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Q30 (CDS-I/2017) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Waves and acoustics Answer Verified

A photon of X-ray has energy of 1 keV. A photon of visible radiation has energy of 3 eV. In this context, which one of the following statements is not correct?

Result
Your answer: —  ·  Correct: C
Explanation

The energy of a photon is directly proportional to its frequency (E = hν) and inversely proportional to its wavelength (E = hc/λ) [3]. An X-ray photon with 1 keV (1000 eV) has significantly higher energy than a visible radiation photon with 3 eV. Consequently, the X-ray photon has a higher frequency and a shorter (lesser) wavelength compared to the visible photon. Statements 1, 2, and 4 are therefore scientifically correct. However, statement 3 is incorrect because all electromagnetic radiations, including X-rays and visible light, travel at the same constant speed in a vacuum, which is approximately 3 × 10⁸ m/s (denoted as 'c') [3]. The speed of a photon in a vacuum is independent of its energy, frequency, or wavelength.

Sources

  1. [3] https://www.sciencedirect.com/topics/engineering/photon-energy
  2. [2] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > What you have learnt > p. 159
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