1. which combination of four identical capacitors (of all possible combinations) has maximum capa

citance? if these combinations are connected to a constant P.d., which combination store minimum energy?

2. can negative ions be accelerated using Van de Graaff generator? why?

3. On which principle ink jet printing and xerox copying machine works?

 Hi,       

Capacitances connected in parallel will have the maximum capacitance.

Equivalent capacitance (c) is given as:

c = C + C+C+C where C is the value of each identical capacitance.

= 4C which can be the maximum possible value.

The minimum value of capacitance :

1/C = 1/C +1/C +1/C +1/C

c = C/4

now energy Q is given as:

Q = ½ cV²

Hence minimum energy at constant potential difference V will be when value of capacitance is minimum. Ie;

Q = ½ (C/4)V²

Hence series connection will have minimum potential energy.

2^nd case

Van de graaff generator can be used to accelerate negative charges also. In the generator , in general at first positive potential V is supplied which is given as

V = Q/C where Q is the charge and C is the capacitance of the sphere. Hence as Q is increased, V will go on increasing.

If we have to accelerate a negative charge, then negative potential must be supplied. This will in turn induce a negative charge. Hence the only difference is that negative potential –V is supplied in this case.

3^rd case

Inkjet (or ink jet) printers operate by propelling tiny droplets of liquid ink onto paper to form characters. There are three types of ink jets:

Thermal

Piezoelectric

Continuous

Here we will discuss briefly the thermal ink jet printer

There is a print catridge with a series of thermal heat chambers which are inturn produced by photolithography ie taking an image of the paper to be printed. Now to produce an image of the material to be printed, the printer runs an electric pulse through the heat chambers.  A steam "explosion" in the chamber forms a bubble, which propels a droplet of ink onto the paper. The ink's surface tension pulls another charge of ink into the chamber through a narrow channel attached to an ink reservoir.  In this manner the whole material gets printed.

Working of Xerox machine:

Photoconductivity is the principle on which a Xerox machine works. A photo conductor is a semiconductor which conducts electricity when exposed to light. A photoconductive drum is used in such a machine.

Now when a document is to be photocopied, a bright beam of light falls on the document which reflects the white part of the document to the photoconductive drum . the areas of the drum get conductive and charged. All the charge produced is discharged to ground and the written part ie the black part  gets negatively charged hence an image is produced on the photoconductive drum.