If the value of a physical quantity in the new system of units is related to its value in the old system by X_new = k X_old, then k would be 1/2. The unit itself becomes 2 times larger. Let's make sure the question and option are perfectly aligned. Let's rephrase the question to avoid ambiguity. Question 45 (Revised): If the unit of length is doubled and the unit of mass is halved, while the unit of time remains the same, how does the *magnitude* of power (numerical value) for a given physical quantity change?

4 views 1 helpful Updated Jul 27, 2026
Appears in NEET UG
Solution ✔ Verified
  • ABecomes 1/4th
  • BBecomes 1/2
  • CBecomes 2 times
  • DBecomes 4 times
Explanation

The dimensional formula for Power is [M L² T^-3]. Let the old unit of power be P_old = M L² T^-3. The new unit of mass is M' = M/2, and the new unit of length is L' = 2L. The new unit of power P_new = M' (L')² T^-3 = (M/2) * (2L)² * T^-3 = (1/2) * 4 * (M L² T^-3) = 2 * P_old. This means the new unit of power is twice as large as the old unit. If the unit becomes 2 times larger, the numerical value of a given physical quantity will become 1/2 times its original value (e.g., if 10 J/s = 5 P_new, then P_new is twice P_old). Thus, the magnitude of power becomes 1/2 times.

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