Which of the following statements about X rays is not true according to basic physics and medical imaging?

Introduction / Context:

This conceptual physics question tests knowledge of the basic properties of X rays. X rays are a form of high energy electromagnetic radiation used widely in medical imaging, security scanners, and crystallography. Knowing which statements accurately describe X rays helps avoid misconceptions about their behaviour, risks, and applications.

Given Data / Assumptions:

• Four statements describe properties of X rays.
• We must identify the statement that is not true.
• Standard behaviour of X rays in vacuum and in matter is assumed.
• Basic facts from school level physics about electromagnetic waves are used.

Concept / Approach:

X rays are electromagnetic waves with short wavelength and high frequency. Like visible light, they travel at the speed of light in vacuum. They have strong penetrating power and can pass through many materials that visible light cannot, which is why they are used to see inside the human body or luggage. X rays can cause chemical changes and can expose photographic plates or films. Under special arrangements, such as crystals or multilayer mirrors, X rays can also show reflection, refraction and diffraction effects. Therefore, any statement claiming that X rays have low penetrating power is not correct.

Step-by-Step Solution:

Verification / Alternative check:

Medical X ray machines can produce images of bones and internal organs because X rays pass through soft tissues more easily than through bone, demonstrating significant penetration. Security scanners at airports also rely on the ability of X rays to pass through bags. If X rays truly had low penetrating power, they would be stopped at the surface and could not be used for these purposes. This practical evidence confirms that the statement claiming low penetrating power is incorrect.

Why Other Options Are Wrong:

• X rays travel with the speed of light in vacuum: This is correct for all electromagnetic waves, including X rays.
• X rays can be reflected, refracted or diffracted: Under special conditions, particularly with crystals and grazing incidence optics, X rays show these wave behaviours, so this is true.
• X rays can affect photographic plates: X rays cause chemical changes similar to visible light, so they can expose photographic film, which is a true statement.

Common Pitfalls:

Students sometimes think that because X rays are dangerous, they might be easily blocked, and therefore assume low penetration. In fact, the danger partly arises from their high penetration and ionising ability. Another confusion is to think only visible light gets reflected or refracted, forgetting that all electromagnetic waves can show these effects under suitable conditions. Keeping in mind that X rays are simply higher energy electromagnetic waves helps correct these misunderstandings.

Final Answer:

The statement that is not true is: X rays have low penetrating power in matter.