along conducting guiding rails AB and CD with a uniform speed of 4 m/s. A magnetic field of 0.5 T exists normal to the plane of ABCD directed into the page. The guides are short -circuited with resistances of 4 and \[2\,\Omega \] as shown. The current through the sliding wire is:
A)
0.27 A done
clear
B)
0.37 A done
clear
C)
1.0 A done
clear
D)
0.72A done
clear
View Solution play_arrow
question_answer 27)
An L-shaped conductor rod is moving in transverse magnetic field as shown in the figure. Potential difference between ends of the rod is maximum if the rod is moving with velocity
A)
\[4\hat{i}-6\hat{j}\,m/s\] done
clear
B)
\[-\,4\hat{i}+6\hat{j}\,m/s\] done
clear
C)
\[3\hat{i}+2\hat{j}\,m/s\] done
clear
D)
\[\sqrt{13}\hat{i}\,m/s\] done
clear
View Solution play_arrow
question_answer 28)
A conducting rod of mass m and \[\ell \]is placed on a smooth horizontal surface in a region where transverse uniform magnetic field B exists in the region. At t=0, constant force .F starts acting on the rod at its mid-point as shown. Potential difference between ends of the rod, \[{{V}_{p}}-{{V}_{Q}}\] at any time t is
A)
\[\frac{BF\ell t}{2m}\] done
clear
B)
\[\frac{BF\ell t}{4m}\] done
clear
C)
\[\frac{5BF\ell t}{8m}\] done
clear
D)
\[\frac{7BF\ell t}{8m}\] done
clear
View Solution play_arrow
question_answer 29)
A thin circular ring of area A is perpendicular to uniform magnetic field of induction B. A small cut is made in the ring and a galvanometer is connected across the ends such that the total resistance of circuit is R. When the ring is suddenly squeezed to zero area, the charge flowing through the galvanometer is
A)
\[\frac{BR}{A}\] done
clear
B)
\[\frac{AB}{R}\] done
clear
C)
ABR done
clear
D)
\[{{B}^{2}}\,A/{{R}^{2}}\] done
clear
View Solution play_arrow
question_answer 30)
A 0.1 m long conductor carrying a current of 50 I A is perpendicular to a magnetic field of 1.21 mT. The mechanical power to move the conductor 1 with a speed of \[1\,m{{s}^{-1}}\] is
A)
0.25 m W done
clear
B)
6.25 m W done
clear
C)
0.625 W done
clear
D)
1W done
clear
View Solution play_arrow
question_answer 31)
A wire is bent to form the double loop shown in Fig. There is a uniform magnetic field directed into the plane of the loop. If the magnitude of this field is decreasing, the current will flow from
A)
a to b and c to d done
clear
B)
b to a and d to c done
clear
C)
a to b and d to c done
clear
D)
b to a and c to d done
clear
View Solution play_arrow
question_answer 32)
A conducting wire xy of length\[l\]and mass m is sliding without friction on vertical conduction rails ab and cd shown in Fig. A uniform magnetic field B exists perpendicular to the plane of the rails, x moves with a constant velocity of
A)
\[\frac{mgR}{Bl}\] done
clear
B)
\[\frac{mgR}{B{{l}^{2}}}\] done
clear
C)
\[\frac{mgR}{{{B}^{2}}{{l}^{2}}}\] done
clear
D)
\[\frac{mgR}{{{B}^{2}}l}\] done
clear
View Solution play_arrow
question_answer 33)
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)
\[\frac{9B\omega {{\ell }^{2}}}{2}\] done
clear
B)
\[\frac{4B\omega {{\ell }^{2}}}{2}\] done
clear
C)
\[\frac{5B\omega {{\ell }^{2}}}{2}\] done
clear
D)
\[\frac{B\omega {{\ell }^{2}}}{2}\] done
clear
View Solution play_arrow
question_answer 34)
A uniform magnetic field of induction B is confined to a cylindrical region of radius R. The magnetic field is increasing at a constant rate of \[\frac{dB}{dt}\] (tesla/second). An electron of charge q, placed at the point P on the periphery of the field experiences an acceleration.
A)
\[\frac{BR}{(\sqrt{2}+1)m}\] towards left done
clear
B)
\[\frac{1}{2}\,\frac{eR}{m}\,\frac{dB}{dt}\] towards left done
clear
C)
\[\frac{eR}{m}\frac{dB}{dt}\] towards left done
clear
D)
zero done
clear
View Solution play_arrow
question_answer 35)
An equilateral triangular loop having a resistance R and length of each side\[\ell \]is placed in magnetic field which is varying at \[\frac{dB}{dt}=1\,T/s\]. The induced current in the loop will be
A)
\[\frac{\sqrt{3}}{4}\frac{{{\ell }^{2}}}{R}\] done
clear
B)
\[\frac{4}{\sqrt{3}}\frac{{{\ell }^{2}}}{R}\] done
clear
C)
\[\frac{\sqrt{3}}{4}\,\frac{R}{{{\ell }^{2}}}\] done
clear
D)
\[\frac{4}{\sqrt{3}}\frac{R}{{{\ell }^{2}}}\] done
clear
View Solution play_arrow
question_answer 36)
A copper rod of length 0.19 m is moving parallel to a long wire with a uniform velocity of 10 m/s. The long wire carries 5 ampere current and is perpendicular to the rod. The ends of the rod are at distances 0.01 m and 0.2 m from the wire. The emf induced in the rod will be-
A)
\[10\,\mu V\] done
clear
B)
\[20\,\mu V\] done
clear
C)
\[30\,\mu V\] done
clear
D)
\[40\,\mu V\] done
clear
View Solution play_arrow
question_answer 37)
A metallic square loop ABCD is moving in its own plane with velocity v in a uniform magnetic field perpendicular to its plane as shown in the figure. An electric field is induced
A)
in AD, but not in BC done
clear
B)
in BC, but not in AD done
clear
C)
neither in AD nor in BC done
clear
D)
in both AD and BC done
clear
View Solution play_arrow
question_answer 38)
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)
\[\frac{mg\,R\,\sin \theta }{{{B}^{2}}{{l}^{2}}}\] done
clear
B)
\[\frac{mg\,R\,\sin \theta }{B{{l}^{2}}}\] done
clear
C)
\[\frac{mg\,R\,\sin \theta }{{{B}^{2}}{{l}^{5}}}\] done
clear
D)
\[\frac{mg\,R\,\sin \theta }{B{{l}^{4}}}\] done
clear
View Solution play_arrow
question_answer 39)
A plane loop, shaped as two squares of sides a =1 m and b=0.4 m is introduced into a uniform magnetic field\[\bot \]to the plane of loop. The magnetic field varies as \[B={{10}^{-3}}\sin \](100t) T. The amplitude of the current induced in the loop if its resistance per unit length is\[r=5\,m{{\Omega }^{-1}}\]is
A)
2 A done
clear
B)
3 A done
clear
C)
4 A done
clear
D)
5 A done
clear
View Solution play_arrow
question_answer 40)
PQ is an infinite current carrying conductor. AB and CD are smooth conducting rods on which a conductor EF moves with constant velocity v as shown. The force needed to maintain constant speed of EF is
A)
\[\frac{1}{vR}{{\left[ \frac{{{\mu }_{0}}Iv}{2\pi }In\,\left( \frac{b}{a} \right) \right]}^{2}}\] done
clear
B)
\[{{\left[ \frac{{{\mu }_{0}}Iv}{2\pi }In\left( \frac{a}{b} \right) \right]}^{2}}\frac{1}{vR}\] done
clear
C)
\[{{\left[ \frac{{{\mu }_{0}}Iv}{2\pi }In\left( \frac{b}{a} \right) \right]}^{2}}\frac{v}{R}\] done
clear
D)
\[\frac{v}{R}{{\left[ \frac{{{\mu }_{0}}Iv}{2\pi }In\left( \frac{a}{b} \right) \right]}^{2}}\] done
clear
View Solution play_arrow
question_answer 41)
A coil of resistance 400Q is placed in a magnetic field. If the magnetic flux \[\phi \] (wb) linked with the coil varies with time t (sec) as\[\phi =50{{t}^{2}}+4\]. The current in the coil at t=2 sec is:
A)
0.5 A done
clear
B)
0.1 A done
clear
C)
2 A done
clear
D)
1 A done
clear
View Solution play_arrow
question_answer 42)
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 done
clear
B)
\[1.5\times {{10}^{-6}}\,A\]clockwise done
clear
C)
\[0.75\times {{10}^{-6}}\,A\] anticlockwise done
clear
D)
\[0.75\times {{10}^{-6}}\,A\]clockwise done
clear
View Solution play_arrow
question_answer 43)
A rectangular coil of 20 turns and area of cross- section 25 sq. cm has a resistance of\[100\,\Omega \]. If a magnetic field which is perpendicular to the plane of coil changes at a rate of 1000 tesla per second, the current in the coil is
A)
1 A done
clear
B)
50 A done
clear
C)
0.5 A done
clear
D)
5 A done
clear
View Solution play_arrow
question_answer 44)
A rectangular loop PQRS, is pulled with constant speed into a uniform transverse magnetic field by a force F (as shown). E.m.f. induced in side PS and potential difference between points P and S respectively are (Resistance of the loop = r)
A)
zero, \[\frac{Fr}{B\ell }\] done
clear
B)
zero, zero done
clear
C)
zero, \[\frac{Fr}{6B\ell }\] done
clear
D)
\[\frac{Fr}{6B\ell },\,\frac{Fr}{6B\ell }\] done
clear
View Solution play_arrow
question_answer 45)
A horizontal ring of radius \[r=\frac{1}{2}m\] is kept in a vertical constant magnetic field 1 T. The ring is collapsed from maximum area to zero area in 1 s. Then the emf induced in the ring is
A)
1 V done
clear
B)
\[(\pi /4)V\] done
clear
C)
\[(\pi /2)V\] done
clear
D)
\[\pi \,V\] done
clear
View Solution play_arrow
question_answer 46)
A conducting rod of length l is hinged at point O. It is free to rotate in vertical plane. There exists a uniform magnetic field \[\vec{B}\]in horizontal direction. The rod is released from position shown in the figure. When rod makes an angle \[\theta \] from released position then potential difference between two ends of the rod is proportional to:
A)
\[{{l}^{1/2}}\] done
clear
B)
The lower end will be at a lower potential done
clear
C)
\[\sin \theta \] done
clear
D)
\[{{\left( \sin \theta \right)}^{1/2}}\] done
clear
View Solution play_arrow
question_answer 47)
An aluminium ring hangs vertically from a thread with its axis pointing east - west. A coil is fixed near to the ring and coaxial with it. What is the initial motion of the aluminium ring when the current in the coil is switched on?
A)
moves toward E done
clear
B)
moves toward W done
clear
C)
moves toward N done
clear
D)
moves toward S done
clear
View Solution play_arrow
question_answer 48)
A resistance less ring has 2 bulbs A and B rated at 2V, 19 W and 2V, 29 W respectively. The ring encloses an ideal solenoid whose magnetic field is as shown. The radius of solenoid is 1 m and the number of turns/length =1000/m. The current changes at rate of 9 A/sec Find the value of P if power dissipated in bulb B is \[180{}^\circ \] watt.
A)
4 done
clear
B)
6 done
clear
C)
8 done
clear
D)
11 done
clear
View Solution play_arrow
question_answer 49)
A cylindrical region of radius 1 m has instantaneous homogenous magnetic field of 5T and it is increasing at a rate of 2T/s. A regular hexagonal loop ABCDEFA of side 1 m is being drawn in to the region with a constant speed of 1 m/s as shown in the figure. What is the magnitude of emf developed in the loop just after the shown instant when the corner A of the hexagon is coinciding with the centre of the circle?
A)
\[5/\sqrt{3}V\] done
clear
B)
\[2\pi /\sqrt{3}V\] done
clear
C)
\[(5\sqrt{3}+2\pi /3)\,V\] done
clear
D)
\[(5\sqrt{3}+\pi )\,V\] done
clear
View Solution play_arrow
question_answer 50)
A thin semicircular conducting ring (PQR) of radius 'r' is falling with its plane vertical in a horizontal magnetic field B, as shown in figure. The potential difference developed across thering when its speed is v, is:
A)
Zero done
clear
B)
\[Bv\pi {{r}^{2}}/2\] and P is at higher potential done
clear
C)
\[\pi rBv\] and R is at higher potential done
clear
D)
2rBv and R is at higher potential done
clear
View Solution play_arrow
question_answer 51)
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)
\[\frac{1}{{{(2x-a)}^{2}}}\] done
clear
B)
\[\frac{1}{{{(2x+a)}^{2}}}\] done
clear
C)
\[\frac{1}{(2x-a)(2x+a)}\] done
clear
D)
\[\frac{1}{{{x}^{2}}}\] done
clear
View Solution play_arrow
question_answer 52)
The approximate formula expressing the formula of mutual inductance of two thin coaxial loops of the same radius a when their centers are separated by a distance \[l\] with \[l\] >>a is
A)
\[\frac{1}{2}\,\frac{{{\mu }_{0}}\pi {{a}^{4}}}{{{l}^{3}}}\] done
clear
B)
\[\frac{1}{2}\,\frac{{{\mu }_{0}}\pi {{a}^{4}}}{{{l}^{2}}}\] done
clear
C)
\[\frac{{{\mu }_{0}}}{4\pi }\frac{\pi {{a}^{4}}}{{{l}^{2}}}\] done
clear
D)
\[\frac{{{\mu }_{0}}}{\pi }\frac{{{a}^{4}}}{{{l}^{3}}}\] done
clear
View Solution play_arrow
question_answer 53)
A bar magnet was pulled away from a hollow coil A as shown in fig. As the South Pole came out of the coil, the bar magnet next to hollow coil B experienced a magnetic force
A)
to the right done
clear
B)
to the left done
clear
C)
upward done
clear
D)
equal to zero done
clear
View Solution play_arrow
question_answer 54)
A superconducting loop of radius R has self-inductance L. A uniform and constant magnetic field B is applied perpendicular to the plane of the loop. Initially current in this loop is zero. The loop is rotated by \[180{}^\circ \]. The current in the loop after rotation is equal to
A)
zero done
clear
B)
\[\frac{B\pi {{R}^{2}}}{L}\] done
clear
C)
\[\frac{2B\pi {{R}^{2}}}{L}\] done
clear
D)
\[\frac{B\pi {{R}^{2}}}{2L}\] done
clear
View Solution play_arrow
question_answer 55)
Two inductances \[{{L}_{1}}\] and \[{{L}_{2}}\]are placed closer and in parallel. Their combined inductance is
A)
\[\frac{{{L}_{1}}{{L}_{2}}}{{{L}_{1}}+{{L}_{2}}}\] done
clear
B)
\[({{L}_{1}}+{{L}_{2}})\] done
clear
C)
\[({{L}_{1}}+{{L}_{2}})\,\frac{{{L}_{1}}}{{{L}_{2}}}\] done
clear
D)
\[({{L}_{1}}+{{L}_{2}})\,\frac{{{L}_{2}}}{{{L}_{1}}}\] done
clear
View Solution play_arrow
question_answer 56)
Two coils are at fixed locations. Which coil 1 has no current and the current in coil 2 increases at the rate of \[15.0\,A\,{{s}^{-1}}\], the emf in coil 1 is 25 mV, when coil 2 has no current and coil 1 has a current of 3.6 A, the flux linkage on coil 2 is
A)
16 m Wb done
clear
B)
10 m Wb done
clear
C)
4.00 m Wb done
clear
D)
6.00 m Wb done
clear
View Solution play_arrow
question_answer 57)
What is the self-inductance of a coil which produces 5V when the current changes from 3 ampere to 2 ampere in one millisecond?
A)
5000 henry done
clear
B)
5 milli-henry done
clear
C)
50 henry done
clear
D)
5 henry done
clear
View Solution play_arrow
question_answer 58)
Figure shows a rectangular coil near a long wire. The mutual inductance of the combination is
A)
\[\frac{{{\mu }_{0}}a}{2\pi }ln\left( 1-\frac{b}{c} \right)\] done
clear
B)
\[\frac{{{\mu }_{0}}a}{2\pi }ln\left( 1+\frac{b}{c} \right)\] done
clear
C)
\[\frac{{{\mu }_{0}}a}{\pi }ln\left( 1+\frac{b}{c} \right)\] done
clear
D)
\[\frac{{{\mu }_{0}}a}{\sqrt{2}\pi }ln\left( 1+\frac{b}{c} \right)\] done
clear
View Solution play_arrow
question_answer 59)
In an inductor of self-inductance L=2mH, current changes with time according to relation \[i={{t}^{2}}{{e}^{-t}}\]. At what time emf is zero?
A)
4s done
clear
B)
3s done
clear
C)
2s done
clear
D)
Is done
clear
View Solution play_arrow
question_answer 60)
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 done
clear
B)
6 H done
clear
C)
11 H done
clear
D)
12 H done
clear
View Solution play_arrow
question_answer 61)
A current of 1.5 A flows through a solenoid of length 20.0 cm, cross-section \[20.0\text{ }c{{m}^{2}}\] and 400 turns. The current is suddenly switched off in a short time of 1.0 millisecond. Ignoring the variation in the magnetic field the ends, the average back emf induced in the solenoid is:
A)
0.3 V done
clear
B)
9.6 V done
clear
C)
30.0 V done
clear
D)
3.0 V done
clear
View Solution play_arrow
question_answer 62)
Two circular coils can be arranged in any of the three situations shown in the figure. Their mutual inductance will be
A)
maximum in situation [a] done
clear
B)
maximum in situation [b] done
clear
C)
maximum in situation [c] done
clear
D)
the same in all situations done
clear
View Solution play_arrow
question_answer 63)
A small square loop of wire of side \[\ell \] is placed inside a large square loop of wire of side \[L(L>\ell )\].The loop are coplanar and their centre coincide. The mutual inductance of the system is proportional to
A)
\[\ell /L\] done
clear
B)
\[{{\ell }^{2}}/L\] done
clear
C)
\[L/\ell \] done
clear
D)
\[{{L}^{2}}/\ell \] done
clear
View Solution play_arrow
question_answer 64)
Two coils, one primary of 500 turns and one secondary of 25 turns, are wound on an iron ring of mean diameter 20 cm and cross-sectional area\[12\,c{{m}^{2}}\]. If the permeability of iron is 800, the mutual inductance is:
A)
0.48 H done
clear
B)
2.4 H done
clear
C)
0.12 H done
clear
D)
0.24 H done
clear
View Solution play_arrow
question_answer 65)
When the current in a certain inductor coil is 5.0 A and is increasing at the rate of 10.0 A/s, the potential difference across the coil is 140V. When the current is 5.0 A and decreasing at the rate of 10.0 A/s, the potential difference is 60V. The self-inductance of the coil is -
A)
2H done
clear
B)
4H done
clear
C)
8H done
clear
D)
12H done
clear
View Solution play_arrow
question_answer 66)
A wire of fixed lengths is wound on a solenoid of length \[\ell \] and radius r. Its self-inductance is found to be L. Now if same wire is wound on a solenoid of length \[\ell /2\] and radius r/2, then the self in- ductance will be -
A)
2L done
clear
B)
L done
clear
C)
4L done
clear
D)
8L done
clear
View Solution play_arrow
question_answer 67)
A rectangular loop has a sliding connector PQ of length \[\ell \] and resistance \[R\,\Omega \] and it is moving with a speed v as shown. The set-up is placed in a uniform magnetic field going m to the plane of the paper. The three currents \[{{I}_{1}},\,{{I}_{2}}\] and / are
A)
\[{{I}_{1}}=-{{I}_{2}}=\frac{Blv}{6R},\,I=\frac{2Blv}{6R}\] done
clear
B)
\[{{I}_{1}}={{I}_{2}}=\frac{Blv}{3R},\,I=\frac{2Blv}{3R}\] done
clear
C)
\[{{I}_{1}}={{I}_{2}}=I=\frac{Blv}{R}\] done
clear
D)
\[{{I}_{1}}={{I}_{2}}=\frac{Blv}{6R}\], \[I=\frac{Blv}{3R}\] done
clear
View Solution play_arrow
question_answer 68)
A boat is moving due east in a region where the earth's magnetic field is \[5.0\times {{10}^{-5}}N{{A}^{-1}}\,{{m}^{-1}}\] due north and horizontal. The boat carries a vertical aerial 2 m long. If the speed of the boat is\[1.50\,m{{s}^{-1}}\], the magnitude of the induced emf in the wire of aerial is
A)
0.75 mV done
clear
B)
0.50 mV done
clear
C)
0.15 mV done
clear
D)
1 mV done
clear
View Solution play_arrow
question_answer 69)
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 done
clear
B)
4.5 mV done
clear
C)
1.5mV done
clear
D)
6.0 mV done
clear
View Solution play_arrow
question_answer 70)
A coil is suspended in a uniform magnetic field, with the plane of the coil parallel to the magnetic lines of force. When a current is passed through the coil it starts oscillating; It is very difficult to stop. But if an aluminium plate is placed near to the coil, it stops. This is due to:
A)
developement of air current when the plate is placed done
clear
B)
induction of electrical charge on the plate done
clear
C)
shielding of magnetic lines of force as aluminium is a paramagnetic material. done
clear
D)
electromagnetic induction in the aluminium plate giving rise to electromagnetic damping. done
clear
View Solution play_arrow
question_answer 71)
A long solenoid has 500 turns. When a current of 2 ampere is passed through it, the resulting magnetic flux linked with each turn of the solenoid is \[4\times {{10}^{-3}}\,Wb\]. The self- inductance of the solenoid is
A)
2.5 henry done
clear
B)
2.0 henry done
clear
C)
1.0 henry done
clear
D)
40 henry done
clear
View Solution play_arrow
question_answer 72)
A circular coil is radius 5 cm has 500 turns of a wire. The approximate value of the coefficient of self-induction of the coil will be-
A)
\[25\text{ }mH\] done
clear
B)
\[25\times {{10}^{-3}}\,mH\] done
clear
C)
\[50\times {{10}^{-3}}\,mH\] done
clear
D)
\[50\times {{10}^{-3}}\,H\] done
clear
View Solution play_arrow
question_answer 73)
A uniform coil of self-inductance \[1.8\times {{10}^{-4}}\,H\] and resistance 6W is broken up into two identical coils. These two coils are then connected in parallel across a 12 V battery. The circuit time constant and steady state current through the battery respectively are:
A)
\[30\text{ }\mu s,\text{ }8\text{ }A\] done
clear
B)
30ms, 8mA done
clear
C)
30s, 8 A done
clear
D)
300s, 800 A done
clear
View Solution play_arrow
question_answer 74)
The back e.m.f. in a d.c. motor is maximum, when
A)
the motor has picked up max speed done
clear
B)
the motor has just started moving done
clear
C)
the speed of motor is still on the increase done
clear
D)
the motor has just been switched off done
clear
View Solution play_arrow
question_answer 75)
A motor having an armature of resistance \[2\Omega \]. Is designed to operate at 220 V mains. At full speed, it develops a back emf of 210V. When the motor is running at full speed, the current in the armature is:
A)
3 A done
clear
B)
5 A done
clear
C)
7A done
clear
D)
10A done
clear
View Solution play_arrow
question_answer 76)
A simple electric motor has an armature resistance of \[1\Omega ~\] and runs from a dc source of 12 volt. When running unloaded it draws a current of 2 amp. When a certain load is connected, its speed becomes one-half of its unloaded value. What is the new value of current drawn?
A)
7 A done
clear
B)
3 A done
clear
C)
5 A done
clear
D)
4 A done
clear
View Solution play_arrow
question_answer 77)
When a metallic plate swings between the poles of a magnet
A)
no effect on the plate done
clear
B)
eddy currents are set up inside the plate and the direction of the current is along the motion of the plate done
clear
C)
eddy currents are set up inside the plate and the direction of the current opposes the motion of the plate done
clear
D)
eddy currents are set up inside the plate done
clear
View Solution play_arrow
question_answer 78)
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 done
clear
B)
Q done
clear
C)
L done
clear
D)
M done
clear
View Solution play_arrow
question_answer 79)
A rectangular coil of 200 turns of wire \[15\times 40\,c{{m}^{2}}\] makes 50 r.p.s. about an axis in its plane parallel to its longer side and perpendicular to a magnetic field of intensity \[0.08\,Wb/{{m}^{2}}\]. what is the instantaneous value of induced e.m.f. when the plane of the coil makes an angle with magnetic field of \[45{}^\circ \].
A)
213.3 V done
clear
B)
301.7 V done
clear
C)
151.5 V done
clear
D)
zero done
clear
View Solution play_arrow
question_answer 80)
A generator has an e.m.f. of 440 Volt and internal resistance of 4000 hm. Its terminals are connected to a load of 4000 ohm. The voltage across the load is
A)
220 volt done
clear
B)
440 volt done
clear
C)
200 volt done
clear
D)
400 volt done
clear
View Solution play_arrow
question_answer 81)
A metallic rod of length T is tied to a string of length U and made to rotate with angular speed co on a horizontal table with one end of the string fixed. If there is a vertical magnetic field 'B' in the region, the e.m.f. induced across the ends of the rod is
A)
\[\frac{2B\omega {{\ell }^{2}}}{2}\] done
clear
B)
\[\frac{3B\omega {{\ell }^{2}}}{2}\] done
clear
C)
\[\frac{4B\omega {{\ell }^{2}}}{2}\] done
clear
D)
\[\frac{5B\omega {{\ell }^{2}}}{2}\] done
clear
View Solution play_arrow
question_answer 82)
A circular loop of radius 0.3 cm lies parallel to a much bigger circular loop of radius 20 cm. The centre of the small loop is on the axis of the bigger loop. The distance between their centres is 15 cm. If a current of 2.0 A flows through the smaller loop, then the flux linked with bigger loop is
A)
\[9.1\times {{10}^{-11}}\,weber\] done
clear
B)
\[6\times {{10}^{-11}}\,weber\] done
clear
C)
\[3.3\times {{10}^{-11}}\,weber\] done
clear
D)
\[6.6\times {{10}^{-9}}\,weber\] done
clear
View Solution play_arrow
question_answer 83)
In a coil of resistance 100 Q, a current is induced by changing the magnetic flux through it as shown in the figure. The magnitude of change in flux through the coil is
A)
250 Wb done
clear
B)
275 Wb done
clear
C)
200 Wb done
clear
D)
225 Wb done
clear
View Solution play_arrow
question_answer 84)
A charge Q is uniformly distributed over the surface of non-conducting disc of radius R. The disc rotates about an axis perpendicular to its plane and passing through its centre with an angular velocity co. As a result of this rotation a magnetic field of induction B is obtained at the centre of the disc. If we keep both the amount of charge placed on the disc and its angular velocity to be constant and vary the radius of the disc then the variation of the magnetic induction at the centre of the disc will be represented by the figure:
A)
B)
C)
D)
View Solution play_arrow
question_answer 85)
The two rails of a railway track, insulated from each other and the ground, are connected to a milli voltmeter. What is the reading of the milli voltmeter when a train travels at a speed of 180 km/hour along the track, given that the vertical component of earth's magnetic field is\[0.2\times {{10}^{-4}}\,weber/{{m}^{2}}\] and the rails are separated by 1 m?
A)
1 done
clear
B)
3 done
clear
C)
5 done
clear
D)
7 done
clear
View Solution play_arrow
question_answer 86)
A square metal wire loop of side 10 cm and resistance 1 ohm is moved with a constant velocity \[{{v}_{0}}\] in a uniform magnetic field of induction \[B=2\,weber/{{m}^{2}}\] as shown in the figure. The magnetic field lines are perpendicular to the plane of the loop (directed into the paper). The loop is connected to a network of resistors each of value 3 ohms. The resistances of the lead wires OS and PQ are negligible. What should be the speed of the loop so as to have a steady current of 1 milliampere in the loop? Give the direction of current in the loop.
A)
2.3 m/s done
clear
B)
1.2 m/s done
clear
C)
0.3 m/s done
clear
D)
0.02 m/s done
clear
View Solution play_arrow
question_answer 87)
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)
\[\frac{Bvr}{2}\] done
clear
B)
\[\frac{3Bvr}{2}\] done
clear
C)
\[\frac{Bvr}{2}\] done
clear
D)
\[\frac{-3Bvr}{2}\] done
clear
View Solution play_arrow
question_answer 88)
The figure below depicts a circular loop of radius R carrying a fixed current I. The upper half of the loop is placed in a uniform magnetic field of magnitude B, perpendicular to the plane of the paper, as shown. The magnitude of the force on the loop is (neglect gravity)
A)
BIR done
clear
B)
2BIR done
clear
C)
\[\pi BIR\] done
clear
D)
\[2\pi BIR\] done
clear
View Solution play_arrow
question_answer 89)
Two identical circular current carrying coils 1 and 2, each of radius R are placed adjacently a distance d apart (d<<R). They carry equal currents/in opposite sense. Let \[{{L}_{1}},\,{{L}_{2}},\,{{M}_{12}}\] and\[{{M}_{21}}\] denote the self and mutual inductances. Which of the following is at least approximately true?
A)
\[\left| \left. {{L}_{1}} \right| \right.=\left| \left. {{M}_{21}} \right| \right.\] done
clear
B)
\[{{M}_{21}}>{{L}_{1}}\] done
clear
C)
\[{{L}_{1}}=-{{L}_{2}}\] done
clear
D)
\[{{M}_{12}}=-{{M}_{21}}\] done
clear
View Solution play_arrow
question_answer 90)
An infinitesimally small bar magnet of dipole moment \[\vec{M}\] is pointing and moving with the speed v in the \[\hat{x}\]- direction. A small closed circular conducting loop of radius a and negligible self- inductance lies in the y-z plane with its center at x = 0, and its axis coinciding with the x-axis. Find the force opposing the motion of the magnet, if the resistance of the loop is R. Assume that the distance x of the magnet from the center of the loop is much greater than a.
A)
\[\frac{21}{4}\frac{\mu _{0}^{2}{{M}^{2}}{{a}^{4}}v}{R{{x}^{8}}}\] done
clear
B)
\[\frac{16}{3}\frac{{{\mu }_{0}}{{M}^{2}}{{a}^{2}}{{v}^{2}}}{R{{x}^{3}}}\] done
clear
C)
\[\frac{3}{23}\frac{{{\mu }_{0}}Ma{{v}^{2}}}{R{{x}^{3}}}\] done
clear
D)
None of these done
clear
View Solution play_arrow
question_answer 91)
ABCD is a wire frame in the shape of an isosceles trapezium (i.e., length AB = length CD) enter a magnetic field with flux density B at t=0 as shown in the figure. If the total resistance of wire frame is R. What is the value of the induced current in the wire frame after t seconds, assuming that the frame has to entered the field completely by then? [v=Velocity of frame]
A)
zero done
clear
B)
\[\frac{Bv}{R}(2vt\,\sin \,\theta +\ell )\] done
clear
C)
\[\frac{Bv}{R}\left( \frac{2vt\,}{\tan \,\theta }+\ell \right)\] done
clear
D)
\[\frac{B}{v}\] done
clear
View Solution play_arrow
question_answer 92)
The magnetic flux \[\phi \] linked with a conducting coil depends on time as \[\phi =4{{t}^{n}}+6\], where n is a positive constant. The induced emf in the coil is e. Then which is wrong?
A)
If \[0<n<1\], \[e\ne 0\] and \[\left. \left| e \right. \right|\]decreases with time done
clear
B)
If n=1, e is constant done
clear
C)
If n > 1, \[\left| e \right|\]increases with time done
clear
D)
If n>l, \[\left| e \right|\] decreases with time done
clear
View Solution play_arrow
question_answer 93)
A uniform circular loop of radius a and resistance R is placed perpendicular to a uniform magnetic field B. One half of the loop is rotated about the diameter with angular velocity\[\omega \]as shown in Fig. Then, the current in the loop is
A)
\[\frac{\pi {{a}^{2}}B\omega }{4R}\], when \[\theta \] is zero done
clear
B)
\[\frac{\pi {{a}^{2}}B\omega }{2R}\], when \[\theta \] is zero done
clear
C)
zero, when \[\theta =\pi /2\] done
clear
D)
\[\frac{\pi {{a}^{2}}B\omega }{2R}\], when \[\theta =\pi /2\] done
clear
View Solution play_arrow
question_answer 94)
A metal rod moves at a constant velocity in a direction perpendicular to its length. A constant, uniform magnetic field exists in space in a direction perpendicular to the rod as well as its velocity. Select the correct statement from the following.
A)
The entire rod is at the same electric potential. done
clear
B)
There is an electric field in the rod. done
clear
C)
The electric potential is highest at the centre of the rod and decreases towards its ends. done
clear
D)
The electric potential is lowest at the centre of the rod, and increases towards its ends done
clear
View Solution play_arrow
question_answer 95)
A nonconducting ring of mass m and radius R has a charge Q uniformly distributed over its circumference. The ring is placed on a rough horizontal surface such that the plane of the ring is parallel to the surface. A vertical magnetic field \[B={{B}_{0}}{{t}^{2}}\] tesla is switched on. After 2 second from switching on the magnetic field the ring is just about to rotate about vertical axis through its centre. Then
A)
the induced electric field is quadratic in time t done
clear
B)
the force tangential to the ring is\[9{{B}_{0}}QRt\] done
clear
C)
until 2 seconds, the friction force does not come into play done
clear
D)
the friction coefficient between the ring and the surface is \[\frac{2{{B}_{0}}RQ}{mg}\]. done
clear
View Solution play_arrow
question_answer 96)
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 done
clear
B)
magnitude of current in the loop is\[\frac{Bv}{\lambda (\sqrt{2}+1)}\] done
clear
C)
current in the loop is independent of time. done
clear
D)
magnitude of current decreases as time increases. done
clear
View Solution play_arrow
question_answer 97)
A (current versus time) graph of the current passing through a solenoid is shown in figure. If the back emf at t=3s is e, find the back emf at t = 7 s
A)
\[e/2\] done
clear
B)
0 done
clear
C)
\[\frac{-e}{2}\] done
clear
D)
\[-3e\] done
clear
View Solution play_arrow
question_answer 98)
The incorrect statements is/are
A)
The resistance offered by an inductor in a d. c circuit is always constant. done
clear
B)
The resistance of inductor in steady state is zero. done
clear
C)
An inductor is connected to a battery through a switch. The emf induced in the inductor is much larger when the switch is opened as compared to the emf induced when the switch is closed. done
clear
D)
To reduce the rate of increases of current through a solenoid should increase the time constant\[\left( \frac{L}{R} \right)\]. done
clear
View Solution play_arrow
question_answer 99)
In a conducting cycle wheel (of n spokes), each spoke of length fi is rotating with angular speed \[\omega \] in uniform perpendicular magnetic field B. If due to flux cutting each metal spoke behaves as an identical cell of emf(e) then net emf of the system is
A)
\[nB\omega {{l}^{2}}\] done
clear
B)
\[\frac{1}{2}nB\omega {{l}^{2}}\] done
clear
C)
\[\frac{1}{2}B\omega {{l}^{2}}\] done
clear
D)
\[B\omega {{l}^{2}}\] done
clear
View Solution play_arrow
question_answer 100)
A rod OA of length \[l\] is rotating (about end 0) over a conducting ring in crossed magnetic field B with constant angular velocity co as shown in figure
A)
Current flowing through the rod is\[\frac{B\omega \,{{l}^{2}}}{R}\] done
clear
B)
Magnetic force acting on the rod is \[\frac{3{{B}^{2}}\omega \,{{l}^{3}}}{4R}\] done
clear
C)
Torque due to magnetic force acting on the rod is\[\frac{3{{B}^{2}}\omega \,{{l}^{4}}}{8R}\] done
clear
D)
Magnitude of external force that acts perpendicularly at the end of the rod to maintain the constant angular speed is \[\frac{3{{B}^{2}}\omega \,{{l}^{3}}}{5R}\]. done
clear
View Solution play_arrow