Electric Charges and Fields

A point particle of charge Q is located at P along the axis of an electric dipole 1 at a distance r as shown in the figure. The point P is also on the equatorial plane of a second electric dipole 2 at a distance r. The dipoles are made of opposite charge q separated by a distance 2a. For the charge particle at P not to experience any net force, which of the following correctly describes the situation? [figure]

1. ar 0.5
2. ar 3
3. ar 10
4. ar 20

A positive ion A and a negative ion B has charges 6.67 10-19 C and 9.6 10-10 C, and masses 19.2 10-27 kg and 9 10-27 kg respectively. At an instant, the ions are separated by a certain distance r. At that instant the ratio of the magnitudes of electrostatic force to gravitational force is P 10-13, where the value of P is . (Take 14 0=9 109 Nm2C-2 and universal gravitational constant as 6.67 10-11 Nm2 kg-2 )

A line charge of length a2 is kept at the center of an edge BC of a cube ABCDEFGH having edge length ' a ' as shown in the figure. If the density of line charge is C per unit length, then the total electric flux through all the faces of the cube will be . (Take, 0 as the free space permittivity) [figure]

1. a2 0
2. a8 0
3. a4 0
4. a16 0

An electron is made to enter symmetrically between two parallel and equally but oppositely charged metal plates, each of 10 cm length. The electron emerges out of the electric field region with a horizontal component of velocity 106 m/s. If the magnitude of the electric field between the plates is 9.1 V/cm, then the vertical component of velocity of electron is (mass of electron =9.1 10-31 kg and charge of electron =1.6 10-19 C )

1. 1 106 m/s
2. 16 106 m/s
3. 16 104 m/s
4. 0