Electric Charges and Fields

Two charges q and 3q are separated by a distance 'r' in air. At a distance x from charge q, the resultant electric field is zero. The value of x is :

1. r3(1+ 3)
2. (1+ 3)r
3. r(1+ 3)
4. r(1+ 3)

Force between two point charges q1 and q2 placed in vacuum at 'r' cm apart is F. Force between them when placed in a medium having dielectric constant K=5 at 'r/5' cm apart will be:

1. 5F
2. 25F
3. F/5
4. F/25

A particle of charge '-q' and mass 'm' moves in a circle of radius 'r' around an infinitely long line charge of linear charge density '+ '. Then time period will be given as : (Consider k as Coulomb's constant)

1. T2= 4 2m2k qr3
2. T= 12 r m2k q
3. T= 12 2k qm
4. T=2 r m2k q

Two identical charged spheres are suspended by strings of equal lengths. The strings make an angle of 37 with each other. When suspended in a liquid of density 0.7 g/cm3, the angle remains same. If density of material of the sphere is 1.4 g/cm3, the dielectric constant of the liquid is ( 37 = 34 )

Two charges of 5Q and -2Q are situated at the points (3a,0) and (-5a,0) respectively. The electric flux through a sphere of radius '4a' having center at origin is :

1. 2Q 0
2. 7Q 0
3. 3Q 0
4. 5Q 0

An electron is moving under the influence of the electric field of a uniformly charged infinite plane sheet S having surface charge density + . The electron at t=0 is at a distance of 1 m from S and has a speed of 1 m/s. The maximum value of if the electron strikes S at t=1 s is [ m 0e ] Cm2, the value of is .

An electric field is given by (6 i+5 j+3 k) N/C. The electric flux through a surface area 30 i m2 lying in YZ-plane (in SI unit) is :

1. 60
2. 90
3. 180
4. 150

A thin metallic wire having cross sectional area of 10-4 m2 is used to make a ring of radius 30 cm. A positive charge of 2 C is uniformly distributed over the ring, while another positive charge of 30 pC is kept at the centre of the ring. The tension in the ring is N; provided that the ring does not get deformed (neglect the influence of gravity). (given, 14 0 = 9 109 SI units)

Two charges of -4 and +4 are placed at the points A(1, 0, 4) m and B(2, -1, 5) m located in an electric field E=0.20 i V/cm. The magnitude of the torque acting on the dipole is 8 10-5 Nm, where = .