**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 and 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 **

** (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 and 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 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 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, 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 atoms is transferred from one ball to the other, the coulomb force between them is (atomic weight of copper is 63.5)**

**A ] **

**B ] **

**C ] **

**D ] **

**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 ] **

**B ] **

**C ] **

**D ] **

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

**A ] 0**

**B ] **

**C ] **

**D ] **

**80 ] Two point charges 100 and 5 are placed at points A and B respectively with AB=40 cm. The work done by external force in displacing the charge 5 from B to C, where BC= 30 cm , angle and **

**[ A ] 9J**

**[ B ] **

**[ C ] **

**[ D ] **

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

**[ A ] **

**[ B ] **

**[ C ] zero**

**[ D ] **

** **