Exam-style question
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In a twin paradox scenario, which time interval corresponds to proper time?.
- A.time measured by the traveling twin
- B.time measured by the stationary twin
- C.time measured by an observer in a different inertial frame
- D.time measured by a photon
Model answer
What a good answer should say
- time measured by the stationary twin
Explanation
Why this works
Formula/rule: Δτ = Δt / γ. Substitution: For the stationary twin, v = 0 so γ = 1.
Working: Δτ = Δt / 1 = Δt. Answer: the stationary twin’s clock records the proper time of the events.
Units/conclusion: proper time is measured in seconds and equals the coordinate time for the stationary observer.
Common mistake
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