WAEC 2016 Physics · Question 1

Let x be the uncertainty in the measurements of position and p the uncertainty in measurement of momentum. The…

Question

Let Δ\Deltax be the uncertainty in the measurements of position and Δ\Deltap the uncertainty in measurement of momentum. The uncertainty principle relation is given as

  1. A.Δ\Deltax . Δ\Deltap = h
  2. B.Δ\Deltax . Δ\Deltap ≤\leq = h
  3. C.Δ\Deltax . Δ\Deltap ≥\geq = h
  4. D.Δ\Deltax . Δ\Deltap > h

Answer: C. Δ\Deltax . Δ\Deltap ≥\geq = h

Explanation written with AI and checked against the answer key

Analyze the question: The question asks for the correct mathematical statement of Heisenberg's Uncertainty Principle, relating the uncertainty in position (Δx) and the uncertainty in momentum (Δp).

Concept: Heisenberg's Uncertainty Principle says we cannot measure both the exact position and the exact momentum of a particle at the same time. The more precisely one is known, the less precisely the other can be known. The product of the two uncertainties therefore has a minimum value:

Δx · Δp ≥ ħ/2, where ħ = h/2π

In many WASSCE and school textbooks, this is written in the simpler order-of-magnitude form:

Δx · Δp ≥ h

Working through the options:

  • A (Δx·Δp = h): Wrong. The principle sets a lower limit, not an exact value.
  • B (Δx·Δp ≤ h): Wrong. This would put an upper limit on the product, and the principle says the opposite.
  • C (Δx·Δp ≥ h): Correct. The product can never be smaller than a minimum value of the order of h. This is the "greater than or equal to" form.
  • D (Δx·Δp > h): This is close, but it excludes the equality case. The principle allows the product to reach the minimum value, so "≥" is the better statement.

Answer: Option C.

Exam tip: Remember that the uncertainty principle sets a minimum on the product of uncertainties. Both quantities cannot be made arbitrarily small together, so the sign is always "≥" and never "≤".

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