I'll work through this step-by-step to solve the electrostatics problem.
Understanding the Setup:
- Initial metal sphere is neutral with 8 protons (and therefore 8 electrons)
- Aluminum rod rubbed with carbon will become charged
- We need to determine what type of charging occurs and track charges through all stages
Step 1: Determine what happens when aluminum is rubbed with carbon
When materials are rubbed together, one becomes positively charged and the other negatively charged based on the triboelectric series. Carbon tends to gain electrons more easily than aluminum, so:
- Carbon gains electrons → becomes negative
- Aluminum loses electrons → becomes positive
So the aluminum rod becomes
positively charged.
Step 2: Identify the charging method
Looking at the process:
- Stage I: Neutral sphere
- Stage II: Charged rod brought close (but not touching)
- Stage III: Rod touches the sphere
- Stage IV: Rod removed
Since the rod actually
touches the sphere in Stage III, this is
charging by conduction (also called contact).
Step 3: Track charges through each stage
Stage I - Initial Metal Sphere:
- Neutral
- 8 protons (+) and 8 electrons (-)
- Net charge = 0
Stage II - Rod brought close:
- The positive aluminum rod attracts electrons in the metal sphere
- Electrons move toward the side closest to the rod
- Protons stay fixed (they can't move in solids)
- This creates charge separation but the sphere is still neutral overall
- Near side: excess electrons (negative)
- Far side: deficit of electrons (positive)
Stage III - Rod touches sphere:
- When they touch, electrons flow from the sphere to the positive rod
- The positive rod wants electrons, so it pulls them from the sphere
- Some electrons leave the sphere and go onto the rod
- Now the sphere has fewer electrons than protons
Stage IV - Rod removed:
- The rod takes its borrowed electrons with it
- The sphere now has a permanent positive charge
- If electrons left the sphere, it has more protons than electrons
Determining the final charge:
In charging by conduction with a positive object:
- Electrons transfer FROM the neutral object TO the positive object
- The neutral object loses electrons
- Losing negative charges makes it positive
Since the aluminum rod is positive and touched the sphere, electrons moved from the sphere to the rod. The sphere lost some electrons.
If we assume some electrons transferred (let's say 2-4 electrons typically transfer in such demonstrations), the sphere would have:
- Still 8 protons
- Fewer than 8 electrons (maybe 6 or so)
- Net positive charge
The final charge on the metal sphere is
positive (or
+).
More specifically, if we need to indicate the actual charge value and assuming typical electron transfer, it would be approximately
+2e to +4e (where e is the elementary charge), but since the problem doesn't specify exact numbers of transferred electrons, we indicate it as
positive.
Let me reconsider - the problem asks for "ALL pertinent charges" which means showing the distribution. Let me think about what should be drawn:
For the diagrams:
- Stage I: 8+ and 8- distributed evenly (neutral)
- Stage II: 8+ fixed, 8- shifted toward rod side (polarized but neutral)
- Stage III: During contact, some electrons flow to rod
- Stage IV: Sphere has 8+ and fewer than 8- (net positive)
Final Answer:
Process A – Charging by:
conduction (or
contact)
Final Charge on the Metal Sphere is:
positive (or
+)
Parent Tip: Review the logic above to help your child master the concept of electrostatics worksheet.
