One of the properties associated with X-rays is that they can be deflected by

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Correct — D, None of the above. X-rays are electromagnetic radiation — the same kind of thing as light, radio waves and gamma rays, differing only in wavelength, which for X-rays runs from about 0.01 to 10 nanometres. Electromagnetic radiation is carried by photons, and a photon has no electric charge and no magnetic moment. The force that bends a beam in a field is the Lorentz force, F = q(E + v × B), and every term in it is multiplied by the charge q. Put q = 0 and the force vanishes identically: an X-ray beam passes through an electric field and through a magnetic field without the slightest deviation. So all three of the field options fail, and the escape option is the correct one. This is not a technicality — non-deflection is precisely how X-rays were identified. Wilhelm Conrad Röntgen discovered them in November 1895 and called them X-rays because he did not know what they were; the decisive experiment that separated them from cathode rays was that cathode rays bend sharply in a magnetic field while the new rays did not bend at all. The same test sorts radioactivity into its three classes: alpha particles, carrying charge +2e, curve one way; beta particles, carrying −e, curve the other way and much more sharply because they are far lighter; gamma rays, being photons, go straight through undeviated. X-rays behave exactly like gamma rays in this respect. Note carefully what the answer does NOT claim. X-rays interact with matter in several strong ways — they are absorbed heavily by high atomic-number elements such as calcium and barium, which is what makes a radiograph; they are diffracted by the regular planes of a crystal, which is the basis of X-ray crystallography; and they scatter off electrons with a change of wavelength in the Compton effect. None of that is deflection by an electric or magnetic field, which is what the stem asks about.

Why the other options are wrong — (a) Describes a beam of charged particles, not X-rays. Cathode rays — streams of electrons — are deflected by a magnetic field, and J. J. Thomson used exactly that deflection, balanced against an electric field, to measure the electron's charge-to-mass ratio in 1897. An X-ray beam put through the same apparatus does not move at all.  (b) The most confident-sounding wrong answer, and it is the correct description of a charged particle beam, which responds to both fields. Since an X-ray photon carries no charge, doubling the number of fields does not help: zero force from the electric field plus zero force from the magnetic field is still zero.  (c) Fails for the same reason. An electric field exerts a force qE on a particle, and q is zero for a photon. Canal rays, or anode rays, which are positive ions, are the beam that this option would correctly describe — and their deflection in electric and magnetic fields is how isotopes were first separated in a mass spectrograph.

Concept: The electromagnetic spectrum is a single family of waves ordered by wavelength: radio, microwave, infrared, visible light, ultraviolet, X-rays, gamma rays. Every member travels at the speed of light in vacuum, every member is uncharged, and therefore no member of the family is deflected by an electric or magnetic field. What distinguishes X-rays within that family is photon energy. Their wavelengths are comparable to the spacing between atoms in a solid, which has two consequences that define their uses. First, they are energetic enough to pass through soft tissue while being strongly absorbed by heavier elements, so bone and metal cast shadows — the basis of radiography and of computed tomography. Second, because their wavelength matches the crystal lattice spacing, crystals diffract them according to Bragg's law, nλ = 2d sin θ, which is how the atomic structure of salts, metals, proteins and famously DNA was determined.

State PCS 2025 Q15 — Science & Technology PYQ with Answer

State PCS 2025 Q15 — Science & Technology PYQ with Answer