Which one of the following is wrong?

1.	A comb run through one’s dry hair attracts small bits of paper.
2.	Ordinary rubber is an insulator. But special rubber tyres of aircraft are made slightly conducting.
3.	Vehicles carrying inflammable materials usually have metallic ropes touching the ground during motion.
4.	A bird perches on a bare high power line and gets a fatal shock. A man standing on the ground touches the same line and nothing happens to the man.

A slab of material of dielectric constant K has the same area as the plates of a parallel-plate capacitor of capacitance $C_0$ but has a thickness (3/4)d, where d is the separation of the plates. What is the capacitance of the capacitor when the slab is inserted between the plates?

$1. \left(\frac{4\mathrm{K}}{\mathrm{K}+3}\right){\mathrm{C}}_0$
$2. \left(\frac{2\mathrm{K}}{\mathrm{K}+2}\right){\mathrm{C}}_0$
$3. {\mathrm{C}}_0$
$4. \frac{3}{4}{\mathrm{C}}_0$

A network of four 10 µF capacitors is connected to a 500 V supply, as shown in the figure. The equivalent capacitance of the network is:

$1. \frac{10}{3}\mu F$
$2. \frac{20}{3}\mu F$
$3. \frac{40}{3}\mu F$
$4. \frac{16}{3}\mu F$

A network of four 10 µF capacitors is connected to a 500 V supply, as shown in the figure. The charge on the capacitor $\left(C_4\right)$ is: (Note, the charge on a capacitor is the charge on the plate with higher potential, equal and opposite to the charge on the plate with lower potential).

$1. 1.4\times {10}^{-3} C$
$2. 9\times {10}^{-4 }C$
$3. 1.7\times {10}^{-3} C$
$4. 5.0\times {10}^{-3} C$

A 900 pF capacitor is charged by a 100 V battery. The electrostatic energy is stored by the capacitor is U. If the capacitor is disconnected from the battery and connected to another 900 pF capacitor (as shown in the figure ) the electrostatic energy stored by the system is U'. The ratio of $\frac{U}{U\text{'}}$ is:

$1. \frac{2}{1}$
$2. \frac{1}{2}$
$3. 1$
$4. \frac{2}{3}$

Which of the following is NOT the property of equipotential surface?
1.  They do not cross each other.
2.  The rate of change of potential with distance on them is zero.
3.  For a uniform electric field they are concentric spheres.
4.  They can be imaginary spheres.

An electric dipole of moment p is placed parallel to the uniform electric field. The amount of work done in rotating the dipole by 90⁰ is-
1.  2pE
2.  pE
3.  pE/2
4.  Zero

Three capacitors 2µF, 3µF and 6µF are joined in series with each other. The equivalent capacitance is-
1.  1/2µF
2.  1µF
3.  2µF
4.  11µF

A capacitor plates are charged by a battery with ‘V’ volts. After charging battery is disconnected and a dielectric slab with dielectric constant ‘K’ is inserted between its plates, the potential across the plates of a capacitor will become
1.  Zero
2.  V/2
3.  V/K
4.  KV

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