64. Three charges each of +2 C -are placed at the three corners of an equilateral triangle. It the force between any two charges is F, then net force on any charge is

A.2Qq

B. 3Qq

C. 4Qq

D. 5Qq

65. Three small sized insulated spheres each carrying a charge +q are placed at three points on the circumference of a circle so as to form an equilateral triangle. If R is the radius of the circle, what will be the force on charge +Q placed at the centre of the circle?

A. zero

B.4neOR2

C. 4rce0R2

D. 4ne0R2

66. An electron is accelerated through a potential difference of 12000 V. Its initial velocity is le ms-1. The final velocity of the electron will be

A. 4.2 x 105 ms-1

B. 3-2 ms-I

C. 0.465 x 108 ms-1

D. 0.215 ms-1

67. An electron is accelerated through 1 V. The velocity of electron is about

A. 3 x 108 ms -I

B. 6 x 104 ms-I

C. 2.8 x 106 ms-1

D. 6 x 105 ms-I

68. A particle carrying a charge of 10 C begins to move in a uniform electric field of strength 50 Vm-1. After travelling a distance of 1 m, the kinetic energy of the particle will be

A. 5 x 10-4 J

B. 2.5 x 103 J

C. 50 eV

D. 3.4 x 10-2 J

69. A unit charge moves on an equipotential surface from point A to point B. Then

A. VA - VB = 0

B. VA - VB = +ve

C. VA - VB = -ve

D. none of above

70. The dissipation factor of a good dielectric is of the order of

A. zero

B. perpendicular to side AB

C. along the diagonal AC

D. along the diagonal BD

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