Electric Charges and Fields · Question 10

Two short dipoles (A, B), A having charges 2 and length 1 cm and B having charges 4 and length 1 cm are placed with their centres 80 cm apart as shown in the figure. The electric field at a point P, equi-distant from the centres of both dipoles is N/C. [figure]

1. 916 2 105
2. 916 2 104
3. 9 2 104
4. 4.5 2 104

A simple pendulum has a bob with mass m and charge q. The pendulum string has negligible mass. When a uniform and horizontal electric field E is applied, the tension in the string changes. The final tension in the string, when pendulum attains an equilibrium position is .

1. mg - qE
2. m2g2 + q2E2
3. mg + qE
4. m2g2 - q2E2

Six point charges are kept 60 apart from each other on the circumference of a circle of radius R as shown in figure. The net electric field at the center of the circle is . ( 0 is permittivity of free space) [figure]

1. - ( 5Q8 0 R2 )( i - 3 j)
2. Q4 0 R2( 3 i - j)
3. - Q4 0 R2( 3 i - j)
4. - 5Q8 0 R2( i + 3 j)

An infinitely long wire has uniform linear charge density = 2 nC/m. The net flux through a Gaussian cube of side length 3 cm, if the wire passes through any two corners of the cube, that are maximally displaced from each other, would be x N m2 C-1, where x is: [Neglect any edge effects and use 14 0 = 9 109 SI units]

1. 6.48
2. 0.72
3. 1.44
4. 2.16

A dipole with two electric charges of 2 magnitude each, with separation distance 0.5 , is placed between the plates of a capacitor such that its axis is parallel to an electric field established between the plates when a potential difference of 5 V is applied. Separation between the plates is 0.5 mm. If the dipole is rotated by 30 from the axis, it tends to realign in the direction due to a torque. The value of torque is:

1. 2.5 10-9 Nm
2. 2.5 10-12 Nm
3. 5 10-3 Nm
4. 5 10-9 Nm

The electric field in a region is given by E = (2 i + 4 j + 6 k) 103 N/C. The flux of the field through a rectangular surface parallel to x–z plane is 6.0 Nm2C-1. The area of the surface is cm2.

Two infinite identical charged sheets and a charged spherical body of charge density ' ' are arranged as shown in figure. Then the correct relation between the electrical fields at A, B, C and D points is: [figure]

1. | EA | = | EB |; EC > ED
2. EA = EB; EC = ED
3. EC ED; EA > EB
4. EA > EB; EC = ED

Two small spherical balls of mass 10 g each with charges -2 and 2 , are attached to two ends of very light rigid rod of length 20 cm. The arrangement is now placed near an infinite non-conducting charge sheet with uniform charge density of 100 /m2 such that length of rod makes an angle of 30 with electric field generated by charge sheet. Net torque acting on the rod is: (Take 0 = 8.85 10-12 C2/Nm2)

1. 1.12 Nm
2. 2.24 Nm
3. 11.2 Nm
4. 112 Nm

A metallic ring is uniformly charged as shown in figure. AC and BD are two mutually perpendicular diameters. Electric field due to arc AB at 'O' is 'E' in magnitude. What would be the magnitude of electric field at 'O' due to arc ABC ? [figure]

1. 2E
2. Zero
3. E/2
4. 2E

Consider two infinitely large plane parallel conducting plates as shown below. The plates are uniformly charged with a surface charge density + and -2 . The force experienced by a point charge +q placed at the mid point between two plates will be: [figure]

1. 3 q4 0
2. 3 q2 0
3. q4 0
4. q2 0