Engineering Entrance Physics Questions

34. 64 identical drops of thercury are charged simultaneously to the same potential of 10 volts. Assuming the drops to be spherical, if all
the charged drops are made-to combine to form one large drop then its potential will be:
(a) 260 units (b) 320 units(c) 640 units (d) 160 units
35. A parallel plate capacitor having dielectric slab=of Er= 6 is connected across a battery and charged. This dielectric slab is then removed and new dielectric slab of Er= 10 is introduced. The ratio of energy stored in first case to that in second case is:
(a) 3 : 5 (b) 5 : 3 (c) 9 : 25(d) 25 : 9
36. The diameter of the plate of a parallel plate condenser is 6 cm. If its capacity is equal to that of a sphere of diameter 200 cm, the separa tion between the plates of the condenser is:
(a)45x10-4m 4.5x (b) 2.25 x 10-4m
(c) 6.75 x 10-4 m (d) 9 x 10-4m
37. There are 10 condensers each of capacity 5 1,,tE The ratio between max. and min. capacity obtained from these condensers will be (a) 25 : 5 (b) 40 : 1(c) 60 : 3 (d) 100 :
38. A hollow metal sphere of radius 30 cm is charged such that the
potential on its surface is 75 V. The potential at the centre of 'the sphere is:
(a) zero (b) 75 V (c) 225 V (d) 8V

40 A non-conducting solid sphere of radius R is uniformly charged. The magnitude of the electric field due to the sphere at a distance r from its centre:
(a) increases as r increases for r < R
(b) decreases as r increases for 0 < r <
(c) decreases as r increases for R < r
(d) is discontinuous at r = R
41. Number of electrons in one coulomb of charge will be: (a) 5.46 x 1029 (b) 6.25 x 1018 (c) 1.6.x 10+19 (d) 9 x 10"
42. A parallel, condenser with oil between the plates (dielectric constant of oil K = 2) has a capacitance C. If the oil is removed, then capacitance of the capacitor becomes:
C
(a) —
(b) (c) 2C (d) C
2
Two capacitors of 2µF and 41.,IF are connected in parallel. A third capacitor of 61,1F is connected in series. The combination is connected across a 12 V battery. The voltage across 2 idtF capacitor is: (a) 2 V (b) 8V (c) 6 V (d) 1 V
44. A technician has only two capacitors. By using these singly, in series or in parallel, he can obtain capacitances of 3 litF, 41,1F, 12 g and 161.iF. The capacitances of these capacitors are
(a) 6µF and 10 (b) 4µF and 12 i„IF
(c) 7µF and 9 (d) 4µF and 16 pf

46. An alpha particle is accelerated through a potential difference of 106 volt. Its kinetic energy will be:
(a) 1 MeV (b) 2 MeV (c) 4 MeV (d) 8 MeV
47. A hollow insulated conducting sphere is given a positive charge of
* lOktC. What will be the electric field at the centre of the sphere if its radius is 2 metres?
(a) zero (b) 51.tC m-2 (c) 8AC m'(d) 20ptC m-2
48. The number of lines of force coming out from a positive charge of one coulomb is: