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Question

If a scientist is comparing the energy output of two light bulbs and records their values in joules, which dimensional formula should be used to represent energy in the SI system?

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RRB NTPC 2025 Graduate CBT 2 Question Paper PDF (10-Jul-2026) (Shift 1)
The correct answer is

\([M L^2 T^{-2}]\)

Energy is defined as the capacity to do work, and work is force multiplied by displacement.

Force has the dimensional formula \([M L T^{-2}]\), so work (and hence energy) is \([M L T^{-2}] \times [L] = [M L^2 T^{-2}]\).

This matches the joule, the SI unit of energy, confirming the dimensional formula is unique among the given options.

Hence, the correct dimensional formula for energy is \([M L^2 T^{-2}]\).

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