IIT JEE Advanced & Mains Physics 2018 : Electricity : Rank file / expected questions : IX

IIT JEE Advanced & Mains Physics 2018 : Electricity : Rank file / expected questions / Physicsmynd Elite Series  /  Page  IX

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73 – 75 ] JEE Physics Previous

A point charge q moves from point P to point S along the path PQRS (Fig.) in a uniform electric filed E pointing parallel to the positive direction of the X-axis. The coordinates of points P,Q,R and S are (a,b,0), (2a,0,0) (a,-b,0) (0,0,0) respectively. Find work done by the field in the above process is .

74 ]  A rigid insulated wire frame in the form of a right angled triangle ABC, is set in a vertical plane as shown in figure. Two beads of equal masses m each and carrying charges {q}_{1} and {q}_{2} are connected by a cord of length I and can slide without friction on the wires.

Considering the case when the beads are stationary determine
[ A ]  (i) The angle \alpha
          (ii) The tension in the cord
         (iii) The normal reaction on the beads
[ B ] If the cord is now cut what are the value of the charges for which the beads continue to remain stationary?

75 ] Two capacitors A and B with capacitors 3\mu{F} and 2\mu{F} are charged to a potential difference of 100 V and 180 V respectively. The plates of the capacitors are connected as shown in the figure with one wire of each capacitor free. The upper plate of A is positive and that of B is negative. An uncharged 2\mu{F} capacitor C with lead wires falls on the free ends to complete the circuit. Calculate :

[ A ] the final charge on the three capacitors and
[ B ] the amount of electrostatic energy stored in the system before and after completion of the circuit.

76 ] Three concentric metallic spherical shells of radii R, 2R, 3R, are given charges {Q}_{1},{Q}_{2},{Q}_{3}, respectively. It is found that the surface charge densities on the outer surfaces of the shells are equal. Then, the ratio of the charges given to the shells, {Q}_{1}:{Q}_{2}:{Q}_{3}, is

A ]  1:2:3
B ]  1:3:5
C ]  1:4:9
D ] 1:8:18

77 ] Two copper balls, each weighting 10 g are kept in air 10 cm apart. If one electron from every {10}^{6} atoms is transferred from one ball to the other, the coulomb force between them is (atomic weight of copper is 63.5)

A ]  {2.0}\times{10}^{10}N
B ]  {2.0}\times{10}^{4}N
C ]  {2.0}\times{10}^{8}N
D ]  {2.0}\times{10}^{6}N

78 – 79 ] Consider four equal charges Q  placed at the four corners of a square of side  ‘a’. Then potential at the center of the square is – 

A ] {V}_{0}=2(\frac {Q}{4\pi {\epsilon }_{{0}}\left({a∕\sqrt{{3}}}\right)})

B ] {V}_{0}=4(\frac {Q}{4\pi {\epsilon }_{{0}}\left({a∕\sqrt{{2}}}\right)})

C ] {V}_{0}=(\frac {Q}{4\pi {\epsilon }_{{0}}\left({a∕\sqrt{{3}}}\right)})

D ] {V}_{0}=3(\frac {Q}{4\pi {\epsilon }_{{0}}\left({a∕\sqrt{{2}}}\right)})

79 ] In the above case , the work done in removing a charge -Q from its center to infinity is

A ]  0
B ]  \frac {\sqrt{{2}}{Q}^{{2}}}{4\pi {\epsilon }_{{0}}a}
C ]  \frac {\sqrt{{2}}{Q}^{{2}}}{\pi {\epsilon }_{{0}}a}
D ] \frac {{Q}^{{2}}}{2\pi {\epsilon }_{{0}}a}

80 ] Two point charges 100 \mu{C} and 5\mu{C} are placed at points A and B respectively with AB=40 cm. The work done by external force in displacing the charge 5 \mu{C} from B to C, where BC= 30 cm , angle ABC =\frac {\pi }{2} and \frac {1}{4\pi {\epsilon }_{{0}}}={9}\times{10}^{9}N{m}^{2}/{C}^{2}

[ A ]  9J
[ B ]  \frac {81}{20}J
[ C ]  \frac {9}{25}J
[ D ]  -\frac {9}{4}J

81 ] The work done on rotating a point charge q around a charge Q in a circle of radius r is –  

[ A ]  {q}\times{2}\pi{r}
[ B ]  \frac {q\times 2\pi Q}{r}
[ C ]  zero
[ D ]  \frac {Q}{2{\epsilon }_{{0}}r}


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