Question 71 markMCQSection A

Electromagnetic waves used in a diagnostic tool in medicine have a wavelength range

Electromagnetic Waves
Electromagnetic Spectrum — X-rays

Options

(A)1 nm to 10−310^{-3} nm
(B)400 nm to 1 nm
(C)1 mm to 700 nm
(D)0.1 m to 1 mm

Official answer

Correct option: (A) 1 nm to 10−310^{-3} nm


The diagnostic tool referred to is the X-ray, used in medicine for radiography (bone imaging, CT scans).


  • X-rays occupy the wavelength band roughly 1 nm down to 10−310^{-3} nm (10−910^{-9} m to 10−1210^{-12} m), lying between ultraviolet and gamma rays.
  • Their short wavelength gives high penetrating power, letting them pass through soft tissue but be absorbed by dense bone.
Answer keywords:X-raysdiagnostic toolwavelength range1 nm to 10^-3 nmelectromagnetic spectrumradiographypenetrating powermedicine

Marking scheme

  1. 1.1 mark: correct option (A) identified — X-rays, 1 nm to 10−310^{-3} nm.
  2. 2.No partial marks for MCQ; naming X-rays as the diagnostic wave is the key reasoning.

Hint

Which EM wave gives you a radiograph of a broken bone? Recall its wavelength band just below UV.

Quick oral answer

X-rays, with wavelengths from about 1 nanometre down to 10−310^{-3} nanometre, are used in medical diagnosis because their short wavelength lets them penetrate soft tissue while being absorbed by bone.

Common mistakes

  1. 1.Confusing X-rays with ultraviolet (400 nm to 1 nm) — UV is used for sterilisation, not imaging diagnosis.
  2. 2.Mixing up the order of the spectrum and assigning X-rays a longer wavelength than UV; X-rays are shorter (higher frequency) than UV.
  3. 3.Selecting microwaves/infrared because they are used in some medical therapies, forgetting the word 'diagnostic'.

Analysis and explanation

The question tests recall of the electromagnetic spectrum and the correct wavelength band of X-rays, the standard EM wave used for medical diagnosis.


Why (A) is correct:

  • X-rays span about 1 nm to 10−310^{-3} nm and are produced by decelerating high-energy electrons (Coulidge tube). Their short wavelength enables them to penetrate flesh and image bone, making them the diagnostic tool in radiography.

Why the others are wrong:

  • (B) 400 nm to 1 nm is the ultraviolet region — used in sterilisation, not routine diagnosis.
  • (C) 1 mm to 700 nm is the infrared region — used in thermal imaging and remote controls.
  • (D) 0.1 m to 1 mm is the microwave region — used in radar and communication.

Exam trap: Some students pick UV (B) because it is also "medical"; but UV is used for treatment/sterilisation, whereas imaging diagnosis uses X-rays.

Interesting facts

X-rays were discovered by Wilhelm Roentgen in 1895; he won the first Nobel Prize in Physics in 1901 and the first medical X-ray image was of his wife's hand.

A modern CT (computed tomography) scan combines hundreds of X-ray projections to build a 3-D image, a technique that earned Hounsfield and Cormack the 1979 Nobel Prize in Medicine.

Question details

Q7 of 39 questions

Board
CBSE
Class
Class 12
Subject
Physics
Year
2026
Section
Section A
Marks
1
Type
MCQ
Chapter
Electromagnetic Waves
Topic
Electromagnetic Spectrum — X-rays
Bloom's level
remember
Syllabus topic
Unit 6: Electromagnetic Waves — Electromagnetic Spectrum and Uses of X-rays
Author
CBSE
Reviewed by
Padhantu Academic Team

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Frequently asked questions

Why are X-rays used for medical diagnosis and not UV or microwaves?

X-rays have a very short wavelength (1 nm to 10−310^{-3} nm) and hence high penetrating power. They pass through soft tissue but are absorbed by dense bone, producing a contrast image. UV cannot penetrate the body and microwaves lack the resolution and are absorbed as heat.

How does the wavelength of X-rays compare with visible light?

Visible light spans roughly 400–700 nm, whereas X-rays are about a thousand to a million times shorter (1 nm to 10−310^{-3} nm), which is why X-rays carry far higher energy per photon.