Physics · Electromagnetic Waves · NEET
You take high-energy (fast) electrons and make them hit a metal target. When these electrons hit the metal and stop very suddenly, they lose their kinetic energy. This lost energy comes out as X-ray photons. In NCERT words: 'bombard a metal target by high energy electrons.' So the source is decelerating (rapidly stopping) electrons, not the nucleus.
NCERT gives the X-ray region as about 10^-8 m (10 nm) down to 10^-13 m. In NEET spectrum-matching questions X-rays are usually taken as ~10^-10 m. They sit just beyond ultraviolet on the short-wavelength (high-frequency, high-energy) side of the spectrum.
When an electron is accelerated through a potential difference V, it gains kinetic energy eV. In the most extreme case, all of this energy goes into one single X-ray photon of energy hc/λ. Setting eV = hc/λ_min gives λ_min = hc/(eV). So λ_min is inversely proportional to V: a higher tube voltage gives shorter (harder) X-rays.
Both are EM waves, but they differ by source. X-rays come from heavy atoms / fast electrons hitting a target. Gamma rays come from the atomic nucleus (radioactive decay). Gamma rays also have shorter wavelength (higher energy) than X-rays. For NEET, remember: X-rays = electron/atom origin; gamma = nuclear origin.
X-rays carry high energy per photon, so they can damage or destroy living tissue and cells. That is exactly why they can treat cancer (kill malignant cells), but it is also why overexposure is dangerous. NCERT warns: 'care must be taken to avoid unnecessary or over exposure.'
Match List I (Electromagnetic waves) with List II (Wavelength): (a) AM radio waves (b) Microwaves (c) Infrared waves (d) X-rays; (i) 10^-10 m (ii) 10^2 m (iii) 10^-2 m (iv) 10^-4 m.
The minimum wavelength of X-rays produced by an electron accelerated through a potential difference of V volts is proportional to:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Between ultraviolet rays and gamma rays. In order of increasing wavelength: gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, radio waves. X-rays have very short wavelength (~10^-8 to 10^-13 m) and high frequency.
Medical diagnosis (imaging bones and internal organs) and treatment of certain cancers. They are also used in security scanning and studying crystal structures, but for NEET focus on the NCERT points: diagnostic tool and cancer treatment.
No. Like all electromagnetic waves, X-rays travel through vacuum at the speed of light c = 3 × 10^8 m/s. They do not need any material medium.
Their short wavelength and high energy let them pass through soft tissue, but denser material like bone absorbs more of them. This difference in absorption creates the shadow image on the film, which is how an X-ray photograph is formed.
Yes. λ_min is the sharp short-wavelength cutoff of the continuous X-ray spectrum. No X-ray shorter than this can appear because a single photon cannot carry more energy than the whole electron energy eV.
