Lines of force I. Begin and end on equal and opposite electric charges. II. are in state of tension which…

Analyze the question: This is about the properties of lines of force (field lines) in electric fields. We need to check each statement.

Concept: Properties of lines of force (Faraday's model)

1. They begin on positive charges and end on negative charges of equal magnitude (they never form closed loops in electrostatics).
2. They behave as if they are in tension along their length, like stretched elastic strings, so they tend to contract. This explains the attraction between unlike charges.
3. They repel one another sideways, so they never cross and they spread apart.

Check each statement:

• I. Begin and end on equal and opposite electric charges. This is correct. Lines start on a positive charge and end on an equal negative charge.
• II. Are in a state of tension which causes them to shorten. This is correct. Lines of force act like stretched rubber bands along their length and tend to shorten.
• III. Attract one another. This is false. Lines of force repel each other sideways, which is why they never intersect and why parallel lines spread out.

So statements I and II are correct, and III is incorrect.

Answer: D, I and II only.

Exam tip: Remember "tension along, pressure across." Lines of force pull lengthwise (contract) and push sideways (repel). If any statement says lines of force attract one another or cross, it is wrong.