Problem 2 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is easily stopped by air? (a) uv rays (b) X-rays (c) \(\alpha\) rays (d) \(\gamma\) rays

Step-by-Step Solution

Answer

Alpha rays (b1 ext{ rays}) are easily stopped by air.

Step 1: Understanding the Radiation Types

We need to understand the types of radiation mentioned in the options and their ability to pass through materials like air. Alpha rays consist of helium nuclei and are known to be heavy and positively charged. They can be stopped by a sheet of paper or even air. UV rays are a form of electromagnetic radiation with shorter wavelengths than visible light. X-rays are another form of electromagnetic radiation but with much higher energy, and gamma rays are the most penetrating form of electromagnetic radiation, even more than X-rays.

Step 2: Analyzing Each Option

(a) UV rays - These can pass through air, but are partly absorbed by the ozone layer, which is a thick layer of air. (b) X-rays - These can pass through air and are not easily stopped by it. (c) Alpha rays - As previously noted, they are heavy particles that lose their energy quickly when passing through air. (d) Gamma rays - These are highly penetrative and can pass through air easily.

Step 3: Selecting the Correct Answer

From our analysis, we establish that alpha rays lose energy quickly and are easily stopped by air compared to the other types of radiation. Therefore, option (c) is the correct choice.

Key Concepts

Understanding Alpha Rays

Alpha rays are a type of ionizing radiation consisting of helium nuclei, which include two protons and two neutrons. This composition makes them relatively heavy compared to other forms of radiation like beta particles or electromagnetic waves.
Due to their mass and positive charge, alpha particles strongly interact with other matter, such as molecules in air, leading to rapid energy loss. This means they can only travel a few centimeters in the air before being absorbed or stopped.

• Heavy and positively charged (helium nuclei)
• Interact strongly with matter
• Short range and easily stopped by air

Despite their limited range and penetration power, alpha rays can be dangerous if alpha-emitting materials are ingested or inhaled, as they can cause significant damage to biological tissues at close range.

Electromagnetic Radiation Overview

Electromagnetic radiation encompasses a wide range of energy waves, from radio waves to gamma rays, all part of the electromagnetic spectrum. These waves differ in their frequency and wavelength, affecting their energy and penetration abilities.
UV rays, X-rays, and gamma rays are all forms of electromagnetic radiation but vary greatly in their properties:

• UV Rays: Slightly more energetic than visible light, they can damage surfaces but are less penetrating than X-rays.
• X-Rays: They have higher energy than UV rays, allowing them to penetrate through soft tissues, making them useful for medical imaging.
• Gamma Rays: As the most energetic form of electromagnetic radiation, they have extremely high penetration capabilities. They can pass through dense materials like concrete and even steel.

Electromagnetic radiation travels at the speed of light and does not consist of particles, allowing it to pass through air with relative ease.

Penetration Through Air: A Comparative Look

The ability of radiation to penetrate through air varies greatly between types, mainly based on its energy and composition.
Alpha particles are limited in this regard due to their mass, leading them to quickly lose energy and be stopped by air.

• Alpha Rays: Rapidly lose energy and are stopped within a few centimeters of air.
• UV Rays: Can pass through air but are partially absorbed by atmospheric elements like the ozone.
• X-Rays: More penetrating than UV rays, they can travel through air and even soft tissues.
• Gamma Rays: With the highest penetration power, they can pass through air, thick walls, and even lead.

Understanding these differences is crucial for safety and application, as choosing the right protective measures is essential based on the radiation type one might be exposed to.