# IIT JEE Advanced & Mains Physics 2018 : Electricity : Rankfile / expected questions

Primary Users : Students appearing for the Advanced and Mains Exam for Admission to the BTech Courses at the Indian Institutes of Technology , National Institutes of Technology , Indian Institute of Space science and Technology and other National Engineering Institutes, INDIA .

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P A G E  : 1

1.THE ATOMIC HOOK

Recently an Ice berg weighing around kgs broke off in the Weddell ice sea area in the Antarctic circle .Consider the following idea of an invention : A device consisting of two blocks – from one a proton can be extracted whose attractive force is directed towards an electron of the second block . Suppose the device is to be used as a hook  – that’s placing one block on the main ice and the second on the ice section which shows signs of breaking . What are your ideas regarding the following – [ neglect all other possible physical  forces / effects  ]

a } Would the device work as a hook preventing the breaking off of the above mentioned ice section ? If yes ,how many such devices would be needed  ?

b ]  What should be the effective weight of the blocks ?

c ] What is the effective distance needed between the blocks for such a device to work ?

d ] There is a very serious problem with the above idea .Can you point out what it is?

2.A negatively charged particle accelerates from East to West in a uniform electric field. What are the direction and the value of the electric field if the particle has charge q=6 μC, mass m=1 mg, and if the value of its acceleration is ? Select the closest answer: A) West, 0.001 N/C
B) East, 0.001 N/C
C) West, 3 N/C
D) East, 3 N/C
E) North, 300 N/C

3. A negatively charged particle with q= -3 μC is placed at the center of the uniformly charged cube with side a=1 mm and total charge Q=9 C spread out over all six faces of the cube. What is the total force acting on the particle in the center? Find the magnitude and the direction. (A) , left
(B) , right
(C) , top
(D) , bottom
(E) Zero

4 . A tiny particle with mass m=3 mg and positive charge Q=3 mC is placed just near the ground. Find the surface charge density on the ground for keeping the particle above it in a stationary position. Consider the ground to be a non-conductor.

(A) (B) (C) (D) (E)  5. Three charges , top of 6C and bottom two of charges of the same magnitude but of opposite sign are placed at the corners of an equilateral triangle with it’s side being d = 1 cm. . Find the value and the direction of the field exactly at the center of the triangle?

(A) , top
(B) , top
(C) , bottom
(D) , bottom
(E) None of the above

6. Some distance away from a positively charged plate with considerable surface charge density is placed an unit charge [ in mC ]  of mass  m=10 mg  on a wire  at an angle of 45 degrees.. Find the surface charge density .

(A) (B) (C) (D) (E) 7 . Charges are placed in a geometrical pattern corresponding to the  hour hands of a clock with their magnitudes being equivalent to that of the hours indicated .Calculate the resulting field ?

8. Consider a semicircle of radius r with it’s left quadrant being negatively charged and the rest being positive. .Find the field generated in this negative quadrant ?

9. A disc of radius r has an amount of charge q  uniformly spread on it’s surface  Find the potential at any point on it’s axis of symmetry.

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