The electroscope detects

Question

BlackTom AI · Accepted Answer

An electroscope detects the presence and quantity of electric charge — i.e., static electricity.

1) Relevant concepts: An electroscope is a device (metal knob, conducting rod, and two thin leaves) that responds to excess electric charge on a conductor. Like charges repel; when charge is present on the electroscope, the two leaves acquire the same sign and repel, causing leaf divergence. The device therefore senses static (stationary) charge accumulation, not a continuous flow of charge.

2) Step‑by‑step reasoning:
- If a charged object is brought near or touches the knob, charge is transferred or redistributed on the electroscope.
- The leaves acquire charge of the same sign and repel each other, producing a visible separation. The degree of divergence indicates the amount of charge.
- This behavior relies on electrostatic forces between charges at rest (Coulomb repulsion), so the electroscope is responding to static electric charge.

3) Calculations: No numerical calculations are required; the observable effect (leaf divergence) is the measurement.

4) Why the correct answer is correct: Option (a) “static electricity” correctly names what the electroscope detects — accumulated electric charge at rest. The device gives a visual indication of the presence and relative magnitude of static charge on the conductor.

5) Why the other options are incorrect:
- (b) “positive charges only” is incorrect because an electroscope responds to both positive and negative charges. With a known charged object or by using induction, one can determine sign, but the device itself is not limited to detecting only positive charge.
- (c) “electric current” is incorrect because current is moving charge (flow per unit time); an electroscope measures stationary charge accumulation, not a continuous current.
- (d) “negative charges only” is incorrect for the same reason as (b): it detects either sign of static charge, not just negative.

Conclusion: The electroscope detects static electricity, so the correct answer is (a) static electricity, matching the provided answer.

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