A student wants to show that a field can affect objects in a region of space without direct contact. Which investigation would best provide this kind of evidence?
- Push a paper clip with a finger and observe it move across the table.
- Heat a metal rod and observe that it feels hot only when touched.
- Bring a charged rod near (but not touching) an electroscope and observe the leaves separate. (correct answer)
- Drop a rock and observe it fall straight down.
Explanation: This question tests understanding of how to collect qualitative evidence that electric or magnetic fields exist in the region around charges or magnets by observing how they affect objects placed in that region. Fields are invisible regions around sources (magnets, charged objects, masses) where forces exist and can affect objects—you cannot see fields directly, but you can detect them by placing test objects (compass, paper clips, electroscope, iron filings) at various positions and observing whether they respond: if compass needle deflects, magnetic field is present at that location; if electroscope leaves separate, electric field exists there; if paper clips are attracted, magnetic field extends to that position. Bringing a charged rod near (but not touching) an electroscope causes the metal leaves inside to separate—this demonstrates action at a distance through the electric field: the charged rod creates an electric field in surrounding space, the field extends across the gap to the electroscope, and the field exerts force on charges in the electroscope causing leaves to repel each other, all without any physical contact between rod and electroscope. This provides clear evidence that fields can affect objects in a region of space without direct contact. Choice C is correct because it accurately describes an investigation where a field (electric) affects an object (electroscope) across empty space without contact, directly demonstrating the key concept. Choice A involves direct contact (pushing with finger), not field effects at distance; Choice B requires touching to feel heat, not demonstrating action at distance; Choice D shows gravity but doesn't emphasize the field aspect or investigate it systematically. Field detection principles: fields mediate forces between objects without requiring contact—electric fields from charges affect other charges at distance, magnetic fields from magnets affect magnetic materials at distance, gravitational fields from masses affect other masses at distance. Real investigations demonstrating fields without contact: (1) charged rod near electroscope—leaves separate without touching, (2) magnet under paper with iron filings—filings align without touching magnet, (3) compass near magnet—needle deflects without contact, all showing that fields exist as regions of influence in space around sources, capable of exerting forces on appropriate objects placed within the field region.