Question

A fire screen produces sensation of cooling as
A. it allows both infrared and visible light but cuts off ultraviolet
B. It allows infrared and cuts off shorter wavelengths
C. It cuts off both visible light and infrared
D. It shows only visible light and cuts off infrared

Answer 1

Hint: Fire screens are used as a safeguard from the flying sparks which could give rise to potential fire accidents. The heat due to fire is thermal radiation made up of infrared, ultraviolet, and visible light. Most of the objects radiate heat in the form of infrared radiation. The reflection of infrared waves produces a cooling sensation.

Complete answer:
Fire screens are placed in front of the fireplace to protect the occupants of the room from open flames and the cinders released by the fire.
As they’re used as a shield to guard the sudden disruption of fire, the screen had to reduce the heat and keep from sparks flying into the room. Hence, they’re made of thermal insulators like glass.
Thermal radiation is the electromagnetic radiation emitted by heat.
The fire radiates most of the heat in the infrared spectrum, as it does not have enough energy to radiate at a higher frequency.
Being electromagnetic radiation, thermal radiation is made of electromagnetic waves ranging from ultraviolet light through visible light to infrared light.
While the ultraviolet waves and visible lights can pass through the glass surface, infrared waves cannot pass through the objects due to higher wavelengths. These infrared rays reflect into the fireplace. This is seen as a cooling sensation on the fire screen.
So, the fireplace screen only allows the passage of visible light and cuts off the infrared light.

Therefore, the correct option is D.

Note:
Don’t confuse, infrared radiation with thermal radiation. Infrared radiation is an integral part of thermal radiation.
You must understand that anything with a temperature greater than absolute zero gives off thermal radiation.
Many people assume that the infrared radiations are the cause of heat, but it isn’t the case. The actual case is that the object may have a lesser amount of energy. This lesser energy corresponds to lesser frequencies. The infrared waves are the electromagnetic waves with lesser frequencies than UV or visible light. Hence, the most of the part is infrared radiation.