RAS question
Heisenberg's Uncertainty Principle states that:
Correct answer: (B) Position and momentum of a particle cannot both be precisely known simultaneously.
Heisenberg's Uncertainty Principle states that a particle's position and momentum cannot both be known with arbitrary precision at the same time.
Explanation
Heisenberg's Uncertainty Principle is the quantum-mechanical limit expressed as Δx·Δp ≥ ℏ/2: the more precisely a particle's position is known, the less precisely its momentum can be known, and vice versa. The eGyanKosh unit states the same idea in plain terms: position and momentum cannot be simultaneously measured with arbitrarily high precision, and this is not merely a flaw in instruments or technique. It arises from the wave properties built into the quantum description of nature. That is why the principle is fundamental to quantum mechanics and why electrons are treated through probability clouds rather than fixed, precisely traceable paths.
Why the other options are wrong
- (A) Light travelling in straight lines is about rectilinear propagation of light, not the quantum limit on jointly knowing a particle's position and momentum.
- (C) Energy conservation is a separate physical principle; Heisenberg's statement here concerns the uncertainty relation between position and momentum.
- (D) Fixed electron orbits are the kind of precise path picture that the uncertainty principle undermines, since electron behaviour is described probabilistically rather than as exact orbits.
Concept
This tests the quantum mechanics part of General Science: uncertainty, wave-particle behaviour and the limits of classical descriptions. It recurs in RAS because exam questions often check whether candidates can distinguish modern physics principles from familiar school-level laws.