Physics Engineering Entrance Questions

1. Three charges +4q, Q and q are placed in a straight line of length 1 at points distance 0, 1/2 and 1 respectively. What should beQ in order tc make the net force on q to be zero?
(a) —q (b) —2q (c) —q/2 (d) 4q
2. When a body is charged by induction, then the body:
(a) becomes neutral (b) does not lose any charge
(c) loses whole of the charge on it
(d) loses part of the charge on it
3. A given charge situated at a certain distance form an electric dipole in the end on position, experiences a force F. If the distance of charge is double, the force acting on the charge will be:
(a) 2F (b) F/2 (c) F/4 (d) F/8
4. An ebonite rod acquires a negative charge of 3.2 x 10-4° C. The number of excess electrons it has is:
(a) 2 x 109 (b) 2 x 1019 (c) 2 x 10-29 (d) 2 x 1029
5. Each of the two point charges are doubled and their distance is halved. Force of interaction becomes n times, where n is:
(a) 4 (b) 1 (c) 1/16 (d) 16
6. Two point charges of +21„tC and + 611 C repel each other with a force of 12 N. If each is given an additional charge of — 41,1C, then new force will be:
(a) — 4N (b) +4 N (c) 3 N (d) 48 N
7. Coulomb's law is given by F = kqlq,r n where n is:
(0 1/2 (b) —2 (c) 2 (d) —1/2
8. Two electrons are separated by a distance r metre and have coulomb force F. Two alpha particles separated by 2r metre will have a force equal to:
(a) 2F (b) 3F (c) F/2 (d) F
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9. The ratio of electric force between two electrons to two protons separated by the same distance in air is:
(a) 10° (b) 106 (c) 104 (d) none of the above
10. Two balls carrying charges +71..IC and —51i C attract each other with a force F. If a charge —21.1, C is added to both, the force between them will be:
(a) F (b) 512 (c) 2F (d) zero
11. The ratio of electric force between two protons to the gravitational force between them is of the order of
(a) 1042 (b) 1036 (c) 1029 (d) 1
12. If a charge is moving along the direction of Coulomb's force of an electric field:
(a) work is done by the electric field
(b) energy is used from some outside source
(c) strength of field decreases
(d) energy of the system is decreased
13. A positively charged ball hangs from a silk thread. We put a positive test charge go at a point and measure No, then it can be predicted that the electric field strength E will be:
, F, , F
va) (b) > c) < — (d) none of these
go qo go
14. The surface density of charge on the copper sphere is a. The electric field strength on the surface of the sphere is:
(a) 6 (b) 6/2 (c) 6/2 eo (d) olso
15. Two conducfing spheres of radii ri and r2 are charged to the same surface charge density. The ratio of electric fields near their surface is:
(a) ri2f/d
 (b) db.? (c) r /r, (d) 1:1
16. A hollow metallic sphere of radius 10 cm is given a charge of 3.2 x 10-9C. The electric intensity at a point 4 cm from the centre is: (a) 9 x 10-9 V (b) 288'V (c) 2.88 V (d) zero

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17. Two free protons are separated by a distance of 1A. If they are re-
0
leased, the kinetic energy of each proton when at infinite separation is:
(a) 11.5 x 10-19J (b) 23 x 10-19J
(c) 46 x 10-19J (d) 5.6 x 10-12'J
18. Two conducting spheres of radii r1 and r2are eqnally charged. The rati® of their potentials is
(a) ri /r2 (b) r2 /r1 (c) ri2/r2 2 (d) 1.2 22
19. Around a stationary charge of +211 C, another charge of —21,1, C is moved once round a circle of radius 5 cm, the amount of work done is
(a) zero (b) 1671/5J (c) 47E/5.1 (d) 811/5J
20. A uniform electric field having a magnitude E0 and direction along the positive x-axis exists. If the potential V, is zero at x = 0, then its value
x = +x will be
(a) V(x) = + xE® (b) V(x) = —xE0
(c) V(x) = —x2E02 (d) V(x) = +x2E02
21. An electron and a proton are situated in a uniform electric field. The ratio of their acceleration will be:
(a) zero (b) unity
(c) ratio of masses of proton and electron
(d) ratio of masses of electron and proton
22. A given charge is situated at a certain distance from an electric dipot, in the end-on-position, experiences a force F. If the distance of the charge is doubled, the force acting on the charge will be
(a) 2F (b) —2 (c) —5 (d) -F-8--
23. The SI unit of the line integral of electrical field is:
(a) NC-1 (b) Nm2C1 (c) JC-1 (d) Vm-1
24. A work of 100 joule is performed in carrying a charge of —5 coulomb from infinity to a particular point in an electrostatic field. Thep oten- tial of this point is: (a) 100 V (b) 5 V
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(b) 4nr2E (c) 2rtr2E (d) rcr2E
26. A sphere of radius lmencloses a charge of 5µC. Another charge of 51,1C is placed inside the sphere. The net electric flux would be :
(a) double (c) zero
2 Two thin infinite parallel sheets have uniform surface densities of
charge +a and —G. Electric field in the space between the two sheets
is
(a) 6/E0 (b) 6/2 eo (c) 20/60 (d) 46/c0
28. Twoplates are 1 cm apart and potential difference between them is 10 volt. The electric field between the plates is
(a) 10 N/C (I)) 500 N/C (c) 1000 N/C (d) 250 N/C
29. A 800F capacitor is charged at the steady rate of 501.1 Cisec. How long will it take to raise its potential to 10 volt?
(a) 160s (b) 50s (c) lOs (d) 500s
30. Two condensers of capacity 0.3 1.1,F and 0.60 respectively are connected in series The combination is connected across a poten tial of 6 volt. The ratio of energies stored by condensers will be
(a) 1/2 (b) 2 (c) 1/4 (d) 4
it.' Aparallel plate capacitor has a capacitance of
50 pF in air and 105 pF when immersed in oil. The dielectric con- stant of the oil is:
(a) 50/105 (b) I (c) 2.1 (d)
32. Taking earth to be a metallic sphere, its capacity will approxi mately be (Radius of earth = 6400 km)
(a) 6.4 x 106 F (b) 700 F (c) 7001AF (ti) 700 pF