Electrostatic Potential and Capacitance · Question 20

The distance between the two plates of a parallel plate capacitor is doubled and the area of each plate is halved. If C is its initial capacitance, its final capacitance is equal to

1. C4
2. 2C
3. C2
4. 4C

The effective capacitances of two capacitors are 3 and 16 , when they are connected in series and parallel respectively. The capacitance of two capacitors are :

1. 1.2 , 1.8
2. 10 , 6
3. 8 , 8
4. 12 , 4

Six charges +q, -q, +q, -q, +q, and -q are fixed at the corners of a hexagon of side d as shown in the figure. The work done in bringing a charge q0 to the centre of the hexagon from infinity is ( 0 - permittivity of free space) [figure]

1. -q24 0 d (6 - 1 2 )
2. Zero
3. -q24 0 d
4. -q24 0 d (3 - 1 2 )

A parallel plate capacitor has a uniform electric field E in the space between the plates. If the distance between the plates is 'd' and the area of each plate is 'A', the energy stored in the capacitor is : ( 0 = permittivity of free space)

1. E2Ad 0
2. 12 0E2
3. 0EAd
4. 12 0E2Ad

Polar molecules are the molecules :

1. having a permanent electric dipole moment
2. having zero dipole moment
3. acquire a dipole moment only in the presence of electric field due to displacement of charges
4. acquire a dipole moment only when magnetic field is absent

Two charged spherical conductors of radius R1 and R2 are connected by a wire. Then the ratio of surface charge densities of the spheres ( 1 / 2) is :

1. R12R22
2. R1R2
3. R2R1
4. ( R1R2 )

The equivalent capacitance of the combination shown in the figure is : [figure]

1. 3C/2
2. 3C
3. 2C
4. C/2

Twenty seven drops of same size are charged at 220 V each. They combine to form a bigger drop. Calculate the potential of the bigger drop.

1. 1980 V
2. 660 V
3. 1320 V
4. 1520 V

A short electric dipole has a dipole moment of 16 10-9 C m. The electric potential due to the dipole at a point at a distance of 0.6 m from the centre of the dipole, situated on a line making an angle of 60 with the dipole axis is : ( 14 0 = 9 109 N m2/C2 )

1. 200 V
2. 400 V
3. zero
4. 50 V

The capacitance of a parallel plate capacitor with air as medium is 6 . With the introduction of a dielectric medium, the capacitance becomes 30 . The permittivity of the medium is : ( 0 = 8.85 10-12 C2 N-1 m-2)

1. 1.77 10-12 C2 N-1 m-2
2. 0.44 10-10 C2 N-1 m-2
3. 5.00 C2 N-1 m-2
4. 0.44 10-13 C2 N-1 m-2