Fundamental Concepts

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GRE Subject Test: Physics › Fundamental Concepts

Questions 1 - 2

What wavelength will result in the most accurate measurement of the momentum of an electron?

Radio

Red light

X-ray

Gamma-ray

Infrared

Explanation

The Heisenberg Uncertainty Principle states that:

$\Delta x \Delta p \ge \frac{\hbar}{2}.$ Since the uncertainty in the position is inversely proportional to the uncertainty in the momentum, we need to pick the longest wavelength. Of the options listed, radio has the longest wavelength.

Which of the following wavelengths could be used to measure the position of an electron with the greatest accuracy?

Gamma-rays

Infared

Radio

X-ray

Red light

Explanation

The Heisenberg Uncertainty principle states that

$\Delta x \Delta p \ge \frac{\hbar}{2}.$

Therefore, the smallest wavelength will have the lowest uncertainty in the position. Thus, we must pick the regime of options given which has the lowest wavelength. That is gamma-ray.

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