Question

When a blackened bulb thermometer is moved beyond the red region of the visible spectrum, there is a rapid rise in the temperature. This is due to the presence of:

• A. Infrared radiations
• B. Ultraviolet radiations
• C. X-rays
• D. Radio waves

Hint:

Remember the order of the electromagnetic spectrum around visible light: Ultraviolet \(\rightarrow\) Visible (Violet to Red) \(\rightarrow\) Infrared. Infrared radiation is often called "heat radiation".

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The solar spectrum consists of visible light and invisible radiations. The region just beyond the red end of visible light is the infrared region.
Step 2: Detailed Explanation:
Infrared radiations are thermal radiations. They have high heating power because their frequencies match the vibrational frequencies of many molecules.
A blackened bulb absorbs these radiations efficiently, leading to a significant increase in temperature.
This property was used by William Herschel to discover infrared rays.
Step 3: Final Answer:
The heating effect beyond the red region is caused by infrared radiations.