Suppose a speck of dust in an electrostatic precipitator has 1×1012 protons in it and has a net charge of −5.2 nC (a very large charge for a small speck). How many electrons does it have?

Explanation:

The given data is as follows.

          = -5.2 nC =  

          charge on an electron (e) =

Formula to calculate number of electrons is as follows.

               Q = ne

or,           n =

Putting the given values into the above formula as follows.

                n =

                   =

                   =

We know that when total charge is zero then number of protons is equal to the number of electrons.

That is,      

So, total number of electrons present are as follows.

                          =

Therefore, we can conclude that given speck of dust has electrons.

measuring things 1 litre of water