16.4 CHAPTER 16. ELECTROSTATICS
Step 3:Apply the principles: redistributing charge
As the spheres are identical in material, size and shape the charge
will redistribute across the two spheres so that it is shared evenly. Each
sphere will have half of the total charge:Q=Q^1 + 2 Q^2=−^9.^6 ×^10− (^18) +(− 4 , 8 × 10 − 18 )
2
= 7, 2 × 10 −^18 C
So each sphere now has:
7 , 2 × 10 −^18 C
of charge.
We know that charge is quantised and that electrons carry the base unit
of charge which is− 1 , 6 × 10 −^19 C.
Step 4:Apply the principles: charge quantisation
As each electron carries the same charge the total charge must be made
up of a certain number of electrons. To determine how many electrons
we divide the total charge by the charge on a single electron:
N=−^7 ,^2 ×^10
− 18
− 1 , 6 × 10 −^19
= 45electrons
Investigation: The electroscope
The electroscope is a very sensitive instrument which can be used
to detect electric charge. A diagram of a gold leaf electroscope is shown
the figure below. The electroscope consists of a glass container with a
metal rod inside which has 2 thin pieces of gold foil attached. The other
end of the metal rod has a metal plate attached to it outside the glass
container.
272 Physics: Electricity and Magnetism