Question

Order the following electromagnetic radiation in terms of their decreasing energy level
(A) Infrared rays
(B) Gamma rays
(C) Visible rays
(D) Radio waves
Choose the correct answer from the options given below :

• A. (A), (B), (C), (D).
• B. (B), (C), (A), (D).
• C. (B), (A), (D), (C).
• D. (C), (B), (D), (A).

Hint:

Remember the order of the electromagnetic spectrum from highest to lowest energy: Gamma $\rightarrow$ X-ray $\rightarrow$ UV $\rightarrow$ Visible $\rightarrow$ Infrared $\rightarrow$ Microwave $\rightarrow$ Radio.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Electromagnetic radiation propagates as waves with distinct wavelengths ($\lambda$) and frequencies ($\nu$).
The energy ($E$) of a single photon of electromagnetic radiation is directly proportional to its frequency and inversely proportional to its wavelength.

Step 2: Key Formula or Approach:
The relationship between photon energy and wavelength is given by Planck's equation:
\[ E = h\nu = \frac{hc}{\lambda} \]
where $h$ is Planck's constant and $c$ is the speed of light.
According to this relationship, shorter wavelengths correspond to higher energy levels.

Step 3: Detailed Explanation:
Let us compare the wavelengths and energy levels of the given electromagnetic regions:
1. Gamma rays (B): These have the shortest wavelengths ($< 10^{-11} \text{ m}$) and the highest frequencies in the electromagnetic spectrum, making them the most energetic radiation.
2. Visible rays (C): These lie in a narrow band with wavelengths ranging from approximately $380 \text{ nm}$ (violet) to $750 \text{ nm}$ (red). Their energy is significantly lower than gamma rays but higher than infrared.
3. Infrared rays (A): These have longer wavelengths ($750 \text{ nm}$ to $1 \text{ mm}$) than visible light, corresponding to lower frequency and lower photon energy.
4. Radio waves (D): These have the longest wavelengths ($1 \text{ mm}$ to $> 100 \text{ km}$) and the lowest frequencies, making them the least energetic radiation in the spectrum.
Arranging these in order of decreasing energy level yields:
Gamma rays (B) $\rightarrow$ Visible rays (C) $\rightarrow$ Infrared rays (A) $\rightarrow$ Radio waves (D).
This corresponds to the sequence: (B), (C), (A), (D).

Step 4: Final Answer:
The correct decreasing energy sequence is (B), (C), (A), (D), corresponding to option (B).