Everything Science Grade 10

16.4 CHAPTER 16. ELECTROSTATICS

move freely. When they touch nothing will happen.

Example 6: Identical spheres sharing charge II

QUESTION

Two identical, metal spheres on insulating stands have different charges. Sphere 1

has a charge of− 9 , 6 × 10 −^18 C. Sphere 2 has 60 excess protons. If the two spheres

are brought into contact and then separated, what charge will each have? How

many electrons or protons does this correspond to?

SOLUTION

Step 1:Analyse the question

We need to determine what will happen to the charge when the spheres

touch. They are metal spheres so we know they will be conductors.

This means that the charge is able to move so when they touch it is

possible for the charge on each sphere to change. We know that charge

will redistribute evenly across the two spheres because of the forces

between the charges. We need to know the charge on each sphere, we

have been given one.

Step 2:Identify the principles involved

This problem is similar to the earlier worked example. This time we

have to determine the total charge given a certain number of protons.

We know that charge is quantised and that protons carry the base unit

of charge and are positive so it is+1, 6 × 10 −^19 C.

Step 3:Apply the principles

The total charge will therefore be:

Q 2 = 60× 1 , 6 × 10 −^19 C

= 9, 6 × 10 −^18 C

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

270 Physics: Electricity and Magnetism