Which one of the following is not a property of the X-rays?
- (a)They are deflected by electric fields.
- (b)They are not deflected by magnetic fields.
- (c)They have high penetration length in matter.
- (d)Their wavelength is much smaller than that of visible light.
Correct — A, They are deflected by electric fields. X-rays are electromagnetic radiation, and electromagnetic radiation carries no electric charge. An electric field acts on charge, so it has nothing to grip; the same argument covers magnetic fields, which is why statement (b) is a true property and not the answer. This is the standard way of telling X-rays apart from beta rays and alpha rays, which are charged particles and do bend in both kinds of field. Statements (c) and (d) are also true — X-rays run from about 10 nanometres down to 10 picometres in wavelength, far shorter than visible light's 400 to 700 nanometres, and their penetrating power is what makes radiography possible.
- (b)They are not deflected by magnetic fields. — True, so it cannot be the answer to a not-a-property question. Being uncharged, X-rays ignore magnetic fields just as they ignore electric ones.
- (c)They have high penetration length in matter. — True. Hard X-rays traverse thick objects with little absorption, which is exactly why they are used to image the inside of bodies, welded joints and airport baggage.
- (d)Their wavelength is much smaller than that of visible light. — True. X-ray wavelengths are comparable to the spacing between atoms, which is why crystals diffract them and X-ray crystallography works.
X-rays sit between ultraviolet and gamma rays on the electromagnetic spectrum, roughly 10 nanometres to 10 picometres in wavelength and 100 eV to 100 keV in photon energy. Wilhelm Conrad Roentgen found them in 1895 and named them for their unknown nature. Because they are uncharged waves, no static electric or magnetic field bends their path; because their photons are energetic, they ionise matter, which is both their diagnostic value and their hazard.
The stem asks for the statement that is not a property, and three of the four are ordinary textbook facts, so the work is to spot the one inversion. Option (b) is written in the negative, and a candidate skimming for 'the odd one out' can be pulled towards it purely by its shape. The reliable test is the physics: an electric field and a magnetic field both act on moving charge, so any radiation that is uncharged is untouched by both. If you accept (b) as true, you must reject (a), because the two statements cannot both stand.
- X-rays were discovered by Wilhelm Conrad Roentgen in 1895.
- Their wavelength runs roughly from 10 nanometres down to 10 picometres — shorter than ultraviolet, longer than gamma rays.
- Being uncharged electromagnetic radiation, X-rays are deflected by neither electric nor magnetic fields.
- Photon energies of about 100 eV to 100 keV make X-rays ionising, which is why exposure is regulated.
- Hard X-rays have wavelengths near atomic spacings, which is the basis of X-ray crystallography.
- Being drawn to the negatively phrased option in a not-a-property item.
- Carrying over the behaviour of beta rays, which are electrons and do bend in a field, to X-rays.
- Confusing X-rays with gamma rays; they overlap in energy but differ in origin, X-rays from electron transitions and gamma rays from the nucleus.
As a which-statement-is-not-correct item on X-ray properties, or as a comparison of X-rays with visible light and ultraviolet by wavelength and energy.
Assertion (A): Radio waves bend in a magnetic field. Reason (R): Radio waves are electromagnetic in nature.
- (a) Both A and R are individually true and R is the correct explanation of A
- (b) Both A and R are individually true but R is not the correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true
Answer(d) A is false but R is true
The same physics set as an assertion-and-reason pair about radio waves. Being electromagnetic is true and being bent by a magnetic field is false, and the two do not connect — which is precisely why an X-ray, also electromagnetic, is not deflected either.
Consider the following statements about visible light, UV light and X-rays : 1. The wavelength of visible light is more than that of X-rays. 2. The energy of X-ray photons is higher than that of UV light photons. 3. The energy of UV light photons is less than that of visible light photons. Which of the statements given above is/are correct?
- (a) 1, 2 and 3
- (b) 1 and 2 only
- (c) 2 and 3 only
- (d) 1 only
Answer(b) 1 and 2 only
Tests the wavelength and energy half of this item. Ranking visible light, ultraviolet and X-rays by wavelength and by photon energy is the same knowledge that makes statement (d) here a true property.
- practice — not a real PYQ
A beam of X-rays is passed through a strong magnetic field. The beam will
- (a)bend towards the north pole
- (b)bend towards the south pole
- (c)travel undeviated
- (d)split into two beams
Answer(c) travel undeviated — X-rays carry no charge, so a magnetic field exerts no force on them.
- practice — not a real PYQ
Which one of the following properties of X-rays makes them suitable for studying the structure of crystals?
- (a)They travel in straight lines
- (b)Their wavelength is comparable to the spacing between atoms
- (c)They are invisible to the eye
- (d)They can be produced in a vacuum tube
Answer(b) Their wavelength is comparable to the spacing between atoms — that is the condition for a crystal lattice to diffract them.