IB · D · multiple choice
Fields · Question 2
Fields · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 1
- Topics
- 1
- Answer
- Complete
Two identical conducting spheres carry charges of +6.0 nC and −2.0 nC. They are touched together and then separated to their original distance apart. How does the magnitude of the force between them change?
- A
It becomes zero.
- B
It is reduced to one third of its original value.
- C
It is reduced to one twelfth of its original value.
- D
It increases to twelve times its original value.
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Answer and reasoning
Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.
- 1
The correct choice is B: It is reduced to one third of its original value.
- 2
Touching shares the total charge of +4.0 nC equally, giving +2.0 nC on each, so the product of the charges falls from 12 nC² to 4 nC² and the force to one third. A is chosen by candidates who think the charges neutralise — they only partly do. The force also changes from attraction to repulsion, but the question asks about its magnitude.
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